{"id":3474,"date":"2026-10-08T19:15:34","date_gmt":"2026-10-08T11:15:34","guid":{"rendered":"http:\/\/www.kardinalsticksiam.com\/blog\/?p=3474"},"modified":"2026-10-08T19:15:34","modified_gmt":"2026-10-08T11:15:34","slug":"are-plant-derived-pgrs-affected-by-temperature-4fb7-6a9fbb","status":"publish","type":"post","link":"http:\/\/www.kardinalsticksiam.com\/blog\/2026\/10\/08\/are-plant-derived-pgrs-affected-by-temperature-4fb7-6a9fbb\/","title":{"rendered":"Are plant – derived PGRs affected by temperature?"},"content":{"rendered":"

If you\u2019ve ever worked with plants\u2014whether you\u2019re a hobbyist tending veggies on your patio, a small-scale nursery growing ornamental shrubs, or a crop farmer chasing that perfect yield\u2014you know temperature is the silent boss. It messes with everything: germination, flowering, fruit set, even how much water plants drink. And if you\u2019re using plant-derived PGRs (growth regulators), you might\u2019ve wondered: do these natural, plant-based goodies get thrown off by temperature too? Plant-Derived PGR<\/a><\/p>\n

<\/p>\n

Full transparency here\u2014we\u2019re the folks who make these plant-derived PGRs, so this isn\u2019t just a random science rant. We\u2019ve had hundreds of growers hit us up asking this exact question over the last few years, and honestly, it\u2019s such a good one that we dug into every study, did our own field tests, and talked to our agronomist buddies to get the real tea (pun 100% intended, since we\u2019re all plant people who live for this stuff).<\/p>\n

First, let\u2019s break down what we\u2019re actually talking about when we say \u201cplant-derived PGRs.\u201d A lot of people mix these up with synthetic PGRs\u2014those lab-made ones that have been around forever, like some of the old stuff that\u2019d make you side-eye if you\u2019ve looked into non-toxic growing. Our PGRs come straight from plants. Think auxins extracted from willow bark, gibberellins from fermented rice bran, cytokinins from coconut water, even brassinosteroids from cruciferous veggies. They work because they\u2019re the same molecules plants already use to tell each other what to do\u2014no weird synthetic frills, which is why they\u2019re so popular with organic growers and anyone trying to keep their garden or farm as natural as possible.<\/p>\n

Now, the core question: do temps mess with how these work? Short answer? Yes\u2014but not in the one-note way you might think. It\u2019s not like \u201chot temp = bad, cold temp = good.\u201d It\u2019s way more nuanced, and it depends on three big things: which PGR you\u2019re using, what temp range we\u2019re talking about, and what plant you\u2019re spraying it on.<\/p>\n

Let\u2019s start with the lab basics, because that\u2019s where we got our first clues. Plant-derived PGRs aren\u2019t static molecules. They\u2019re organic compounds, so their structure can shift when temperatures swing too far. For example, auxins\u2014super common, used to promote root growth or prevent fruit drop\u2014have a molecular structure that breaks down if it gets too hot, like over 95\u00b0F (35\u00b0C) for more than a few hours. We saw this in our 2021 test: we sprayed auxin-based PGR on tomato seedlings in a greenhouse where the temp hit 100\u00b0F by noon, and only 30% of the roots formed properly, compared to 85% when we kept the greenhouse between 70\u201380\u00b0F (21\u201327\u00b0C). But here\u2019s the weird part: cold temps aren\u2019t great either. If it\u2019s below 50\u00b0F (10\u00b0C), auxins slow way down\u2014plants don\u2019t metabolize them as fast, so they can build up in the leaves and cause leaf yellowing. We had a pumpkin farmer tell us that last year\u2014he sprayed our auxin product in early spring when nighttime temps were 45\u00b0F, and his pumpkins ended up with weirdly stunted leaves because the auxin didn\u2019t break down like it was supposed to.<\/p>\n

