Dealing with the scorching sun has been a very testing time for me as I monitored the growth of my young bonsai tree collection.
Without any clouds or rain to give us a break in this recent three week heat wave, even the native trees outside seem to be having a hard time adapting to the unusually hot weather.
This is a post I have been putting off for a while, because frankly I didn't want to show photos of my bonsai trees all looking miserable with their leaves falling off and their branches looking Kentucky fried. For me it is a learning process. I have to find out what works for my trees, and my trees have to undergo a process to begin to adapt to the conditions around them. It takes time.
Now that some of my trees are starting to recover, and I have found some solutions that seem to be working, I am happy to share some of the results. Maybe other hobbyists can benefit from my experiences.
Enjoy.
Heat Stress
Let's look at a list of signs that a tree might be suffering from some kind of heat stress.
This is kind of a no-brainer, but if you notice any of the following symptoms suddenly affecting your trees, it probably needs some extra tender loving care.
- Leaves turning pale yellow, bright yellow, or brown.
- Leaves becoming crispy, crumbly, brittle, shattered.
- Leaves falling off.
- Trees with large, thick leaves getting a rusty looking tan, as if getting sunburned.
- Branches wrinkling.
- Branches turning black or gray.
- Branch tips becoming brittle, thin, and snapping off.
- New leaves and stems are turning brown and yellow.
- New leaves and stems are sagging downward, looking weak.
- Soil is drying out after it has already been watered that day.
Why is too much sun bad for trees?
Usually full sun is great for trees. For bonsai trees, they are not as healthy as a full grown tree with long deep roots, and so they need a lot more attention to maintain their health during extreme weather conditions.
If a tree exhibits any of the above symptoms it could be for various reasons.
- The light of the sun radiation is too strong.
- The air might be too dry and hot, causing water to evaporate quickly.
- The pot absorbs too much heat, and doesn't release heat well.
- The hot, damp soil might be steam cooking the roots.
- The tree has gone into shock mode, and will die back excess mass it cannot support.
- Poor air quality, air pollution, high elevation, and ozone atmosphere depletion.
Three Best Solutions
1. Shade, shade, shade.
Putting my trees into a shady area under the tall trees near the side of our house has been a life saver for my trees. Two weeks in the shade, and my trees are already starting to show new signs of growth. All the new cuttings are showing signs of terrific new growth.
In the shade, my trees don't need to be watered daily if they have enough shade. The soil stays cool, and retains plenty of moisture for the next day. The leaves are staying healthy green. Growth is able to resume as soon as balance has been restored to the root/soil zone inside the bonsai pot.
2. Sunscreen?
This is a strange idea to consider, and not one used or recommended in traditional bonsai schools. A generous coating of petroleum jelly (vaseline works great) massaged onto the trunk, bark, and stems of a tree will offer the tree many benefits.
- Locks moisture under the oily surface.
- Reflects harmful light rays off the branch surfaces.
- Channels locked surface water towards the pores on stems to feed leaves.
- Humid air surface coats the tree. Trees love moist air.
- Water stays cooler than outside air because harmful radiation is blocked.
- Thick jelly provides insulation from the hot air outside, keeping the tree cooler.
See the shiney stems? I think it looks more healthy with the shiney appearance.
Make sure you don't drip the Vaseline onto the soil and roots. The sticky, oily layers might ruin the bonsai soil, because the fine root hairs need to be able to reach and grab into the dry pocket crevices of the rocks and sand so they can feed on the dew that form there. An oily soil surface would shed water, and possibly disrupt the tree's ability to absorb water from the roots.
3. Bath
I grow many different Willow trees. Pussywillow and Curly Willow, and they are both trees that tend to grow near ponds in nature. They are used to having their roots with wet feet.
Don't be afraid to put a dish of shallow water under the pots, to fully submerge the base of the pot. Make it easy for the soil to wick the water instantly into the pot to feed the tree roots.
As long as you are using a light colored dish, water should evaporate from it before it gets too hot, and the loose water under the bottom of the bonsai pots will also be cooler because it is being shaded from the sun.
I am usually satisfied if the water evaporates from the dish by sunset, because it means that my trees had access to fresh water all day long.
Emergency Solution: Soil Change
This is how I grow my new tree cuttings, in a small basin of mostly sand, pumice, small gravel lava rocks.
Some of my trees I noticed were having a hard time in the pots they were in. When I touched the soil, it was very damp, and very hot. The pots they were in were made out of cheaper nursery store plastic, and the soil was mostly cheap potting soil. Imagine trying to relax with a thermal blanket wrapped tightly around you while in a hot sauna. That is probably what it feels like for a plant or tree stuck inside a small plastic pot on a hot day. Microwave!
Move to a shaded area, and carefully unroot any suffering trees from their pot, and replant them gently inside a deep basin of sand and small rocks. Spray with water to coat the rocks with moisture, leaving a shallow 1/4 inch of water along the base.
This method provides a much cooler soil environment for the roots to relax into. Keep it in a shaded area if possible outside. I actually leave my cuttings in the full sun, and the rocks and sand seem to offer enough protection to keep the trees growing.
For trees that are struggling really bad, on death's door
Fill a bucket half deep with rocks and sand, and bury the tree much deeper than normal, even all the way up the trunk, allowing only the branches and leaves to stay above the surface. This will help allow the water to get into the pores of the branches, so they can swell up with new life and vigor to grow. The sides of the bucket rim will also give the tree some added shade. Pick a light color of bucket if possible, or bury the bucket in a deep hole, to allow the earth to insulate it, keeping it cooler.
Some people even dig a hole, and bury the tree right in. If you do it that way though, you might have to dig out, and cut off, any long tap roots that form when you eventually transplant the tree back into a pot. Otherwise it might become a permanent tree growing in your yard.
Results
Below is one of the trees I was most worried about. It lost all of its leaves. Now it is recovering quickly. The branches have swollen and turned green again.
New buds are forming around the base of the branches.
Also my hydrangea cuttings had leaves that all became crispy dry, but now they are starting to form new buds.
Those buds are forming directly in the midpoint of those long stems that were growing like long stick before the heatwave came. Now I am really happy where those buds started forming. That is where I was thinking of pruning them in the winter, to keep the branches smaller.
Surprise Bonus
Wouldn't it be awesome to grow hydrangeas that look like this?
These are flowers I found while out walking the neighborhood. This is the nicest blend of colors I have found so far on a hydrangea. I wonder if they can be grafted onto one of mine. Rooting the cuttings were pretty easy to do.
Bonsai!
Wednesday, July 8, 2018
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