Don't let these common tree-care myths prevent you from taking proper care of your landscape trees.
In the 1800s, many American citizens became alarmed by the rapid deforestation occurring across the country. Determined and public-spirited people gathered and assisted one another with foresting and reforesting scantily wooded areas and small towns. In 1872, this movement was taken a step further when Julius S. Morton of Nebraska succeeded in convincing his state to set apart one day, April 10, to systematically plant as many trees as possible. When legislature eventually declared this day a national holiday, they decided to hold it on April 22, Morton's Birthday. In honor of Arbor Day, we have asked garden writer Patricia Fletcher and horticulturist Dr. Richard Harris to dispel the top-10 myths regarding proper tree care. And come April 22, we encourage you to plant a tree or two yourself … or at least hug one.
Myth: A tree that looks lush and full at the nursery will grow and flourish in the landscape.
We often equate good looks with good health. But to choose a tree based solely on appearance is to ignore a possible life-threatening condition of container-grown or balled-and-burlapped plants. Because of the confinement of containers, trees sold at nurseries sometimes have dangerous circling root systems that may literally strangle the plant in later years. Always check the top of the root ball for girdling or kinked roots and straighten them out when planting.
Myth: The planting hole should be twice the depth of the root ball.
Gardeners tend to have deep thoughts about planting. It's an all-too-common practice to dig a planting hole bigger than necessary. However, unless the soil is compacted, the planting hole should be dug as deep-if not less so-than the soil level in the container.
The root ball should be planted high and proud, with its top at least an inch above the surrounding finished grade in all but sandy soils. This is because-after planting and watering-the root ball may settle in the planting hole and then become covered with soil, which creates a barrier to water penetration. "I've seen cases where the soil on top and around the root ball is muddy and the root ball is dusty dry:' says Harris.
Myth: Backfill soils (those used for refilling the planting hole) should be amended with organic matter.
When it comes to supplementing backfill soils, less is more--more or less. There has been no consistent evidence to show that amending the backfill soil with organic matter, such as humus mulch, is beneficial. In fact, some studies indicate that roots won't grow through amended soil into surrounding soil. In most situations, the soil that is removed from the planting pit is fine for backfilling around the roots of the tree.
Myth: You can improve drainage by placing a layer of gravel at the bottom of a planting hole.
Sheer physics defies this one. When you place a dry sponge under a faucet, notice how it will absorb water only up to a "point of saturation:' as the scientists say, before it releases water into the sink.
Water movement or drainage in landscape soil is similar. A layer of gravel underneath the root ball will act like the surface of the sink in the example of the sponge, preventing water from continuing to drain downward. This causes the soil and root ball to become saturated-like the sponge--before water can drain through the gravel layer to the soil below. This excessively wet condition is detrimental to root growth, as it deprives the soil of vital oxygen. "Just putting gravel in the bottom of the hole with no place for the water to go makes drainage worse," warns Harris.
To intercept excess surface water before it reaches the planting hole, auger a column of sand draining down and away from the root ball, three to four feet deep and four inches in diameter.
Myth: All newly planted trees should be staked for support.
This lean-on-me philosophy causes a tree to grow tall too quickly, which doesn't allow time for proper development of the root system and trunk taper. (A tree's trunk should be larger in diameter at the bottom than at the top, creating a strong base.) Additionally, a rigidly staked tree with multiple ties has little opportunity to move and bend with the wind As a result, the tree will not develop the strength and structure it needs to stand once the stakes are removed "Unfortunately, we tend to buy our trees by height, seldom looking at the diameter of the trunk," says Harris. While trees that can stand on their own will require staking for support, try untying a new tree from its stake; if it stands, let it be.
Stakes are actually great for protecting a young tree's trunk from injury and for anchoring the root ball to the surrounding soil. A supporting stake, as low and short as possible, with a single flexible tie, will allow the top of the tree to move more freely. The tree's growth in height will slow, allowing lateral growth and development—the route to a tree's strong stance.
Myth: To grow well, all newly planted trees need pruning, which balances the top with the root system.
Pruning trees to balance the foliage with the roots eliminates leaf surface, growing points and hormones that not only supply nourishing carbohydrates but also stimulate root growth, according to Harris. Removing branches from the lower half of a young tree may give it a mature, formal look, but it prevents proper trunk taper and diameter necessary for structural integrity.
In young trees, the prime reason for pruning is to develop the branch structure. Branches that are bigger than the branch or trunk from which they arise should be removed, as should those that cross or are too close to the permanent scaffold or framework branches. But keep the branches below the lowest permanent scaffold branch for several years: Cut them to less than 12 inches in length during the dormant season, removing the largest ones first and pruning off the remaining branches over a two to three year period Also, leave lower branches on the south and west sides of the trunk to reduce the chance of sunburn.
Myth: Mature trees should be topped and headed back to control their growth.
The mark of a good pruning job is actually no mark at all. By using certain thinning methods, few people will recognize that the tree has been pruned, as opposed to the obvious hack job on a tree that's been topped and headed so much that it resembles a hat rack.
Any time you prune off live branches and leave stubs, there will be vigorous concentrated growth just below the cut. This type of pruning gives rise to branches that are close together, upright, and weakly attached. When using thinning methods, however, a branch is completely cut from the point where it arises. Thinning cultivates branches that are strongly attached, have a more graceful appearance, and allow more light into and under a tree.
Myth: Trees need a complete fertilizer.
A complete fertilizer contains nitrogen, phosphorus, and potassium. In most of California, for example, Mother Nature has provided plenty of phosphorus and potassium in the soil. According to Harris, studies have not shown improvement in tree growth from adding phosphorus or potassium to most oils. However, nitrogen is almost always deficient in soil and usually is the only fertilizer needed by trees.
Myth: Pruning cuts should be flush with the trunk.
"There's good evidence that if you flush-cut branches, you are cutting into trunk tissues," warns Harris. If decay should begin, it would have easy entry. The best way to prune branches is to make cuts just beyond the limbs' "branch bark ridge;' a bump or roughening of the bark on the trunk where the branch is attached.
Myth: Pruning cuts require pruning paint to deter decay.
With the right pruning cuts, as discussed above, pruning paint is unnecessary. Additionally, simply sealing a wound with paint or asphalt will not prevent decay; in fact, it could create ideal conditions for infection. "If it's a thick material such as the commonly used asphalt, it doesn't adhere tightly to the wound because the wound is moist after pruning;' says Harris. It may crack, allowing water to get under the paint from sprinklers or rain. This creates an ideal place for decay to begin.
Editor's Note: Patricia Fletcher is a gardening contributing editor and free-lance writer for Northern California Home & Garden.