Ask me what's the best way to plant a tree or shrub.
Unlike the advertisements that start off with "experts agree that ..." or "nine out of 10 dentists recommend," it's unlikely that you'll find another horticultural expert that will agree with me 100 percent.
If you consult references or websites, you'll find that they each have a slightly different slant too.
Why so much disagreement? It's because horticulture is not an exact science. Plants behave differently from location to location based on many different factors ... how they're propagated, where and how they're planted, soil conditions, climatic factors and the care given after planting. All around the country, too many trees and shrubs in landscapes fail to thrive due to the way they were planted. Because so many factors are involved, horticulturists have developed different approaches to solving common planting problems.
One very common problem is with "B&B" or balled-and-burlapped plants, ones that are dug out of the ground and then the roots and soil are wrapped in burlap and secured with twine. It used to be a common practice to only loosen the twine and leave the burlap around the root ball when a tree or shrub was planted. It was thought that the burlap and twine would rot quickly and not impede root growth.
Today, much of the burlap that's used to encase plant root balls is treated with copper to keep it from rotting in the nursery. The copper treatment gives the burlap a green tint. Unfortunately, the copper also slows the rot of the burlap in the ground. In addition, copper is toxic to plant tissues. Roots will fail to grow when in contact with the copper left behind when the burlap eventually rots. Even if not treated with copper, buried burlap doesn't seem to rot very quickly in our region.
I recommend situating your tree or shrub correctly in the planting hole, then cutting off and removing all the burlap and twine around the ball. Others recommend folding it back and leaving it in the bottom of the hole, but this interferes with water movement. Some recommend slashing or cutting up the burlap but not removing it. This also interferes with water movement, and treated burlap will still retard root growth.
Without removing burlap, you have no way of examining the base of the trunk and root ball for defects. You can't determine the location of the root collar. The root collar is where the trunk of a tree flares outward and the root system begins. When nurseries dig and prepare balled-and-burlapped plants for sale, soil often becomes mounded around the trunk and the top of the "root ball" ends up being far above the root collar. More about this in a moment.
Many tree and shrub plantings fail because they end up with root systems situated too deep in the soil. The majority of experts recommend planting trees and shrubs with the root collar at grade (soil level) or 1 to 2 inches above grade.
If soil is mounded up around the trunk of a plant, you can't determine the location of the root collar. That's yet another reason to remove the burlap from B&B plants, but bare root plants and container grown plants often end up planted too deep too.
For years, most of us have dug deep and fairly narrow holes to accommodate root balls because we envisioned trees and shrubs with deep tap roots. However, trees and shrubs planted in home landscapes, parks, and along streets don't usually have tap roots. Instead, the root systems they develop are wide and fairly shallow. Planting holes should only be as deep as the root mass and three to five times the width of the root ball. When plants are placed in deep holes, they have a tendency to settle after planting and soon end up planted too deep. That's why most experts now agree that planting holes should be wide and only deep enough to accommodate the root ball.
Once the tree is situated in the hole at grade or slightly above, it's backfilled with the existing native soil, minus any large rocks, extraneous roots or debris. The soil should not be amended with any type of organic matter. Then, the plant should be thoroughly watered in. Stick a hose right into the hole and let the water run. This helps eliminate air pockets around the roots.
Once the hole starts overflowing, let the water drain and see if you need to add more soil. Gently firm the soil around the roots with your hands. Absolutely do NOT compact the soil by stomping on the roots and soil.
Finally, mulch the entire planting area with at least a 4-inch layer of aged wood chips or shredded bark. Keep the mulch at least 6 inches away from the trunk of the tree.
* Marianne C. Ophardt is a horticulturist for the Washington State University Extension Office in Benton County.