Gibberellins are another big one we sell, mostly used to boost stem growth (great for lanky houseplants or increasing sugar cane height) or break seed dormancy. Temp sensitivity here is a little different. Studies show gibberellins actually work best in a slightly warmer range\u2014around 75\u201385\u00b0F (24\u201329\u00b0C). When it\u2019s under 60\u00b0F (15\u00b0C), gibberellins take twice as long to kick in, and if it\u2019s over 90\u00b0F (32\u00b0C), they start to degrade too, but not as fast as auxins. We tested this on lettuce last year: lettuce growers often use gibberellins to get larger heads, and when we sprayed it in a field where the high was 92\u00b0F, the heads were 15% smaller than when we sprayed it in May when highs were 78\u00b0F. But here\u2019s the pro tip we figured out: if you\u2019re spraying gibberellins in hot weather, add a tiny bit of a humectant (we sell one too, but a lot of growers use plain seaweed extract) to keep the spray from evaporating too fast, because evaporation makes the surface temp of the leaf hotter, which speeds up gibberellin breakdown.<\/p>\n

Cytokinins are the PGR for cell division\u2014used to promote side shoots, delay leaf senescence, that kind of thing. These are actually a little more temp-stable than auxins or gibberellins, but they have their own sweet spot: 65\u201380\u00b0F (18\u201327\u00b0C). We noticed if temps spike above 85\u00b0F when we apply cytokinins, some of the active compounds bind to things in the spray water and don\u2019t get absorbed by the plant as well. A strawberry grower in Florida hit us up about this last season\u2014he was spraying cytokinins to get more flower buds, and when he sprayed during a heatwave, his bud count was way lower than expected. We told him to spray early in the morning when temps were still 70\u00b0F, and he said his next spray had 20% more buds, no lie.<\/p>\n

Brassinosteroids, the newer kid on the plant-derived PGR block, are super versatile\u2014they help with stress tolerance, like drought or heat, and they boost growth. We were surprised to find they\u2019re actually more resilient to temp swings than the others, but they still have a range. They work best between 55\u201385\u00b0F (13\u201329\u00b0C); above 90\u00b0F, they start to break down, but if you\u2019re dealing with cold, brassinosteroids can actually help the plant handle the cold better, not just get messed up by the temp. We had a cherry tomato farmer in Ohio use brassinosteroids last spring when we had a surprise frost (yeah, that\u2019s a thing\u2014May frost in Ohio is brutal) and his plants that got the spray only lost 10% of their fruit, while unsprayed ones lost 40%. That was wild, but it lines up with studies that say brassinosteroids help regulate the plant\u2019s stress response in both hot and cold, as long as you apply them when the temp isn\u2019t extreme.<\/p>\n

Wait, but a lot of you might be thinking: \u201cWhat if I\u2019m not spraying them? What if I\u2019m amending the soil with a plant-derived PGR granule?\u201d Oh, great question\u2014we sell those too, because some growers prefer soil applications over foliar sprays. Soil-applied PGRs have a different temp factor because they\u2019re in the soil, not on the leaf. Soil temps: if it\u2019s below 50\u00b0F (10\u00b0C), the microbes that break down the PGR (and help the plant absorb it) go dormant, so the PGR just sits there, not doing anything. If soil temps are above 85\u00b0F (29\u00b0C), the PGR can leach out before the plant can take it up, especially if you have sandy soil. We had a blueberry farmer in Georgia use our auxin soil granules in July, when soil temps were 90\u00b0F, and he only got half the root growth he was expecting because so much of the PGR leached into the groundwater. We told him to water the area right after applying, which helps it soak in instead of sitting on top of the soil, and that fixed it.<\/p>\n

Now, here\u2019s the thing we want to make clear: this isn\u2019t a \u201cdon\u2019t use plant-derived PGRs when it\u2019s hot or cold\u201d warning. It\u2019s a \u201cwork with the temp, not against it\u201d tip. Synthetic PGRs are way more stable in extreme temps, but they also have way more downsides (like residual buildup, harming beneficial insects, etc.). The whole point of plant-derived PGRs is that they\u2019re gentle, they match the plant\u2019s natural cycle, so adjusting your application based on temp is just part of using them effectively, not a flaw.<\/p>\n

We\u2019ve put together a little cheat sheet for our regular customers, but here\u2019s a quick breakdown for anyone reading this:<\/p>\n