Soil science in fifteen seconds

Short animated explainers on how living soil and medical cannabis cropping actually work. Grouped by topic; tap any tile to watch.

    Soil growing

    Growing in the ground: structure, temperature, cover crops and water.

    • Soil structure

      Structure is the delivery system. Biology builds the crumb.

      Sources: Weil & Brady 2017, The Nature and Properties of Soils, 15th edn, ch. 4; Six et al. 2004, Soil and Tillage Research; Dontsova & Norton 2002, Soil Science Full references

    • Soil temperature is the clock

      Soil life works to soil temperature, not the calendar. Compost slows most in cold soil.

      Sources: Sullivan et al. 2019, OSU Extension EM 9235; Hartz & Johnstone 2006, HortTechnology; Agehara & Warncke 2005, Soil Sci. Soc. Am. J. Full references

    • Cover crops are a nitrogen bank

      Legumes pull nitrogen from the air and bank it in the soil. Half is yours this season.

      Sources: Ferretti 2023, A practical guide for using green crops in New Zealand (Our Land and Water); Clark (ed.) 2007, Managing Cover Crops Profitably, 3rd edn (SARE) Full references

    • Water deep, water seldom

      In soil: soak the root zone, then let the top dry. Each dry-down pulls air in.

      Sources: Weil & Brady 2017, The Nature and Properties of Soils, 15th edn, ch. 5, 6 and 7 Full references

    • Roots feel tension, not litres

      A tensiometer reads how hard roots must pull for water. Litres and percent mean different things in each soil.

      Sources: Lena et al. 2021, Alabama Extension ANR-2774, Irrigation Scheduling Using Soil Water Tension Sensors; Klopp and Bly 2024, SDSU Extension, How Soil Holds Water; Lieth and Oki 2008, Irrigation in soilless production (in Soilless Culture, Elsevier); Montesano et al. 2015, Frontiers in Plant Science Full references

    • Dry topsoil seals the tank

      Outdoors, once the bare surface of garden soil dries, water below can only leave as vapour, and evaporation slows.

      Sources: Allen, Pereira, Raes and Smith 1998, Crop evapotranspiration, FAO Irrigation and Drainage Paper 56, chs 7 and 10; Shokri and Or 2011, What determines drying rates at the onset of diffusion controlled stage-2 evaporation from porous media? (Water Resources Research); Or, Lehmann, Shahraeeni and Shokri 2013, Advances in soil evaporation physics: a review (Vadose Zone Journal) Full references

    Soil testing

    How to take a sample, which test to ask for, and how to read what comes back.

    • Sample your soil like the lab expects

      Fifteen to 20 cores, 150 mm deep, in a zigzag across the block. One bucket, one bag, one number you can trust.

      Sources: Hill Laboratories 2023, Self-Sampling Guide; Morton, Roberts & Power (eds) 2024, Sampling Pastoral, Arable and Horticultural Soils, Fertiliser Association of NZ Full references

    • Read your water test before the soil test

      1 mg/L in the water is 1 kg/ha for every 100 mm you apply. Put it in the budget.

      Sources: Ayers and Westcot 1985, FAO Irrigation and Drainage Paper 29; Flynn 2009, NMSU Guide W-102 Full references

    • Savings account, wallet

      A standard soil test counts what the soil holds. A water extract counts what is dissolved today.

      Sources: Hill Laboratories Technical Notes KB3196 (Soil Tests and Interpretation), KB3188 (Cation Exchange Capacity and Base Saturation) and KB3184 (Potting Media); Saha 2022, UGA Extension Circular 1040; Logan Labs, Our Services Full references

    • CEC: how big is your pantry

      Clay and humus hold calcium, magnesium and potassium against leaching. Sand holds very little.

      Sources: Hill Laboratories Technical Notes KB3188 (Cation Exchange Capacity and Base Saturation) and KB3196 (Soil Tests and Interpretation); Saha 2022, UGA Extension Circular 1040; Mengel, Purdue Extension AY-238 Full references

    • Hydrogen holds the seats

      Every exchange site is always taken. In an acid soil hydrogen and aluminium sit where calcium could.

      Sources: Hill Laboratories Technical Notes KB3188 (Cation Exchange Capacity and Base Saturation) and KB3196 (Soil Tests and Interpretation); Mengel, Purdue Extension AY-238 Full references

    • pH is not a calcium test

      Magnesium, potassium and sodium are bases too. They hold pH up, so a good pH can hide low calcium.

