by Lee Squires

I have been washing the roots of my bonsai since 1972 when I first started to grow bonsai. This is a great technique to use for two main reasons. All of the old, original soil can be removed without root damage and you can see the entire root system and make some initial root removal cuts.

Some of the trees you may select as a bonsai target could have been growing in the ground in a nursery situation. These trees will have "real" soil all around the root system. If this soil is not completely removed at the first potting, it will impede drainage and cause root rot in a container growing situation sometime in the future. Drainage may be fine near the edge of the container where bonsai soil was used in transplanting but where old soil was not removed near the trunk, roots will start to die back over time.

The best way to wash roots is with a trigger-type nozzle on a hose. Hold the trunk of the tree and apply the necessary water pressure to wash the soil off of the roots. I, generally, start from the top of the root ball and blow out the soil starting at the trunk and work toward the root tips. Then, I turn the tree on its side and wash the soil from the bottom of the root mass. After this is done, the tree can be potted with a granular soil mix, and the soil particles will sift easily into the entire root zone. This will give the entire root system equal amounts soil, water and oxygen to prevent root rot and promote extensive healthy root growth. Roots will grow prolifically near the trunk and not just at the perimeter of the root mass. Removing all of the soil at one time can be done with deciduous trees; evergreens are a different story.

The old soil around the roots of evergreens should be removed in two steps: half of the soil should be washed away with the first transplanting and the other half should be washed away at the second transplanting in a couple of years. There are two reasons for this: evergreens should not really be bare-rooted and total root washing at one time removes too much of the mycorrhiza (friendly fungus). What I generally do is wash out the heavy soil near the trunk and remove some of the soil at the mid and perimeter sections of the root zone with a chopstick leaving some of the old soil. Then, I pot with bonsai soil and sift the particles into the root zone as much as possible.

Another good opportunity for root washing is to wash after a tree has been potted for several years. In most cases, the tree's root system is severely dense and choked out near the trunk even though bonsai soil was used and most of the soil in the interior of the root mass has disintegrated and drainage has slowed down to a crawl. You can easily pull the tree out of the pot and train a strong stream of water on the root ball and remove a lot of the old bonsai soil. New air pockets are opened up, fresh soil can be introduced and roots will flourish in areas that had been devoid of new roots for a few years. In these cases, around 75% of evergreen roots can be washed without hurting the tree because they have been growing in pot culture for a number of years. Actually, removing old soil with a chopstick causes more damage than water because of the pulling and tearing action of the chopstick.

When potting season arrives you should be ready to try this technique and improve your tree's health and create a "happy zone" in the subterranean environment where your tree's roots live.