June 22, 2018
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Planting field-grown trees in the garden

By Reeser Manley

There was a time when most trees were field grown, dug by hand from long rows, then balled and burlapped in the field before being trucked to the nursery yard for sale. Less than two decades ago, I stood in a Massachusetts field and watched a crew of four migrant workers dig and wrap a 6-inch caliper tree with a 60-inch soil ball in two hours. They were artisans, beautiful to watch.

They were also among the last practitioners of this skill. Everywhere else the task had been handed to one or two men and a tractor-powered tree spade. And then it became clear that a grower could not keep giving away a portion of his topsoil with every tree sold. Field-growing gave way to tree production on the top of the ground in plastic containers.

Most shrubs and small trees are now container grown, but larger trees are still dug from the field and sold balled and burlapped (B&B). In this process, less than 20 percent of the tree’s feeder roots are retained in the ball. In my opinion, buying B&B trees is a gamble with success measured in the time the gardener is willing to spend in planting and care during the first few years after planting.

Planting a B&B tree requires a planting hole wide enough for the gardener to remove the root ball wrappings AFTER the tree has been positioned in the hole. The hole should be 1- to 2-inches shallower than the height of the root ball.

Once the hole is dug, remove the wrapping added for convenience in marketing, such as shrink wrap or other container, but do NOT remove the burlap, wire basket, and twine that hold the rootball together until the tree is set in place.

Set the tree in the hole, making sure that the top of the rootball rises 1- to 2-inches above grade. This compensates for the extra topsoil added over the top of the ball during the digging and wrapping operations. If the rootball is too deep in the hole, remove the tree and correct the hole’s depth, firming any added soil at the bottom of the hole.

Make sure that the tree is standing straight, then firm a shallow ring of soil around the bottom of the ball to stabilize the tree. Now, remove all of the wrapping on the upper 12 inches or the upper two-thirds of the rootball, whichever is greater. Wrapping materials left under the rootball are not a concern since new roots will grow outward, not downward.

At this point, I like to use my hands or a digging fork to carefully remove soil from the edges of the rootball until I expose roots. This gives me a chance to inspect the outside of the ball for circling roots and either tease them outward with my fingers or cut them away with pruners. Removing the outer inch or two of soil also puts the roots in immediate contact with the backfill soil, eliminating potential problems with root growth at the rootball-backfill interface.

Should the backfill soil be amended with organic matter? (Remember, you have already significantly modified the soil in the entire wide bed area by digging or tilling.) Generally, the answer is no, unless the backfill is mostly clay or mostly sand, in which case amending it with no more than 25 percent (by volume) aged compost is recommended. The organic matter should be thoroughly mixed with the backfill, not added in layers.

Otherwise amending the backfill soil is fraught with problems. It may delay growth of new roots beyond the planting hole and even lead to root circling within the hole. The excess organic matter increases soil water-holding capacity which may lead to drowning roots. And, as the organic matter decomposes, the soil volume diminishes, allowing the tree to topple.

Now begin filling the hole with backfill soil. Add the backfill in increments and allow gentle watering to settle the soil around the rootball. Never walk or stomp on the backfill as this compacts the soil and shears roots.

When done, no backfill soil should cover the top of the rootball; backfill soil should cover the rootball “knees,” or edges, and taper gradually down to the original soil grade. This approach compensates for the added soil on the top of the ball and avoids planting the tree too deep.

As with container-grown trees, the final step is mulching the entire planting bed with three inches of aged compost. Avoid “volcano mulching,” piling mulch against the trunk, which traps moisture against the bark causing disease and decay. You should always be able to see a ring of bare soil around the base of the plant.

For instructions on creating the wide planting bed, see last week’s column at http://bangordailynews.com/author/reeser-manley.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

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