Plant Sunscreen: Kaolin Clay
Help your plants get through those hot days
It seems to me that the only weather certainty these days is that when the kids go back to school the temperatures will rise. This week has been no exception. With temps in the high 30s and low 40s it is safe to say that the farm has been sweltering. While many plants growing at this time of year are considered to be ‘heat lovers’ that doesn’t mean that they aren’t set back by full scorching sun and - even worse - blustery northerly winds.
Dahlias, in particular, seem to sulk when the temps get a little too high. Although touted as a heat lover, they do their best when temps are below 30c and they can recover in the cool of an evening with a decent drink.
However, there is a product that can offer a little relief when the temperatures are not on your side: Kaolin Clay.
What is it?
Kaolin Clay is a soft mineral clay used in many industries and for many applications including in cosmetics. You can purchase it as a fine powder that, when added to water, can be sprayed over your plants.
In horticulture it has also been used in orchards as a natural pest preventative.
What does it Do?
It creates a physical barrier over the plant leaves. This can prevent sucking insects from being able to penetrate the leaf, fungal spores from establishing, and also helps to protect against sun damage. The protective layer can also prevent transpiration from the leaves helping the plant to remain hydrated in hot and dry conditions.
My Experience
Since I started growing dahlias my common experience has been that planting time is wet and cold. More often than not this has meant delaying planting, or even digging tubers back out after a particularly heavy rainfall.
This year - not so much.
From November the temperatures rose and by early December temps were well into the 30s.
This was not ideal for the dahlias.
Down here in Victoria we usually get a long warm (but not hot) season where the dahlias can establish themselves. They usually have enough greenery by the time it gets hot so that they can shade their roots and keep them cool.
Knowing that there was a heat wave coming, and not wanting to have to mulch all of my plants, I wanted an alternative that was quick and easy.
That was when I discovered Kaolin Clay in the popular Australian Dahlia Growers Facebook group.
The President of the Australian Dahlia Society, Graeme Davis, had made mention of this product that he used to help his plants cope with heat stress. I figured if it was good enough for his exhibition quality blooms it would be good enough for me, and so I rushed out to the green shed to buy a few kilos.
I couldn’t believe how well it worked.
Typically on a hot day it is best to avoid looking at your dahlias in the middle of the afternoon. Usually they will look quite stroppy, their leaves wilted and stems floppy. This kind of heat stress is not ideal because it can slow down the plant’s growth and also can result in burnt and damaged buds.
With the Kaolin Clay applied my plants did not wilt at all including on days where the temps reached 40c and there were hot, blustery winds.
In fact, coupled with pulse watering, my plants have thrived and started flowering as expected in late January.
Application
Tool: Backpack sprayer
I use the same 16 litre backpack sprayer that I use for my foliar feeding. Whatever sprayer you use, make sure that you give it a really good rinse and flush the nozzle once you have finished spraying to ensure it doesn’t become clogged with the clay residue.
How: Follow the directions
I purchased my Kaolin at Bunnings (it is in the pesticide section) and followed the directions on the packet. In my experience, after using it a few times, it seems to work best when applied in a few thin coats with time to dry in-between, rather than attempting to do a very heavy coat all at once.
Does it Last?
The Clay doesn’t appear to to easily wash off so will withstand light rain. However reapplication will be required as the plant continues to grow.
I have found that now that my plants are much bigger they are better able to withstand the heat so have not needed to use Kaolin since they began to flower.
Cautions and Warnings
As with anything in the garden make sure you are wearing appropriate PPE. While not toxic it can cause some irritation.
You will want to cover as much of the leaf surface as you can for best results, however avoid spraying buds where possible. I found a few flowers opened with speckles of clay on the florets - but it was a very minor thing.
Other Benefit
I had started to notice minor mite damage just before applying the Kaolin Clay. The foliage improved dramatically afterward suggesting it may work to battle mites. I had many lady birds, dragon flies, and parasitic wasps in the patch both before and after spraying so hopefully there was minimal impact on the beneficial insects.
What do you think? Will you use plant sunscreen in your patch?
Thanks for the timely reminder to replace the sprayer I gunked up with poorly-strained foliar feed...do you think you'll try the kaolin on any other plants besides dahlias?