Washing Soil Off Tree Roots Before Planting

By Len Phillips

Researchers are refining a technique to plant trees a better way.  It is simply washing the soil off the roots of a tree before planting it.  It does not matter if the tree is B&B, in a fabric bag or in a container, the tree ends up be planted as a bare root tree.

There are several advantages to root washing.  It exposes the root system so any kinked, circling, or damaged roots that might shorten the tree lifespan, can removed.  Root washing also makes the flare more easy to locate and makes the tree easier to handle and plant at the proper depth.   One factor often overlooked is greater root/soil interface.  The roots no longer have to pass from the soil in the root ball to a different soil in the planting hole.  While this may not be a major factor, it does decrease the time necessary for the tree to become established in its new location. 

The major disadvantage of this process is the time it takes to do the washing.  However this is offset somewhat by the ease of planting a lighter weight tree.  Experience with this process will also decrease the time necessary

Procedure

There are several options available to wash the soil off the roots.  The most popular is to remove the wire baskets and burlap or the container and place the tree in a pail, tub, wheel barrow or other water tight container and add water until the entire root ball is covered with water.  A wheel barrow or plastic drum works well for this step so excess water can easily be dumped into smaller buckets for reuse as water for the newly planted tree.  Soak the roots overnight or longer in water to loosen the nursery soil.  Remove all the soil with a gentle spray from a garden hose.  Also use your hands to release any clumps of soil that cling to the roots. 

Another method is to 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 or a three-pronged garden trowel to remove potting material and clay.  The muddy water that you save, is full of micro-organisms that were assisting the tree's growth before it was dug and will speed the transplant shock recovery time after planting.

After washing by either method, prune any damaged, broken or blackened roots back to healthy-looking tissue.  If circling roots can not be straightened they should be cut back to where they started to circle the container.  Shorten long roots to make it easier to plant, which will also increase the number of water absorbing root tips soon after planting.

Leave the roots in the water buckets until the minute they are ready to planted, but no longer than 24 hours.

The tree is now ready to plant using the procedures for bare root tree planting.

Planting the Trees

To plant, dig a hole that is shallow and tapered.  Make it deep enough to accommodate the height of the root system and two to three times the width of the extended root mass. This gives the roots plenty of room to quickly grow outwards in lightly-compacted soil.

Spread the roots out in all directions, radiating from the tree.  Make sure the flare is at or above the finished grade.  It is better to be too high than too low.

Use a spade to break up any compacted lumps of soil and loosen the soil on the sides of the planting pit.  Set the tree in the pit and orient it to the preferred direction.  Fill the hole with the same soil that was removed from the planting pit.  Do not use any type of soil amendment.  When half the roots are covered with soil, add the muddy water that was used to wash the roots and allow it to drain.  Then, finish adding the soil over the remaining roots to the final grade and add the remaining muddy water.  If possible all the water used to plant the tree should should be the same water that the tree was soaking in because it will contain the nutrients and microbes from the nursery soil.  If the soil needs to be firmed around the roots, use hands instead of feet to avoid any soil compaction.

Finally add a small berm of soil around the outside edge of the planting pit and cover all the newly added soil with a 3 – 4 inch layer of mulch.

By the time the roots have grown to the soil that was not touched during the planting process, the tree will be considered established.  With this root washing process, the establishment time is usually before the end of the first season.  Conventional planting of B&B or containers will require an average of 2 seasons to become established, depending on the tree size.

Staking a bare root tree is usually not required, but if the tree needs additional support, it should be done by using a root stabilization device and not the conventional stakes with ties to the upper trunk.

Since the process of washing roots does damage the fine roots, it becomes very 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 the loss of water evaporating from the soil.

The amount of water to be applied should follow this chart:

• daily watering for the first one to two weeks, applying approximately 1.5 gallons per caliper inch (1.5 liters per caliper centimeter) per watering,
• after two weeks, water the trees every two to three days for the next two or three months, with approximately 1.5 gallons per caliper inch (1.5 liters per caliper cm)
• after 2-3 months, weekly watering is necessary for the remainder of the season or until the tree is established.
• after the first year, if watering is necessary, it should be 1 gallon of water per inch of caliper.  This equates to 1 inch of rainfall per week.

Results

According to researchers, the greatest success with this method is archived by planting smaller trees.  Their survival rate, time to become established, and growth rate are best with a tree grown in the 15 gallon container.

Researchers wanted to find out if root washing had any negative impacts on the tree's future growth.  So they washed the roots of one-quarter of the 3-1/2- to 4-inch-caliper red maple trees.  One-quarter of the remaining trees were planted with the rootball intact, one-quarter had the soil removed by air blasting, and one-quarter were dropped 10 feet (to simulate removal from a truck), which caused some of the soil to fall off the roots.  Researchers planted a group of these trees in March and another group in July in the 95-degree heat.  By October, to their surprise, all the trees, regardless of the treatment, were deemed healthy and had similar growth rates.

Sources

• Flott, Jim, “Planting Trees The Root Washing Method”, Community Forestry Consultants, 2008.
• Harris, J. Roger and Nina L. Bassuk, “Tree Planting Fundamentals”, Journal of Arboriculture, 19(2), March 1993.
• Pavlis, Robert, “Washing Roots Before Planting Trees”, Garden Fundamentals, July 25, 2016.