      Sources: Hill Laboratories, Technical Note KB 3188, Cation Exchange Capacity and Base Saturation; Hill Laboratories, Technical Note KB 3196, Soil Tests and Interpretation; Horneck et al. 2011, Soil Test Interpretation Guide, Oregon State University Extension EC 1478 Full references

    • Same soil, two phosphorus numbers

      New Zealand labs report Olsen P. Many overseas guides quote Mehlich 3 or Bray. The numbers do not swap.

      Sources: Hill Laboratories, Technical Note KB 26049, Soil Phosphorus Tests; Hill Laboratories, Technical Note KB 3196, Soil Tests and Interpretation; Sawyer and Mallarino 1999, Differentiating and Understanding the Mehlich 3, Bray, and Olsen Soil Phosphorus Tests, Iowa State University; Ketterings and Barney 2010, Phosphorus Soil Testing Methods, Cornell University Agronomy Fact Sheet 15 Full references

    • Beds are volume, not area

      A kilograms per hectare rate from a soil report is spread through the sampled depth: 150 mm for crops.

      Sources: Hill Laboratories, Analysis Request form sampling instructions and Technical Note KB 3196 (Soil Tests and Interpretation); Fertiliser Association of New Zealand 2024, Sampling Pastoral, Arable and Horticultural Soils Full references

    Indoor living soil growing

    Pots and beds of living soil under lights: moisture, roots, canopy work and keeping the plant moving.

    • Living soil media: keep it evenly moist

      Microbes live in the water film on every particle. Living Soil v2 target: 70 to 120 mbar on a Blumat meter.

      Sources: Raviv, Lieth and Bar-Tal (eds) 2019, Soilless Culture; Lieth and Oki 2008, Irrigation in soilless production; Montesano et al. 2015, Frontiers in Plant Science; Michel 2009, HortScience; Seacliff Organics, Living Soil v2 product page Full references

    • Dry pockets: roots you never fed

      Water channels down the sides and leaves a dry core. Water in rounds, not one pour.

      Sources: Fields, Fonteno & Jackson 2014, HortScience 49(3); Raviv, Lieth & Bar-Tal (eds) 2019, Soilless Culture: Theory and Practice, 2nd edn, ch. 3 and 9 Full references

    • Never let it stall

      In our experience one big stress event can cost a week. A crop that never stalls usually beats a rescue.

      Sources: Chandra et al. 2008, Physiol. Mol. Biol. Plants 14(4) (heat and photosynthesis only) Full references

    • Mycorrhizae go on the roots

      Spores do not move. Dust the rootball at every up-pot; watered through the soil, most of it is wasted.

      Sources: Smith & Read 2008, Mycorrhizal Symbiosis, 3rd edn, ch. 2 and 17; Besserer et al. 2006, PLoS Biology 4(7) Full references

    • Defoliation: when, how much, why

      Twice: at the flip and three weeks in, never more than a fifth. Nothing after week four.

      Sources: Danziger & Bernstein 2021, Industrial Crops and Products 167; Danziger & Bernstein 2021, Plants 10(9) Full references

    Environmental control

    Air, VPD, temperature, light and the instruments you run the room with.

    • Keep the air moving in one direction

      At least 1 m/s over the canopy, in a loop that passes every plant and the dehumidifier.

      Sources: Anderson 2026, Pipp Horticulture (Cannabis Research Coalition airflow trials); Justice 2026, CannMed abstract; Kitaya et al. 2003, Advances in Space Research; Dupont et al. 2025, Journal of Experimental Botany; Peiro et al. 2020, Frontiers in Plant Science Full references

    • Oscillating fans wreck your airflow

      They blast, then stall. Every leaf gets a different climate every ten seconds.

      Sources: Kitaya et al. 2003, Advances in Space Research; Dupont et al. 2025, Journal of Experimental Botany. The fixed-fan advice is grower practice. Full references

    • Canopy wind speed: two sets of numbers

      Medical cannabis trials point to 1 to 2 m/s at the canopy. Tomato and sweetpotato work levels off by 0.5 to 1.

      Sources: Anderson 2026, Pipp Horticulture (Cannabis Research Coalition airflow trials); Justice 2026, CannMed abstract; Kitaya et al. 2003 and 2004, Advances in Space Research; Dupont et al. 2025, Journal of Experimental Botany; Shapira et al. 2024, The Plant Journal Full references

    • VPD and temperature by stage

      Clone 0.6, veg 1.0, early flower 1.2, late flower 1.4 kPa. Cooler and drier as the buds fill.

      Sources: Allen et al. 1998, FAO Irrigation and Drainage Paper 56 (the VPD calculation); Nelson & Bugbee 2015, PLoS ONE (leaf temperature); Grossiord et al. 2020, New Phytologist. Stage targets are common grower practice. Full references

    • VPD swings lower your yield

      Stomata are slow to follow a changing room. While they lag, the leaf takes in less CO2.

