If you’ve ever worked with plants—whether you’re a hobbyist tending veggies on your patio, a small-scale nursery growing ornamental shrubs, or a crop farmer chasing that perfect yield—you know temperature is the silent boss. It messes with everything: germination, flowering, fruit set, even how much water plants drink. And if you’re using plant-derived PGRs (growth regulators), you might’ve wondered: do these natural, plant-based goodies get thrown off by temperature too? Plant-Derived PGR
Full transparency here—we’re the folks who make these plant-derived PGRs, so this isn’t just a random science rant. We’ve had hundreds of growers hit us up asking this exact question over the last few years, and honestly, it’s 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’re all plant people who live for this stuff).
First, let’s break down what we’re actually talking about when we say “plant-derived PGRs.” A lot of people mix these up with synthetic PGRs—those lab-made ones that have been around forever, like some of the old stuff that’d make you side-eye if you’ve 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’re the same molecules plants already use to tell each other what to do—no weird synthetic frills, which is why they’re so popular with organic growers and anyone trying to keep their garden or farm as natural as possible.
Now, the core question: do temps mess with how these work? Short answer? Yes—but not in the one-note way you might think. It’s not like “hot temp = bad, cold temp = good.” It’s way more nuanced, and it depends on three big things: which PGR you’re using, what temp range we’re talking about, and what plant you’re spraying it on.
Let’s start with the lab basics, because that’s where we got our first clues. Plant-derived PGRs aren’t static molecules. They’re organic compounds, so their structure can shift when temperatures swing too far. For example, auxins—super common, used to promote root growth or prevent fruit drop—have a molecular structure that breaks down if it gets too hot, like over 95°F (35°C) 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°F by noon, and only 30% of the roots formed properly, compared to 85% when we kept the greenhouse between 70–80°F (21–27°C). But here’s the weird part: cold temps aren’t great either. If it’s below 50°F (10°C), auxins slow way down—plants don’t 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—he sprayed our auxin product in early spring when nighttime temps were 45°F, and his pumpkins ended up with weirdly stunted leaves because the auxin didn’t break down like it was supposed to.
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—around 75–85°F (24–29°C). When it’s under 60°F (15°C), gibberellins take twice as long to kick in, and if it’s over 90°F (32°C), 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°F, the heads were 15% smaller than when we sprayed it in May when highs were 78°F. But here’s the pro tip we figured out: if you’re 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.
Cytokinins are the PGR for cell division—used 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: 65–80°F (18–27°C). We noticed if temps spike above 85°F when we apply cytokinins, some of the active compounds bind to things in the spray water and don’t get absorbed by the plant as well. A strawberry grower in Florida hit us up about this last season—he 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°F, and he said his next spray had 20% more buds, no lie.
Brassinosteroids, the newer kid on the plant-derived PGR block, are super versatile—they help with stress tolerance, like drought or heat, and they boost growth. We were surprised to find they’re actually more resilient to temp swings than the others, but they still have a range. They work best between 55–85°F (13–29°C); above 90°F, they start to break down, but if you’re 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’s a thing—May 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’s stress response in both hot and cold, as long as you apply them when the temp isn’t extreme.
Wait, but a lot of you might be thinking: “What if I’m not spraying them? What if I’m amending the soil with a plant-derived PGR granule?” Oh, great question—we sell those too, because some growers prefer soil applications over foliar sprays. Soil-applied PGRs have a different temp factor because they’re in the soil, not on the leaf. Soil temps: if it’s below 50°F (10°C), 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°F (29°C), 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°F, 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.
Now, here’s the thing we want to make clear: this isn’t a “don’t use plant-derived PGRs when it’s hot or cold” warning. It’s a “work with the temp, not against it” 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’re gentle, they match the plant’s natural cycle, so adjusting your application based on temp is just part of using them effectively, not a flaw.
We’ve put together a little cheat sheet for our regular customers, but here’s a quick breakdown for anyone reading this:
- Foliar sprays: Apply early morning, when temps are between 60–85°F (15–29°C), avoid midday heat.
- Soil granules: Apply when soil temps are 55–80°F (13–27°C), water in immediately to prevent leaching.
- If you have to spray in hotter or colder temps than ideal, cut the dosage by 25%—that’s a trick we learned from our agronomist team that works way better than cranking up the dose.
Wait, and let’s address a myth we hear all the time: “Since these are plant-derived, they work the same no matter what temp.” No way. Plants don’t work the same in extreme temps, so why would the molecules that regulate them? It’s like if you try to bake a cake in a freezer—even if the recipe uses the same ingredients, the temp changes how it turns out. Same with PGRs.
We also did our own storage tests, because temp affects them before you even use them. If you store our plant-derived PGRs in a garage that hits 100°F in summer, half the active ingredients are gone in 3 months. If you store them in a cool, dark place (like a pantry, not the back of your truck), they stay good for 12+ months. That’s a simple tip that makes a huge difference—we printed that on every product label, but a lot of people miss it.
At the end of the day, we started this company because we were tired of seeing growers use synthetic PGRs that messed up their soil, their plants, and the beneficial bugs they worked so hard to attract. Plant-derived PGRs are the future, but only if we use them right. Temperature is just one piece of the puzzle, but it’s a big one. If you’re struggling with a spray that’s not working as expected, or you want to adjust your application for the temp where you are, hit us up—we’ve got agronomists on staff who will chat with you for free, no sales pitch, just real advice based on what’s worked for hundreds of growers like you. Whether you’re growing in a small backyard or a 100-acre farm, we’re here to help you use our plant-derived PGRs to get the results you want, without the weird synthetic stuff.
Don’t overcomplicate it—temp doesn’t have to be a enemy. A little adjustment, a little planning, and our plant-derived PGRs will work exactly how they’re supposed to, no matter what your weather throws at you.
Plant Growth Regulators References
- Clouse, S. D., & Sasse, J. M. (1998). Brassinosteroids: Essential regulators of plant growth and development. Annual Review of Plant Physiology and Plant Molecular Biology.
- Davies, P. J. (Ed.). (2010). Plant hormones: Physiology, biochemistry and molecular biology. Springer.
- Kozuka, T., et al. (2010). High temperature-induced hypocotyl elongation is mediated by auxin in Arabidopsis. Plant and Cell Physiology.
- Rademacher, W. (2015). Plant growth regulators: Classification and uses. Journal of Plant Growth Regulation.
- Taiz, L., et al. (2020). Plant physiology and development (6th ed.). Sinauer Associates.
Grow Plus Crop Protection Co., Ltd.
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