We are in the thick of winter, so let’s run through some of the marketing bollo*** that lands in your inbox every year as companies try to drum up sales in their low season for foliar fertilisers. A lot of it starts from real plant science, then quietly stretches that science into promises the products cannot keep.
Before you buy any winter liquid, put every claim through three questions:
- Is there a plausible biological mechanism?
- Is there a measurable turf response?
- Is there a noticeable improvement on the ground?
Most claims pass the first, some pass the second, and very few pass the third. Here are the ones you will hear this month.
1. Phosphorus in cold soils
The science is sound. Phosphorus moves to the root by diffusion, and cold soil slows diffusion, slows the microbes that release it, and slows the root’s ability to take it up. So a cold soil can hold plenty of P that the plant struggles to reach.
Where it gets stretched is the jump to “so spray foliar P and grow winter roots.” Two problems. You can only get a tiny amount of P through a leaf in a single pass, nowhere near enough to feed a whole-plant shortfall. And correcting a genuine deficiency is not the same as adding root growth to turf that is already fed. Fix a real deficiency and you will see a response. Spray P over an adequately fed turf cover and you are mostly spending money.
Verdict: real mechanism, small field response.
2. Calcium and “stronger, wear-tolerant turf”
Calcium does build cell walls, along with silicon and boron. That’s true. But this wall-strengthening only happens on new growth, and in cold weather the plant barely grows. You cannot strengthen tissue the plant is not building.
The “foliar calcium bypasses poor movement in the plant” argument comes from fruit and vegetable crops, where locked-away tissues like the inside of a tomato genuinely miss out. Turf is almost all leaf, and leaves get calcium through normal water movement. Even where foliar calcium does land, it stays near the leaf and does very little for crowns, stolons or roots. So take any whole-plant “strengthening” claims with a pinch of salt.
And while we are at it don’t let silica be sold to you as a way to increase turf wear tolerance. A granular Ca/Mg-silicate worked into the rootzone across a season did lift canopy quality on a worn ryegrass field, but that also applied calcium and magnesium, so you cannot pin the response on the silicon (Pruyne, Schlossberg & Uddin 2019).
On seashore paspalum, foliar silicon did nothing for wear. Low rates of foliar silicon gave no increase in wear tolerance or quality, and only a high-rate soil drench gave any benefit at all (Trenholm et al. 2001). Increasing leaf silicon with a spray is easy, but there is no proof it actually increases wear tolerance.
Verdict: growth-limited in winter, whole-plant claims overstated.
3. Sugars, carbon and “enzymes”
The thing limiting winter growth is temperature, not a lack of carbon. Cold slows the plant’s enzymes and metabolism, and pouring on sugars or organic acids does not switch that back on.
“Contains plant enzymes” is the weakest claim in the category. Unless the label names the enzyme, its activity, and its stability, the word means nothing. Most enzymes sprayed onto turf are proteins that break down fast in the field and cannot get inside plant cells anyway.
There is one honest version of the carbon story, and it is in the soil, not the plan. If you feed carbon to the soil it can increase microbial activity and nutrient cycling. That is a soil effect, and marketing routinely sells it as if it were feeding the grass directly. Worth a caution from our own side of the fence as well: in a replicated pot trial, 2,3-butanediol applied on its own actually lowered colour, but earns its keep as a root stimulant-in another product (Spencer 2026). A fashionable carbon input can do nothing, or even worse, on its own.
Verdict: real soil biology, oversold as plant energy.
4. Amino acids and “stress hormones”
Amino acids have a genuine basis. Turf can take some up directly, which can save it a little energy under stress, with modest gains in nitrogen use and stress tolerance. Modest is the operative word.
“Supplies stress hormones” is a different matter. Cold-stress physiology runs on specific compounds (ABA, salicylic acid, jasmonic acid and others) that act at precise, dose-dependent levels. Without naming the compound, its concentration and its stability, “stress hormones” on a label is marketing, not chemistry.
That cuts both ways, and we hold our own products to it. Where one of ours does not clear the bar we say so: the butanediol above is ours, and on its own it failed as improve turf colour in that trial.
Salicylic acid earns its place in our formulations only because it can be pinned down, a named compound at a stated rate with stability data, a claim you can test the same way I am asking you to test every other label.
Verdict: amino acids modest and real, generic “hormones” not a claim at all.