      Sources: Grossiord et al. 2020, New Phytologist; Lawson & Blatt 2014, Plant Physiology; McAusland et al. 2016, New Phytologist Full references

    • Measure VPD at the leaf

      Air temperature, humidity, and the leaf itself with an infrared thermometer. Leaf VPD, not air VPD.

      Sources: Allen et al. 1998, FAO Irrigation and Drainage Paper 56, ch. 3; Resource Innovation Institute 2022, HVAC Best Practices Guide for CEA; Nelson & Bugbee 2015, PLoS ONE; Grossiord et al. 2020, New Phytologist Full references

    • Calibrate your humidity meter

      Saturated salt reads 75%. Whatever yours says, the difference is your offset. Repeat every three months.

      Sources: Greenspan 1977, Journal of Research of the National Bureau of Standards 81A(1) Full references

    • Temperature sets the speed limit

      PPFD, CO₂, temperature, feed EC and VPD work together. Light pays alone, and better with the rest.

      Sources: Rodriguez-Morrison, Llewellyn & Zheng 2021, Frontiers in Plant Science; Chandra et al. 2008, Physiol. Mol. Biol. Plants; Llewellyn et al. 2022, Frontiers in Plant Science Full references

    • Where the dehumidifier goes

      In the airstream, at canopy height, downstream of the plants. Not in a corner.

      Sources: Resource Innovation Institute 2022, HVAC Best Practices Guide for CEA; ASHRAE 2021, Handbook: Fundamentals, ch. 1 Full references

    • Buds make their own weather

      Inside a dense flower the air is more humid than the room sensor reads. Mould starts there.

      Sources: Buirs, Lung and Punja 2025, Canadian Journal of Plant Pathology 47(5):443; Thomas, Marois and English 1988, Phytopathology 78:260; English et al. 1989, Phytopathology 79:395 Full references

    • Drying medical cannabis: set points

      Hold the dew point, not just the room: about 18 to 20 C with a dew point near 12 C, then finish by water activity.

      Sources: Justice 2025, Cannabis Research Coalition (Cannatrol Cool Cure trial); Sandelman 2025, HPAC Engineering; Cannatrol, Cool Cure setup guide; ASTM D8197-22 and D8196-22; Das et al. 2022, Bioengineering Full references

    Microbes

    The biology that does the feeding, and how to keep it alive.

    • Soil biology

      The root runs a factory: the plant pays in carbon, microbes deliver the rest.

      Sources: Bardgett & van der Putten 2014, Nature; Lynch & Whipps 1990, Plant and Soil; Bonkowski 2004, New Phytologist; Jakobsen, Abbott & Robson 1992, New Phytologist Full references

    • How we make our inoculant

      Grown on our land. One lineage, eight years and 50-plus microscope assays deep.

      Sources: Johnson and DeSimio 2017, Best Management Practices: Johnson-Su Composting Bioreactors, NMSU (the bioreactor method). The lineage, the forest floor start, Lex's pile, the passage from batch to batch and the 50-plus Soil Food Web assays are Seacliff's own record. Full references

    • The root's bodyguards

      Bacillus subtilis films the root, Trichoderma eats what gets through. Occupy the root first.

      Sources: Harman et al. 2004, Nature Reviews Microbiology; Hashem et al. 2019, Saudi Journal of Biological Sciences; Chitarra et al. 2003, Journal of Applied Microbiology Full references

    • Chlorine stops at the surface

      Town water chlorine is spent in the top 13 mm. Living soil does not need a filter.

      Sources: Colorado State University Extension, PlantTalk 1548; Water Services Authority - Taumata Arowai 2025, Chlorine Full references

    • The poop loop

      Protozoa and nematodes eat bacteria, keep the carbon and poop out the spare nitrogen as ammonium at the root.

      Sources: Ingham 2000, Soil Biology Primer (NRCS); Ingham, Trofymow, Ingham and Coleman 1985, Ecological Monographs; Bonkowski 2004, New Phytologist; Soil Food Web School, Nutrient Cycling; Werblow 2023, The Furrow Full references

    • Rhizophagy: roots eat microbes

      Microbes enter root tip cells, the root strips their nutrients with reactive oxygen, and survivors leave by the root hairs.

      Sources: White, Kingsley, Verma and Kowalski 2018, Microorganisms; Paungfoo-Lonhienne et al. 2010, PLoS ONE Full references

    • Mycorrhizal fungi: ecto and endo

      Fungal threads trade phosphorus, nitrogen and water for the plant's sugar. Two ways in: inside the cells, or around them.

