Washing Tree Roots Before Planting

In a previous post I described the right way to plant a tree or shrub. If you follow that process you will have success most of the time. Today, I’d like to look at a new method for treating trees before planting; washing and pruning roots.

Science does not stand still. Tree researchers are continually looking at ways to improve the planting process and in recent years a new way of handling the tree roots has come to light. It goes against everything that makes common sense, but it could have some benefits.

Root Ball Problems

Before I describe the new way method of washing roots, it is instructive to look at current issues with root balls. Only then will you understand the possible benefits of washing roots.

Girdled Tree Roots

Most trees start out as liners. These are small seedlings, grown in very small pots. Liners  are then sold to other nurseries, who usually put them into a larger pots or into the ground and grow them for several years until they get bigger. Plants in pots are moved into larger pots as they grow. During this time they move from wholesale nurseries to retail nurseries.

If the process is done correctly, the root ball will never get root bound but in today’s busy world it is much more likely that the roots become root bound and start circling the inside of the pot. It costs nurseries too much time and money to fix the problem, so they just stick them into a bigger pot, hoping things will work out.

It is quite possible that the tree you buy does not look root bound, but inside of the root structure there exists an old root bound clump of circulating roots. If you follow the standard planting technique you will never know that you have a problem.

Is it a problem? Not while the tree is small, but as it grows it can become a big problem. As the roots expand in size they can strangle the trunk which usually leads to the death of the tree.

The picture above shows a tree that was root bound when it was planted. It died a couple of years later with this root system. The roots continued to grow in a circular pattern and never really entered the native soil nor did it develop a proper root system. This was OK for a short while, but as the top of the tree got larger, the roots couldn’t keep up and the tree dies. This type of problem can be corrected at planting time if the roots are washed so that you can see the problem.

For a more detailed look at the problems created by girdling roots have a look at this reference.

Root Ball Planted Too Deep

Each time the tree is moved from a small pot to a larger pot, it is important that the tree is planted at the right height. That takes extra time and money and many nurseries just don’t bother getting it right. They need a high level of productivity so they just plop the small root ball into a bigger pot, and fill it with soil.

This is not a serious problem if it is corrected at planting time, but the most common advice given to gardeners is to plant the tree at the same height as it was in the pot. If you do this, there is a chance the tree will die in future years due to girdling roots.

Keeping Soil On The Root Ball

Almost all the advice you read, or get from friends or the nursery will advise you not to disturb the soil around the roots. This makes perfect sense. As soon as you disturb the soil around the roots you will also damage the roots. The fine root hairs break very easily – you can’t help but damage the roots.

The problem with this advice is that usually the media in the pot is very different from your soil and unless it was a B&B (balled and burlapped) tree, the media in the pot is not even soil. It will be peat moss, coir or composted wood products. Even in the case of B&B trees the soil can be very different than your own.

The difference in soils results in watering issues and poor growth of roots into your new garden soil.

The Washing Technique

The claimed solution to all of the above problems is to wash all or most of the soil off the roots so that you can see existing problems. If there is a problem, fix it before planting the tree. Everything else about planting a tree is the same as described in my last post, Planting Trees the Right Way.

Remove the tree from the pot or burlap wrapping. Place it in a tub or wheelbarrow that is big enough to accommodate the whole root ball. Take a hose, turn it on high and start spraying the root ball. Knock off all of the potting material. As the wheelbarrow fills with water, try gently shaking the tree in the water. Use your fingers to remove potting material. You want to remove all or most of the soil from around the roots.

This process can take several minutes for root bound plants – take the time needed to do the job correctly.

Correcting Root Problems

With all of the soil removed, you can now clearly see what the roots are doing. You can also see the root flare where the upper large roots leave the trunk. The root flare determines the new planting height.

If the tree was planted too deep for too long, you might also see adventitious roots growing above the flair. These can be removed.

If you see circulating roots, you can cut them so that they are no longer circulating. This will seem drastic but it is important. Having fewer straight roots is better than having a lot of circulating roots.

Washing Roots – Does Science Agree?

One of the great things about science is that the so-called ‘accepted’ information is subject to change. This is especially true of new discoveries.

Washing roots on trees is new science. Some scientists say this is the best way to handle trees while others disagree. So far there is very little science to support the washing technique. One often referenced study looked at two types of trees, in one location. One of these was a weedy-type tree that grows easily – not really a very convincing study. This study also took place in the Northwest US, where temperatures are relatively mild and there is good rain fall. Similar studies have not been done in drier or colder climates.

The Garden Professors have talked about root washing for some time and they don’t agree on this topic. Two of the three, Jeff Gillman and Bert Cregg, both of whom do regular tree research,  do not recommend root washing. For more on this see their blog post about washing tree roots.

Washing Roots – My Experience

I have been washing roots on trees for a couple of years now. On some trees washing did not make much difference. The trees had been grown properly and were not root bound – there was no problem to fix. In other cases I found one or more problems and washing roots allowed me to fix the problems. The problem is that not all trees survive the process and I have seen an increase in tree deaths since I started using the process. This is especially true of deciduous conifers.

One of my pine trees that had been in the ground for about 5 years died this spring. This was planted using the old technique where I just removed the plant from the pot and placed it into the ground – soil and all. This was before I started washing roots. When I removed the tree, the roots looked just like the above picture – roots going around in circles. In 5 years very few roots had left the original hole in which it was planted. The tree simply out grew the poor root system and may have done better with root washing.

Should You Try Root Washing?

If you are a new gardener, stay away from this technique.

I would not recommend this as a standard way to plant things, but if you suspect a serious root problem, it might be worth considering as an option.

Always, remove the soil above the root flare. Everyone agrees that trees should be planted with the root flare just at the soil level. The only way to do this is to see the root flare.

If the soil in the pot is very different from your own, consider a partial removal of the soil. This is especially important if the plant is root bound. Removing about half the soil, and leaving the inner root ball intact, is midway between washing and not washing. You expose some roots to the new soil, but you limit damage to the root ball.

There is one additional piece of advice. Since the process of washing roots does damage the roots, it becomes even more important to water the tree well for the first year. It is also very important to keep it mulched which keeps the roots cool and prevents loss of water from the soil.

Tree Death by Strangulation

Ever wonder why you should remove burlap, string and wire baskets?

Best Time to Plant Trees

This is discussed in the post, Best Time to Plant Trees