Over the years I’ve heard a lot of admonitions about watering carefully in summer. And for good reason – trees can dry out quickly when its warm out. At a glance, it looked like most of my trees were over watered as moss was beginning to develop.
Green soil – a sign that the soil has been wet lately
This didn’t totally make sense to me. I’m used to trees drying out at a certain rate and seeing green soil made me question the assumption that green means wet. I investigated.
Removing surface soil with bent nose tweezers
It turns out that the soil was fairly dry and the tree in need of water. What happened?
Some cool weather a few weeks back meant that the the soil on my trees dried out slowly. Moss started to grow. When it warmed up, the soil stayed green, making it hard, at a glance, to tell if my trees needed water. In the case of this pine planting, I removed all of the old surface soil and added some new soil.
Old surface soil removed
Top dressing added – lava and akadama
After adding the top dressing, I watered the trees and added some new fertilizer.
Piles of cottonseed meal
I found similar cases on a number of trees, including the black pine below. After removing the surface soil, I added top dressing and watered the tree.
Old soil – dark from decomposed fertilizer and new moss
Surface soil removed
Top dressing added
My small azalea showed more signs of moisture – healthy moss growing on the surface of the soil. Was the soil here wet or dry?
Beneath the moss – wet soil
The azalea soil was quite moist. After placing the shohin tree on a bed of lava (see “Keeping bonsai from drying out in summer“) I’ve had a much easier time keeping it from drying out. I performed soji anyway (see “Summer Soji“) and added white sphagnum moss to retain extra moisture.
White sphagnum moss
Next I looked at my hornbeam. Surely this tree was getting enough water?
Old soil on a Korean hornbeam
I removed the surface soil and found yet another dry tree.
Healthy hornbeams are thirsty trees, and the pot in this case is on the small side. I removed the surface soil, added fresh soil, and covered this with white sphagnum to help retain moisture.
White sphagnum top dressing
I’ve since checked all but a few of my trees, cleaning a lot of the old soil that made watering tricky. Now it’s easier to tell which trees need more water, and which need less. Thinking how nice it would be to be around enough to water each tree when it needed it, I again realized a key benefit to the apprentice system.