      Sources: Ingham 2000, Soil Biology Primer (NRCS); Brundrett and Tedersoo 2018, New Phytologist; van der Heijden et al. 2015, New Phytologist; Smith et al. 2011, Plant Physiology; Citterio et al. 2005, Chemosphere Full references

    • The organic nitrogen cycle

      Nitrogen enters as gas, lives as protein, and leaves as gas or nitrate. Everything in between is done by microbes.

      Sources: Robertson and Groffman 2015, Nitrogen transformations, in Soil Microbiology, Ecology and Biochemistry, 4th edn; Stein and Klotz 2016, Current Biology Full references

    • Rhizobia: pink means working

      The bacteria only fix nitrogen inside the root nodule, and only while the nodule is red. The red is leghaemoglobin, holding oxygen away from the enzyme.

      Sources: Ott et al. 2005, Current Biology (no leghaemoglobin, no fixation); Meat and Livestock Australia, How to assess legume nodulation (dig at 12 weeks, 20 nodules, pink is effective, white is not) Full references

    • Free-living nitrogen fixers

      No nodule, no host. Bacteria on and near the root fix nitrogen from the air in exchange for the sugar the root leaks.

      Sources: Reed, Cleveland and Townsend 2011, Annual Review of Ecology, Evolution, and Systematics; Smercina et al. 2019, Applied and Environmental Microbiology; Ladha et al. 2016, Scientific Reports Full references

    Composting

    Hot piles, worm farms and the no-turn bioreactor: how each one works, the numbers that matter, and what to do with the compost.

    • Just add compost

      Three bags, one name. Potassium ten times apart, magnesium four times, pH 5.6 to 8.6. Compost is not a number.

      Sources: Jasim and Smith 2003, The practicability of home composting (Imperial College London), Section 6; Sullivan and Miller 2001, Compost quality attributes, measurements and variability (CRC Press); Hill Laboratories, Guidelines for Interpreting Your Compost Analysis Report (KB 7809) Full references

    • Compost for nitrogen overshoots phosphorus

      Compost releases about a tenth of its nitrogen in year one. Dose it for nitrogen and phosphorus piles up.

      Sources: Sullivan et al. 2018, Interpreting Compost Analyses (OSU Extension EM 9217); Sullivan et al. 2019, OSU Organic Fertilizer and Cover Crop Calculator (EM 9235); DuPont and Granatstein 2020, Compost Considerations (WSU Extension); Reid and Morton 2019, Nutrient Management for Vegetable Crops in New Zealand Full references

    • Manure overshoots phosphorus too

      Dose any manure for nitrogen and it brings many times the phosphorus the crop takes up.

      Sources: AHDB 2023, Nutrient Management Guide (RB209) Section 2: Organic materials; Bary, Cogger and Sullivan 2016, Fertilizing with Manure and Other Organic Amendments (PNW 533); Griffiths 1998, Best practice guidelines for using poultry litter on pastures (NSW Agriculture); Mahr, Using Manure in the Home Garden (University of Wisconsin-Madison Extension); Reid and Morton 2019, Nutrient Management for Vegetable Crops in New Zealand Full references

    • Thermophilic compost: temps and turns

      Hot, wet, turned five times, then patient. The heat is two weeks; the compost is a year.

      Sources: Seacliff Organics, Thermophilic Composting (blog); Rittenhouse 2015, NCAT ATTRA Tipsheet: Compost (USDA organic rule 7 CFR 205.203) Full references

    • A worm farm that is not too wet

      Leachate is not worm tea. A dry-ish bin makes castings; a wet one makes smell.

      Sources: Sherman 2017, NC State Extension AG-473-18; University of Arizona Cooperative Extension 2021, Wind and Weeds Full references

    • Johnson-Su: the no-turn compost

      Never turned, never smells, fungal when it is done. Air within 30 cm of everything is the trick.

      Sources: Johnson and DeSimio 2017, Best Management Practices: Johnson-Su Composting Bioreactors, NMSU; Seacliff Organics, DIY Johnson Su Bioreactor (blog) Full references

    Biostimulants

    Hormones, foliars, surfactants and what is actually in the bag.

    • What's in the bag

      Living Soil v2: a base that holds water and air, minerals for the whole cycle, biology to run it.

      Sources: Seacliff Organics, Living Soil v2 product page; Hill Laboratories 2022, Certificate of Analysis 2965941 (Seacliff Lab tests page); Hill Laboratories, Guidelines for Interpreting Your Compost Analysis Report (KB 7809) Full references

    • Foliars: fast fixes, then the soil

      A fine mist on both leaf sides reaches the plant in hours. Lights off, both sides, surfactant.

      Sources: Fernández, Sotiropoulos & Brown 2013, Foliar Fertilization: Scientific Principles and Field Practices, IFA Full references

    • Yucca and quillaja: make water wet

      Saponins drop surface tension so sprays spread on the leaf and water sinks into dry media.

