AusBonsai

I’ve heard a lot of conflicting stories in my time about repotting natives in 40 plus heat, and the dos and donts.
So basically I just wanted to experiment for myself how it went.

From what a lot of people have said is that it isn’t recommended and if it has to be done, to place the repotted tree out of direct heat or into shade.
Others say it’s the lack of water that kills the tree if left unattended and to go ahead and repot.

Well.... the last weekend that just went, was one hell of a hot weekend. Over 40s and windy too.

Now, I didn’t just use already repotted trees, I’m talking about full on nursery stock, and never had their roots cut.

I attempted this with 2 casuarinas, a baeckea and a calathamnus

There was root removal involved and removal of a moderate amount of foliage, but no trunk reduction. They were placed right back into the direct sun that they were in before, after the repot.

They were well watered and had about 40% washed River sand applied to the potting mix. During the repot, I made sure the roots were all continually sprayed gently with water to keep them wet.

It’s been a week, and they look the same as they did before the repot. It’s not very scientific, but it certainly has leaned my mind towards the philosophy of:

It’s not the heat, but the lack of water that kills trees during or after a repot. Again, it’s probably not the same for all species, but so far it’s interesting that not one of them has shown any signs of distress.

Thanks for going out on a limb and doing the trials Rory. Give it a little longer to see what happens but you have just replicated what I have found for the past couple of years. High temp is no barrier to repotting natives.

Expect many of the experienced growers to have closed minds on this but hopefully we present some of the newer people with the real truth.

Hi Rory ,I had several pots blow over ,including a smashed one on that weekend. A quick repot, inluding cutting back of the roots as had been exposed a fair time and back out enjoying the sunshine . As you say keep up the water and things should be fine. Cheers John.

Thanks Rory, really interesting observations.

It’s not the heat, but the lack of water that kills trees during or after a repot.

i believe in this too. Satsuki are repotted after flowering because it's monsoon season, lots of rain.

All trees shut down if temperatures go over or under a certain temperatures(tree dependant). The real trouble occurs when the temperate falls / rises and the trees need fluid and they have minimal roots to take that fluid up. In Sydney I have seen way too many pines killed / burnt because the roots were pruned in September and October had had a high 30 degree day/days and the needles could not get enough fluid to stay green. Aftercare is dependant on the experience of the Bonsai artist
Nurseries always have to repot when possible but even they try and avoid high temperature days. Not a good practice for beginners to take note of.

My post was about natives. I haven’t grown exotics for a long time, but I have never found that I would lose trees because of repotting in 40 degree days.
To me your post doesn’t make sense. A tree needs water whether it’s summer or winter. Trees can die quickly in winter if you underestimate the wind and the lack of time between waterings too. But I have literally repotted 100s of banksia / Eucs / Callistemon / casuarina / leptospermum / melaleuca etc etc.... and all throughout blazing summer days and the only time I would lose material would usually be if I worked roots too hard (regardless of the season).
The heat during a repot has not ever played a factor in my repots, and I’ve always placed them right back into full sun.

The point of this post was to prove what I feel is an old wives tale, is wrong.

If you remove a tonne of root my friend, it doesn’t matter what the temps are.... you’re walking a thin line. The heat is not going to stop the uptake of water to the tree simply because it’s hotter. In fact, I find on a hot day, if the tree is wilting from lack of water in the pot, and you thoroughly water the tree, the ends will regain rigidness quicker than if you do this in winter because it flows quicker in the warmer months.

The reason you often might see a tree in distress after a repot is because you’re removing too much root and leaving too much branching on the tree so the tree can’t maintain the balance. But this rarely kills a native. Provided you’ve not severely damaged the entire root system and merely reduced it... the tree will simply die back to a level that the roots can now support.
Again, nothing to do with the high levels of heat.

barefoot wrote: ↑December 4th, 2020, 8:24 pm In Sydney I have seen way too many pines killed / burnt because the roots were pruned in September and October had had a high 30 degree day/days and the needles could not get enough fluid to stay green.

More relevant than heat is going to be relative humidity and wind. Low humidity and high wind will result in a higher transpiration rate, and therefore more work for the roots to do.

When repotting in high temperatures or windy conditions I often soak a cloth in water and drape it over the root ball if there is any delay in getting the tree back into soil, even if it is only for 10 minutes. It also helps if the tree has been soaked well before the repot. I've never lost a tree because it was repotted in hot weather.