5. Potassium in wet soils
Potassium matters for water relations and enzyme function. But “wet soil cuts potassium uptake” oversimplifies. It can be true on a saturated, leaching sand with low reserves. On a soil with holding capacity and adequate potassium, it usually is not. The claim confuses slower delivery with actual deficiency.
Verdict: situational, not a blanket rule. Test before you treat.
6. Iron, manganese and zinc
These are real nutrients with real jobs. But the idea that winter colour loss is a trace-element shortage is usually wrong. Winter yellowing is mostly cold shutting down chlorophyll production, and cold-driven purpling is a pigment response, not a deficiency.
Foliar iron does green turf up fast, but that is either fixing a real shortage or simply iron darkening the leaf. Neither means more photosynthesis. And the colour does not last: iron is immobile in the grass and leaves with the clippings, so published turf work puts the foliar response at a few weeks at most, and shorter in cold (Shaddox & Unruh 2018). Useful as cosmetics, not proof of a healthier plant.
Verdict: quick colour, not a health gain.
What actually drives winter turf
In roughly this order:
- Soil temperature
- Light
- Water management
- Traffic
- Nitrogen
- Root-zone oxygen
- Potassium
- Micronutrients
- Biostimulants
Specialty liquids live near the bottom. They fine-tune a good programme. They do not rescue a bad one.
The question the labels never answer
Almost every claim is qualitative. “Improves uptake.” “Supports resilience.” None of it tells you how much. The honest question is: what improvement should I actually expect in the field? When there is a number, it is usually small: foliar iron colour lasts a few weeks at most, amino-acid gains run to low single-digit percentages, and independent standalone biostimulant trials often come back with no response (Spencer & Smith 2021).
Weight the evidence that companies put in front of you too. Independent replicated field trials beat manufacturer trials, which beat glasshouse pots, which beat “mechanism suggests.” Most specialty claims live at the bottom of that ladder.
Before you buy
- Does a soil or tissue test confirm the deficiency you are treating?
- Is the rate meaningful against published dose-response work?
- Are there independent field trials on your species and soil?
- What does it cost per unit of active versus a conventional source?
Liquid specialty products have a real place in a well-built programme. Their value is as precision top-ups, not as the answer to winter stress. Start with temperature, light, water and traffic. Reach for the bottle last.
Do foliar biostimulants work on turf in winter?
They can help at the margins but rarely as marketed. Independent standalone field trials on turf often show no measurable response. Their value is as a precision top-up within a sound programme, not as a primary fix for winter stress.
Does foliar iron improve winter turf health?
Foliar iron greens turf fast, but that is either correcting a deficiency or an iron film darkening the leaf. It is not proof of more photosynthesis, and the colour lasts only a few weeks, shorter in cold. It is cosmetic, not a health gain.
Will spraying foliar phosphorus grow winter roots?
Cold soil does limit phosphorus uptake, but the amount deliverable through a leaf is tiny. Correcting a real deficiency gives a response; spraying phosphorus over adequately fed turf mostly wastes money.
Does silicon improve turf wear tolerance?
Only from whole-rootzone silicate products, and even then the benefit tracks the accompanying calcium, magnesium or potassium, not the silicon itself. Foliar silicon shows no demonstrated wear payoff.
Further Reading
- Turf nutrient management: foliar versus soil uptake
- Biostimulants for turf: what the evidence actually shows
- Potassium fertiliser strategy for turf
- Organic fertilisers, soil carbon and Poa annua
- Traffic and wear stress on sports turf
- Plan inputs on evidence with GAIP Hub
References
- Pruyne, Schlossberg & Uddin (2019), Agronomy 9(10):578, granular Ca/Mg-silicate and ryegrass wear.
- Trenholm et al. (2001), J. Plant Nutr. 24:245–259, potassium silicate on paspalum (foliar Si did nothing, only a high-rate drench helped, and even there the silicon effect is hard to isolate);
- Shaddox & Unruh (2018), UF/IFAS EDIS ENH1287, iron for turfgrasses;
- Spencer & Smith (2021), Bonnie Doon trial;
- Spencer (2026), butanediol trial.
Jerry Spencer is Principal Agronomist at Gilba Solutions, an independent turf and soil consultancy based in the Southern Highlands, NSW.
Principal agronomist, Gilba Solutions Pty Ltd
BSc Hons Soil Science (Newcastle). Former STRI agronomist. Author of Nutrition of Sports Turf in Australia (CSIRO/Landlinks Press). 35+ years advising on sports turf, golf and stadia across Australia, NZ, UK and Europe.