      Sources: Ulaganathan et al. 2019, Colloids and Surfaces B (quillaja saponin and surface tension); Güçlü-Üstündağ & Mazza 2007, Crit. Rev. Food Sci. Nutr.; Fields, Fonteno & Jackson 2014, HortScience (wetting agents in peat and coir); Fernández, Sotiropoulos & Brown 2013, IFA Full references

    • Kelp is not fertiliser

      Kelp meal is about one percent nitrogen. A garden dressing brings under a tenth of the nitrogen a crop takes up.

      Sources: OMRI Products List, Acadian Seaplants Kelp Meal 1.0-0.15-2.0; Almeida et al. 2024, JDS Communications (lab analysis of Acadian kelp meal); Reid and Morton 2019, Nutrient management for vegetable crops in New Zealand; Shukla et al. 2019, Frontiers in Plant Science (review of Ascophyllum nodosum biostimulants) Full references

    • Humates: modest, not magic

      Across trials humic substances lift growth by about a fifth on average, with wide swings between trials.

      Sources: Rose et al. 2014, Advances in Agronomy (meta-analysis of plant growth response to humic substances), figures as quoted by Nardi et al. 2021, Molecules; Lyons and Genc 2016, Agronomy (commercial humates in the field); Olk et al. 2018, Journal of Soils and Sediments (review of humic products); Li, Van Gerrewey and Geelen 2022, Frontiers in Plant Science (meta-analysis of biostimulant field trials) Full references

    • Amino acids: fast nitrogen

      An amino acid is nitrogen the plant can take as it is. In soil it is also the fastest meal there is: half gone in hours.

      Sources: Jones 1999, Soil Biology and Biochemistry; Jones and Kielland 2002, Soil Biology and Biochemistry; Näsholm, Kielland and Ganeteg 2009, New Phytologist; Ingham 2000, Soil Biology Primer; Seacliff Organics, Amino Acid Powder product page Full references

    • Fulvic acid: the small chelator

      The smallest, most soluble humic fraction. It grips iron, zinc and other metals and keeps them in solution for the root.

      Sources: Zanin, Tomasi, Cesco, Varanini and Pinton 2019, Frontiers in Plant Science; Seacliff Organics, Liquid Fulvic and NTS Fulvic Acid product pages Full references

    • Aloe for cuttings

      Whole leaf aloe as a soak and a dip. In the trial that measured it, cuttings in soil grew longer roots.

      Sources: Yüksek et al. 2026, Plants; Seacliff Organics, Whole Leaf Aloe Powder and Aloe Pro product pages Full references

    • Kelp for cuttings

      A soluble kelp dip at the base before the medium. In the trials that measured it, more cuttings rooted and roots grew longer.

      Sources: Gomes et al. 2018, Ornamental Horticulture (Ascophyllum extract on passionflower cuttings); Luna Rodríguez et al. 2024, Agronomía Costarricense (Ascophyllum extract on spearmint cuttings); Stirk and Van Staden 1996, Journal of Applied Phycology; Seacliff Organics, Tri-Kelp product page Full references

    • Auxins: the tip rules

      Made in the shoot tip and young leaves, pushed down the stem cell by cell. Where it is high the tip grows; below it the side buds wait.

      Sources: Thimann and Skoog 1933, PNAS (apical dominance); Caplan et al. 2018, Canadian Journal of Plant Science (cannabis cuttings, IBA versus willow); Stirk and Van Staden 1996, Journal of Applied Phycology (auxin-like activity in seaweed extracts); Taiz et al. 2015, Plant Physiology and Development Full references

    • Gibberellins: stretch and wake

      The stem stretch signal and the seed wake-up call. Dwarf wheat is dwarf because it stopped listening to it.

      Sources: Peng et al. 1999, Nature (Green Revolution Rht genes); Paleg 1960, Plant Physiology (gibberellic acid and barley amylase); Mohan Ram and Jaiswal 1972, Planta (gibberellins induce male flowers on female cannabis); Taiz et al. 2015 Full references

    • Cytokinins: the root's reply

      Made in the root tips, carried up in the water stream. Cell division, side shoots, and leaves that stay green longer.

      Sources: Richmond and Lang 1957, Science (kinetin delays leaf senescence); Letham 1963, Life Sciences (zeatin from maize); Yong et al. 2009, Molecules (cytokinins in coconut water); Stirk and Van Staden 1996, Journal of Applied Phycology; Taiz et al. 2015 Full references

    • The rest of the signal kit

      Seven more signals the plant runs on. Each one is a switch, not a food.

