Last week, we discussed some of the issues and barriers the roots of nursery-grown shrubs and trees face in establishing themselves. The most important concern is setting up improperly growing roots for success. Now let us look at a “new”, somewhat controversial, step to try when planting B&B (balled and burlapped), and most especially container-grown plants: root washing.

I was taught, in horticulture classes and by experienced landscapers, to dig the hole a bit wider and only as deep as the root flare. Then, we just set the tree in the hole and backfilled, stomping the soil down as we filled to stabilize the tree. I was taught to plant young trees whenever possible, as they establish more easily and can catch up to a larger tree in no time. Usually, we were planting a lot of material, so in the interest of time, removing any burlap and wire was skipped. I will say, I have planted many trees this way with success, but the idea that one should not disturb the roots is just not supported by the scientific literature. I have found working with the roots to be the most important step in planting, especially for the home gardener who is only planting a few things and has the time to work with the roots. This extra step can pay off!

Step 1- Preparing for Planting

As previously discussed, there can be a number of issues if one does not open up the root ball a bit. Roots are growing in various directions, and in the case of container stock, growing in what appear to be never-ending circles. The root flare tends to be buried, and secondary roots can start to grow above the flare, becoming girdling roots (which choke off the supply of water and nutrients) over time. What you think (and use to establish planting depth) is the top of the root ball, is actually several inches too high, and then you will have just planted a tree too deep, which can lead to a slow death.

To prevent this situation from occurring, you should, at the very least, open the burlap and scrape back the soil to find the flare before deciding how deep to dig the hole. This is where root washing comes in. Completely remove the basket and burlap, and then wash off virtually all the soil, exposing the main root structure. Next, prune out any large crossing or girdling roots.

Step 2 – Digging Your Hole

Once the root ball is exposed, you can see exactly how wide and deep you must dig the hole. Dig your hole up to twice the diameter of the root ball and only as deep. The common wisdom is to plant about a half inch higher than grade to take settling into account. This is especially important in heavier soils where the tree can be planted in a “bathtub”, where the heavy soil compacts and the water sits and doesn’t drain properly. Plant higher and the roots have some breathing room.

Step 3 – Checking Your Depth

Once I think my hole is deep enough, I place one shovel flat on the ground with grade and another upright in the hole. This helps me see if I achieved the proper planting depth.

Step 4- Setting the Plant and Backfilling the Hole
I encourage people to amend the soil very little beyond adding compost. If your tree is being viewed primarily from one side, decide which side looks the best before backfilling begins. Next, start placing soil back around the root ball. I use the handle end of the shovel to pack the first bit of soil down tight around the now exposed roots to help create a stable base and create good root-to-soil contact. When the hole is about half filled, water the soil in well. The percolating water helps to remove air pockets as well as get water to saturate the entire root zone. Water slowly to allow the water to absorb and keep it from running off. Keep backfilling until the hole is filled in completely.

Step 5- Mulching and Aftercare

After backfilling is complete, spread a nice three to four inch layer of mulch around the tree; preferably equal to the diameter of the tree’s drip line. Then, water once more. I like to water after I mulch as the mulch slows down the water’s absorption, allowing it time to slowly trickle into the soil.

A new tree should receive 1-1.5 inches of water per week and be fertilized with a slower release organic fertilizer. People often ask about, and I see way too much of, tree staking; usually, there is little need for it.

The most important thing when planting any nursery stock, whether it is a small annual or a large shade tree, is to get roots growing outward into native soil as soon as possible. I instruct all our volunteers as they plant to rip, cut or hack the root ball open, flaring the roots outward. Sometimes this means chopping the dense root mass with a shovel or pruners to break up the roots enough to pull them out. It is also a good idea to roughen up the sides of the containerized roots to pull more roots out of their “shell.”

 

No matter the planting method, the most important thing is to set the roots up for success. Do this, and your plant will reward you for many years to come.

Josh Steffen
Horticulture Manager