Root Washing: What it is and Why You Need to do it When Planting Perennials

Years ago, common advice when planting trees and shrubs was to ease the plant out of its nursery container and drop it in a 2X wide hole with the planting medium intact. Then backfill with compost and soil and off you go. It was thought that not disturbing the roots would allow them to expand vigorously into the neighboring soil.

Unfortunately, recent research (and even my gardening experience) has shown that this planting technique can result in shrubs and trees that may not thrive, and it may even lead to their demise. More than a few times, I’ve removed plants from my garden and others whose roots did not expand outside of the planting hole even years later. This is especially true for trees whose burlap wrap was left in place. Restricting root development like this not only starves the plant of nutrition but results in poor anchoring, leaving the shrub or tree vulnerable to wind and weather.

What is root washing?

Root washing is the removal of all of the planting media from a tree or shrub’s root ball before planting it, followed by pruning out dead or damaged roots. To ensure success, gardeners should also observe up-to-date planting techniques. This gives your perennials the best opportunity to thrive in your garden. Establishing a healthy root system creates a healthier plant overall, requiring less fertilizer and fewer pesticides.

Removing the potting media allows the plant to pour its stored resources into spreading its roots into neighboring soil. This quickly anchors the plant and creates an opportunity for it to gather nutrients from the surrounding landscape. While top growth may initially appear slow, rest assured that plenty of work is going on below ground.

When a plant is planted with its root ball intact, the plant will initially form new leaves and flowers. That’s because the roots have not been disturbed, and the resources stored in the plant are poured into top growth and reproduction. But when resources are spent on top growth, fewer are available for root growth, which diminishes the health of the plant below the soil line. And eventually above. The result is a plant that may not thrive and eventually dies. It may take years to happen, but it’s inevitable.

Why do plants become rootbound in containers?

Plant roots prefer to grow evenly outward and around the trunk of a tree or shrub rather than down into the ground. This is apparent if you’ve ever planted a perennial seedling in open soil – the root system will grow outward like spokes on a wheel. When plants are not potted up correctly by growers, the roots grow to the side of the container, where they hit the wall and then begin to circle, searching for open soil. Not finding any, they continue to circle or grow vertically. If this occurs for too long, the roots grow over each other, causing the root ball to become root-bound.

As the plant’s roots age, they become woody and rigid. This leaves them fixed in the circling position. Without correction, they’ll continue to circle, even after being planted. Eventually, the plant becomes “girdled” – the roots wrap so tightly around themselves that they effectively choke the plant off from its resources. Rootbound and girdled root systems are less likely to establish and won’t thrive in your garden. Most girdled plants will die prematurely. Research has shown that once plant roots start growing in a circular pattern, they do not typically change their growth when planted unless corrected by the gardener. This is why root washing and correcting root problems at the time of planting are best practices.

How to wash plant roots

Washing the roots of shrubs and trees (perennials) helps them transition quickly to your garden and identifies any root system problems. Ideally, root washing should be done when the plant is dormant, just as with planting or transplanting. Root washing or planting during the growing season adds stress on the plant but can be successful if care is taken to follow best practices. Note that this advice applies to plants in containers or transplants.

1. Work in a shaded area to minimize stress on the plant. You’ll need access to water, preferably from a garden hose. Once you begin, the roots must be constantly wet.
2. Remove the plant from the container and remove any wires, string, or burlap. Gently shake off as much planting media as possible.
3. Place the plant in a large bucket, wheelbarrow, or a similar container and cover the root ball with water to soak. This may take 15 minutes or up to a few hours, depending on how dense the root ball is. Do not allow the root ball to dry out at any time. The idea is to saturate the planting media stuck to the roots so it can be easily removed. This also hydrates the root system before planting.
4. Remove the plant from the container and direct a gentle stream of water with the garden hose on the root ball. Use your fingers to gently loosen the roots and planting media. If it’s tough going, place the root ball back into the container to soak some more. Keep working at the root ball with your bucket, garden hose and fingers until the media is removed.
5. Once you can see the roots, identify any problems. Are they winding around each other? Are they overly woody? A perfect root structure spreads out like spokes on a wheel. Gently ease the root system as close to this formation as possible. Prune out thick, woody roots. Intertwined roots should be teased out if possible. Fibrous, fine roots should be kept intact and spread out by hand in your planting hole. Often, roots grow along the trunk of a tree or shrub that has been planted too deeply in its container. Remove them down to where the root flare transitions into the uppermost roots.

Correct planting is key to the plant’s health

• Dig a hole twice as wide but only as deep as the root ball.
• The proper depth for the plant is with the root flare just above the soil line (this is where the trunk meets the roots)
• Spread the roots as wide as possible in the hole.
• Backfill with native soil, not compost or treated soil. Do not press down on the soil with your hands or feet.
• Once the hole is filled, soak liberally with water. If you see air pockets develop, or if the soil sinks, top it off with more native soil.
• Cover the surface with wood chip mulch to insulate the soil. The mulch should be 2-4 inches deep.
• Give the plant a wiggle once a week. As the roots establish and grow into the surrounding soil, it will have less “give.”
• Fertilization is not necessary for perennials at planting time.

An easy rule of thumb to see if your plant is at the correct planting depth:

Proper planting depth with the root flare above the soil line is key to a shrub or tree’s long-term health.

• Place the plant in the hole.
• Lay a yardstick or something else narrow and flat across the hole. The yardstick should cross the plant at the root flare, where the soil line should have been in the container. Frequently, plants are buried below this point in their containers.

Source: Fine Gardening and Clemson Cooperative Extension