      Sources: Yang and Hoffman 1984, Annual Review of Plant Physiology; Mittelheuser and Van Steveninck 1969, Nature; Grove et al. 1979, Nature; Malamy et al. 1990, Science; Farmer and Ryan 1990, PNAS; Gomez-Roldan et al. 2008, Nature; Ries et al. 1977, Science Full references

    Agronomy

    Testing, nutrient timing, ratios, inputs, and the marketing to see through.

    • Calcium, magnesium, and the one-off till

      Calcium helps clay hold an open crumb. Well out of range? Fix it with gypsum, ag lime or oyster grit, till once, then stop. The workable range is wide.

      Sources: Kopittke & Menzies 2007, Soil Sci. Soc. Am. J.; Chaganti et al. 2021, Agronomy Journal; Chaganti & Culman 2017, Crop, Forage & Turfgrass Management; Dontsova & Norton 2002, Soil Science; Hill Laboratories, Technical Note KB 3188; Lefever et al. 2014, Cornell Agronomy Fact Sheet 83; Lee et al. 2008, Waste Management; Roberts & Morton (eds) 2023, Fertiliser Association of NZ Full references

    • Gypsum: calcium without the pH

      Lime and gypsum both add calcium. Only lime moves pH: carbonate neutralises acid, sulphate does not.

      Sources: Lefever et al. 2014, Gypsum for Field Crops in New York (Cornell Agronomy Fact Sheet 83); Beegle and Lingenfelter 2014, Soil Acidity and Aglime (Penn State Extension); Lee et al. 2008, Oyster shell as a liming material (Waste Management 28:2702) Full references

    • Too much of a good thing

      Every mineral has a partner. Excess pushes others off the exchange sites.

      Sources: Xie et al. 2021, The Crop Journal; Ova et al. 2015, Plant and Soil; Rietra et al. 2017, Commun. Soil Sci. Plant Anal.; Kopittke & Menzies 2007, Soil Sci. Soc. Am. J. (the critical review of ratio balancing); Albrecht 1975, The Albrecht Papers (origin of the idea) Full references

    • Particle size sets the clock

      Same mineral, same dose: fine feeds now, coarse feeds later.

      Sources: Scott et al. 1992, Australian Journal of Agricultural Research; Kanabo & Gilkes 1988, Fertilizer Research; Watkinson 1994, Australian Journal of Soil Research Full references

    • Nitrogen for the whole crop

      Fast spikes versus slow humps, stacked to match demand.

      Sources: Sullivan et al. 2019, OSU Extension EM 9235; Hartz & Johnstone 2006, HortTechnology; Lazicki et al. 2020, J. Environ. Qual.; Di & Cameron 2002, Nutr. Cycl. Agroecosyst. Full references

    • Carbon decides when N shows up

      Every organic input has a C:N ratio. It sets release, or theft.

      Sources: Lazicki et al. 2020, J. Environ. Qual.; Sullivan et al. 2019, OSU Extension EM 9235; Clark (ed.) 2007, Managing Cover Crops Profitably (SARE); Ferretti 2023, Our Land and Water Full references

    • Nitrate leaches, ammonium waits

      Soil barely holds nitrate. A wet spell can wash much of a feed below the roots.

      Sources: Di & Cameron 2002, Nutr. Cycl. Agroecosyst.; Weil & Brady 2017, The Nature and Properties of Soils, 15th edn, ch. 8 Full references

    • Too much P turns mycorrhizae down

      The fungus trades phosphorus for sugar. When P is plentiful, the plant winds the trade back.

      Sources: Breuillin et al. 2010, The Plant Journal; Deng et al. 2014, PLoS ONE; Gosling et al. 2013, New Phytologist; Ova et al. 2015, Plant and Soil Full references

    • Phosphate stays where it lands

      Phosphate binds to soil within millimetres of where it lands. Nitrate goes wherever the water goes.

      Sources: Grant and Flaten 2019, 4R Management of Phosphorus Fertilizer in the Northern Great Plains, ch. 3; Beegle and Durst 2017, Managing Phosphorus for Crop Production (Penn State Extension); Clark and Beegle 2025, Nutrient Management to Improve Nitrogen Efficiency and Reduce Environmental Loss (Penn State Extension) Full references

    • Soil pH, water pH: how to move it

      Living soil runs 6.2 to 7.2, target 6.6. Water in at 6.0 to 6.5. Down with phosphoric acid, up with potassium silicate.

      Sources: Weil & Brady 2017, The Nature and Properties of Soils, 15th edn, ch. 9; McCauley, Jones & Olson-Rutz 2017, Montana State University Extension, Soil pH and Organic Matter Full references

    • Wood ash is lime in disguise

      Wood ash is a fast liming material with a little potassium in it. Rate it by what it does to pH.

