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Master Gardeners: Time to Prune Ornamental Trees

Ornamental Trees – Planting, Staking and Pruning

This is the ideal time of year to plant bare root or potted ornamental trees. When choosing new trees for your landscape consider: purpose of the tree (shade, focal point, fall color, etc.), soil type, sun and wind exposure, and water demands.

Once you decide on the tree, it´s time to go to the nursery and find the best specimen of that species. Look for a tree whose trunk is tapered, as opposed to pencil straight. The trunk diameter should be larger at the base than at the top. And choose a small tree (five-gallon size); it will have a better root to shoot ratio—the tree must have a developed root system before the top can grow.

Planting: Don´t amend the soil in the planting hole with compost, peat moss, or leaf mold, because the roots will never leave the planting hole site. Dig a hole three to fives times the diameter of the tree´s root ball, leave a pedestal of soil in the middle of the hole for the root ball to sit on, and keep the root ball 1-1/2 to 2 inches above grade. Score the sides of the hole to give the roots something to “grab onto” and “rough up” the root ball.

Speaking of roots, how do they grow? I was astounded to learn that 99% of tree roots are within the top three feet of soil! 85-90% of the absorbing roots are in the top 18 inches of soil, with the top 6 inches containing the majority of those.

Place two fertilizer tablets on either side of the root ball. Fill in the hole with the original soil you removed. Cover the top of the newly exposed soil with compost or mulch. Since the first nine weeks are critical for root growth, the tree should be watered every 2-3 days for two months, then once a week until the rains begin. Be careful not to over water—roots need air spaces in which to grow.

Staking: If your tree came with stakes, remove them after planting. If stakes are left on they will inhibit strong root growth. Staking is used only to protect, anchor and support the tree. By not staking you will achieve better caliper at the base, better tree taper, greater wind resistance, better root system, and less chance of mechanical injury.

If the tree is leaning over 45 degrees or more, or will be growing in a windy area, staking may be appropriate. Use two stakes—one on either side of the tree—at least 6-8 inches from the trunk and lower than the top of the tree. Place ties at the lowest point on the trunk where the tree will remain upright. Nylon hosiery makes good ties—it´s soft and flexible and lasts until removed. By staking in this fashion, the tree can move in the wind which causes excellent root growth. Stakes should not be left on longer than a year.

Pruning: Pruning corrects growth faults and improves tree structure. It should be started when the tree is first planted and continued at regular intervals when the tree is young. This results in removing the smallest possible amount of living tissue at any one pruning. However, regardless of age, you should always remove dead, broken, split, dying, diseased or touching branches.

You should also know if your tree should have a central trunk (Flowering Dogwood or Catalpa) or if the species is multi-trunked (California Buckeye or Chinese Elm). Never top a tree as it not only ruins the beauty of the tree, but also promotes the growth of many small branches that are structurally weaker and tend to break.

Through pruning you can promote the proper structure of the tree by thinning branches, training to a single leader, removing laterals competing with the leader, giving adequate branch spacing, avoiding narrow branch attachments and keeping laterals smaller than the trunk or branch.

Contact the Master Gardener Office at 533-5696 if you have questions. See you in the garden.

Master Gardener Carolee James is looking forward to spring gardening, which translates to pulling weeds, planting annuals, pulling weeds, planting a rose garden and pulling weeds (and pruning)!