Short answer. Mulder's chart is a circular diagram, attributed to the Dutch soil scientist D. Mulder in the early 1950s, showing which nutrients suppress (antagonise) or help (synergise) each other [7]. It is a good reminder that excess of one nutrient can cause shortage of another. But it is a teaching sketch, not a calculator. A review of 117 published interactions found synergy more often than antagonism; the antagonisms that reliably matter are among the cations (K, Ca, Mg, NH₄, Na), phosphorus with zinc and iron, and iron with manganese [1][6].
What's happening
"Antagonism" covers several different mechanisms that the chart lumps together:
- Competition at root uptake. Ions with similar charge compete for transporters and for the root's charge balance. K⁺, NH₄⁺ and Na⁺ suppress Ca²⁺ and Mg²⁺ uptake; Ca²⁺ suppresses Mg²⁺ [6]. In cannabis, higher K supply was linked to lower Ca and Mg uptake [3], and high ammonium reduced cation uptake and yield [4].
- Precipitation in the root zone or tank. Ca with phosphate or sulfate; Fe with phosphate at high pH. That is chemistry, not physiology, and pH controls most of it (see pH and availability).
- Interference inside the plant. High P is associated with reduced Zn effectiveness and Fe translocation in many crops [6]; Fe and Mn compete; Cu and Zn compete.
- Dilution. Adding a growth-limiting nutrient makes the plant bigger, which lowers the concentration of others in tissue without any real antagonism. Shiponi and Bernstein saw P supply reshape the whole cannabis ionome, partly this way [5].
Rietra et al. reviewed 94 papers describing 117 interactions across all macro- and micronutrients: 43 were synergistic, 17 antagonistic, 35 zero-interaction, the rest non-significant or negative. Antagonistic effects on yield were found most often for divalent cations [1]. The authors also note that the number of studied interactions is low, which makes firm conclusions difficult [1].
The interactions worth knowing
| Excess of | Can suppress | Mechanism | Strength of evidence |
|---|---|---|---|
| K | Mg, Ca | Cation competition | Established [6]; observed in cannabis [3] |
| NH₄⁺ | K, Ca, Mg | Cation competition, root damage | Established [6]; cannabis [4] |
| Ca | Mg, (K) | Cation competition | Established [6] |
| Na | K, Ca | Cation competition, membrane displacement | Established [6] |
| P | Zn, Fe, (Cu) | Precipitation and in-plant interference | Supported in crops [6]; untested in cannabis |
| Fe | Mn (and the reverse) | Uptake competition | Supported [6] |
| Cu, Zn | Fe | Competition | Supported [6] |
| N (adequate) | Most others improve | Synergy via growth | Established [1] |
| High bicarbonate/pH | Fe, Mn, Zn, Cu, B, P | Solubility, not antagonism | Established; see pH and availability |
How to use this
- Keep ratios sensible. A standard Hoagland-type solution runs roughly K 235, Ca 200, Mg 49 mg/L (K:Ca:Mg ≈ 1.2:1:0.25). Big departures from that, especially K far above Ca, are where antagonism bites.
- Fix pH before any "lockout" theory. Most so-called lockout is pH or root-zone failure.
- Don't stack boosters. A PK booster plus a bloom base plus Cal-Mag can push K, P and Ca far beyond need.
- Confirm with numbers. Runoff EC, a lab solution test, or a leaf tissue test beat reading a wheel.
Common mistakes
- Treating Mulder's chart as quantitative. It has no doses.
- Calling every deficiency "lockout" and flushing with plain water, which removes everything. A root-zone flush is for real salt build-up (runoff EC far above input), done with a light solution in soilless media (see the flush debate).
- Ignoring dilution when reading tissue tests.
Evidence
- Cation antagonism (K/NH₄/Na vs Ca/Mg): Established in plant nutrition [6], Supported in cannabis [3][4].
- Synergism being more common than antagonism in yield studies: Supported (one large review [1]).
- Mulder's chart as a diagnostic tool: Grower practice; origin detailsbeing reviewed
- Fageria 2001 citation detailsbeing reviewed
Mulder's chart is a diagram showing antagonistic and synergistic interactions between plant nutrients, used as a rough guide to which excesses cause which deficiencies.Nutrient antagonism is when an excess of one element reduces the uptake or use of another, such as high potassium suppressing magnesium and calcium.Ammonium (NH4+) is the positively charged form of nitrogen; a small share stabilises root-zone pH, but too much reduces cannabis yield and quality.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.Phosphate is the ionic form in which plants absorb phosphorus, mainly H2PO4- at the normal root-zone pH of 5.5-6.5.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.A micronutrient is an essential element plants need only in trace amounts, below a few mg/L: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel.Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake.A bloom booster is a high-phosphorus, high-potassium additive sold for flowering; cannabis trials show a P plateau, so past moderate levels it adds cost and runoff, not yield.Cal-Mag is a supplement supplying calcium and magnesium, usually as nitrates; need depends on cultivar, water source (RO vs tap) and medium (coco), not on LED lighting.Runoff EC is the conductivity of solution draining from the pot; compared with input EC, it shows whether salts are building up or being used up in the root zone.A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed.Running a large volume of low-EC water or mild solution through the medium to wash out accumulated salts; it treats the medium, not the plant, and suits any stage.Salt build-up is the accumulation of unused fertiliser and water salts in the growing medium, raising root-zone EC and causing osmotic stress and lockout-type symptoms.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.