      Sources: Griffin 2004, Using Wood Ash on Your Farm (University of Maine Extension Bulletin 2279); Saunders 2018, Guide to Using Wood Ash as an Agricultural Soil Amendment (UNH Extension); Browning 2019, Using Wood Ash in the Garden (Nebraska Extension); Environment Canterbury, Rural waste prevention and management; Safa et al. 2020, Environmental Pollution 262:114218 Full references

    • Hard water limes every watering

      Bicarbonate in bore or hard tap water is a little lime in every can. Alkalinity moves the pot, not water pH.

      Sources: Lopez, Mickelbart and Pasian 2010, Alkalinity Management in Soilless Substrates (Purdue Extension HO-242-W); Cox 1995, Water Quality: pH and Alkalinity (UMass Extension); Argo and Biernbaum 1996, J. Amer. Soc. Hort. Sci. 121:442 Full references

    • Everything in, nothing screened

      An untested input can carry heavy metals, herbicide, salt and a mineral excess you cannot see.

      Sources: EPA 2023, Advisory about clopyralid; Stanway 2024, Keeping clopyralid out of composts (WasteMINZ); Hill Laboratories KB 7809; Sullivan and Miller 2001; Seacliff Organics, Soil and Modified Medium Testing Services Full references

    • More isn't better

      Throw every bag in at any rate and you add salt, sodium, excess minerals and passengers you never measured.

      Sources: Hill Laboratories, Potting Media (KB 3184); Ova et al. 2015, Plant and Soil; Nelson and Janke 2007, HortTechnology; EPA 2023, Advisory about clopyralid; Hill Laboratories KB 7809; Sullivan and Miller 2001 Full references

    • Rock dust: use it on purpose

      Pick the rock for what it carries, dose it by the maths, then measure what changed.

      Sources: Lewis et al. 2021, Applied Geochemistry (basalt dust analyses); Beerling et al. 2024, PNAS (four year basalt field trial); Swoboda, Doring and Hamer 2022, Science of the Total Environment (review of 48 crop trials); Ramezanian et al. 2013, Plant and Soil (three year rock dust trial); International Zinc Association, Zinc in Fertilizer fact sheet Full references

    • What's blocking your minerals

      Stuff your intuition cannot see, and putting more on won't fix.

      Sources: Xie et al. 2021, The Crop Journal; Ova et al. 2015, Plant and Soil; Rietra et al. 2017, Commun. Soil Sci. Plant Anal.; Kopittke & Menzies 2007, Soil Sci. Soc. Am. J. (the critical review) Full references

    • Every amendment brings passengers

      No input supplies just one thing. Each bag carries a second nutrient along with the one you bought it for.

      Sources: Ballance Agri-Nutrients 2026, product analyses for Pure Gypsum, Pure Dolomite and Pure Sulphate of Potash; Seacliff Organics 2026, Acadian Kelp Meal typical analysis Full references

    • Mulder's chart: what blocks what

      The 1950s wheel of nutrient interactions, drawn in full. Solid arrows block, dashed arrows raise the need. A modern review found most interactions help, not hurt.

      Sources: NutriAg Academy 2020, Mulder's Chart: Nutrient Interactions; Canna, Interactions between nutrients; Rietra, Heinen, Dimkpa and Bindraban 2017, Communications in Soil Science and Plant Analysis; Xie et al. 2021, The Crop Journal; Ova et al. 2015, Plant and Soil Full references

    • Microbes unlock the phosphate

      Organic phosphorus moves at the speed of the microbes. Keep them fed and moist.

      Sources: Richardson and Simpson 2011, Plant Physiology; Alori, Glick and Babalola 2017, Frontiers in Microbiology Full references

    • Foliar sprays: read the tissue test

      One element, from the test, as a top up. Fix the excess in the soil so the block goes away.

      Sources: Jones and Jacobsen 2009, MSU Extension Nutrient Management Module 7; Fernandez, Sotiropoulos and Brown 2013, IFA Foliar Fertilization; Rietra et al. 2017, Communications in Soil Science and Plant Analysis; Xie et al. 2021, The Crop Journal Full references

    • pH sets what the roots can take

      The classic chart: one band per nutrient, wider where more of it sits in a form roots can use. Mineral soil, pH 4 to 9.

      Sources: Truog 1947, Soil Science Society of America Journal (the diagram); Hartemink and Barrow 2023, Plant and Soil (the diagram is conceptual); Barrow and Hartemink 2023, Plant and Soil (roots change uptake with pH); Criscione 2025, Virginia Cooperative Extension SPES-718 (soilless media 5.0 to 6.5) Full references

    • Eh: the other dial next to pH

      Redox potential in millivolts. pH says how many protons; Eh says how hard the soil pushes electrons. Together they set the form every element takes.

      Sources: Pezeshki and DeLaune 2012, Biology (Eh thresholds for oxygen, nitrate, iron and manganese; flooded soils); Husson et al. 2021, Plant and Soil (Eh near roots and earthworm channels; nitrate versus ammonium); Husson 2013, Plant and Soil (Eh and pH as joint drivers) Full references

    • Crops take different nitrogen, and when

      A pea wants a tenth of what celery wants, and a lettuce wants it early while a tomato wants it mid-season.

      Sources: Seacliff Organics, Market garden soil planner (per-crop targets and uptake shapes); Reid and Morton 2019, Nutrient management for vegetable crops in New Zealand; Cassity-Duffey et al. 2020, Soil Science Society of America Journal Full references

    Minerals and what they do

    One clip per mineral: its job, what deficiency looks like, what to feed it with, and what to watch.

    • Old leaves or new leaves?

      Where a deficiency shows first tells you which nutrients to suspect.

      Sources: McCauley, Jones and Jacobsen 2011, MSU Extension Nutrient Management Module 9; Cockson et al. 2019, Applied Sciences 9(20):4432; Maillard et al. 2015, Frontiers in Plant Science 6:317 Full references

    • Nitrogen: what it does

      Builds protein and chlorophyll. Mobile: old leaves tell you first.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms Full references

    • Phosphorus: what it does

      Energy, roots and flowering. Purple old leaves, cold roots.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Ova et al. 2015, Plant and Soil Full references

    • Purple is not always phosphorus

      Genetics, cold roots, strong light or a real shortage can all turn a plant purple.

      Sources: Nielsen 2022, Prevalent Purple Plants Perennially Puzzle Producers, Purdue University; McCauley, Jones and Jacobsen 2011, MSU Extension Nutrient Management Module 9; Mackay and Barber 1984, Soil Sci. Soc. Am. J. 48:818; Chalker-Scott 1999, Photochem. Photobiol. 70:1 Full references

    • Potassium: what it does

      Water regulation and bud density. Burnt edges on old leaves.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms Full references

    • Calcium: what it does

      Cell walls and root tips. Immobile: twisted new growth shows it first.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; White & Broadley 2003, Annals of Botany; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Dontsova & Norton 2002, Soil Science; Lefever et al. 2014, Cornell Agronomy Fact Sheet 83 Full references

    • Magnesium: what it does

      The atom at the centre of chlorophyll. Green veins, yellow between, on old leaves.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Dontsova & Norton 2002, Soil Science Full references

    • Sulphur: what it does

      Proteins, oils and flavour compounds. Pale young leaves.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 6; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; McCauley, Jones & Olson-Rutz 2017, Montana State University Extension, Soil pH and Organic Matter Full references

    • Iron: what it does

      Chlorophyll and photosynthesis. Yellow new leaves with green veins; usually a pH problem.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Jones & Jacobsen 2009, Montana State University Extension, Micronutrients Full references

    • Manganese: what it does

      Splits water in photosynthesis. Speckled young leaves.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; McCauley, Jones & Olson-Rutz 2017, Montana State University Extension, Soil pH and Organic Matter Full references

    • Zinc: what it does

      Makes auxin. Small leaves and bunched tips; high phosphorus is the usual cause.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Jones & Jacobsen 2009, Montana State University Extension, Micronutrients Full references

    • Copper: what it does

      Lignin, pollen and disease resistance. Dying tips; a narrow, toxic range.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Roberts & Morton (eds) 2023, Fertiliser Use on New Zealand Dairy Farms Full references

    • Boron: what it does

      Cell walls, pollen and seed set. Dead growing points; never guess the dose.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Brown et al. 2002, Plant Biology; Jones & Jacobsen 2009, Montana State University Extension, Micronutrients Full references

    • Molybdenum: what it does

      Turns nitrate into protein. Looks like nitrogen deficiency on a soil that has nitrogen.

      Sources: Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 7; McCauley, Jones & Jacobsen 2011, Montana State University Extension, Plant Nutrient Functions and Deficiency and Toxicity Symptoms; Jones & Jacobsen 2009, Montana State University Extension, Micronutrients; Roberts & Morton (eds) 2023, Fertiliser Use on New Zealand Dairy Farms Full references

    • Silicon: what it does

      Hardens cell walls and stems, resists mildew and stress. Build it in early.

      Sources: Epstein 1999, Annual Review of Plant Physiology and Plant Molecular Biology; Marschner 2012, Marschner's Mineral Nutrition of Higher Plants, 3rd edn, ch. 8 Full references