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How to Grow a Tree
by Arthur Lee Jacobson and Nota Lucas
Trees are appealing for many reasons:
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Aesthetics — we like the way they look, and they can block less lovely views.
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Practical — they can cool us and our homes and cars on hot days.
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Useful and important — they help clean air, reduce soil erosion, and provide food for us and for wildlife.
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Emotional — they make us feel good. Ever notice the way a neighborhood with mature trees feels compared to one without?
But while we like them, growing healthy trees can be challenging. What can go wrong? Plenty.
There are three basic principles to follow in growing trees:
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Plant the right tree in the right place.
- Plant it correctly.
- Provide the aftercare—watering, mulching, and pruning—it needs.
Plant the Right Tree in the Right Place
Choosing a tree is like trying to choose a product among competing brands: it’s not simple. Unless you gamble on an impulse, you either need to do some research yourself or get help from an expert. Here are some factors to consider.
Physical considerations:
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Available room for branches to grow
- Available room for roots to grow (buried tanks, cables, conduits, septic fields, hard pan layer, etc.)
- Soil characteristics (texture, drainage)
- Moisture availability in summer (Is the site arid or naturally moist? What are your plans for providing water to that portion of your yard?)
- Sunlight level
- Exposure to wind, heat, freezing, etc.
Aesthetic considerations:
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Desired mature size (think at least 20 years down the road!)
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Evergreen or deciduous
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Leaf and trunk color and shape
- Flower visibility and timing
- Leaf drop habits
- Disease and pest tolerance
Regulatory considerations, if any:
- Covenants
- Environmental regulations
- Building and sidewalk codes
- Permits needed
Once you’ve done this basic legwork, it's time to think about planting and caring for the tree you select.
Ideal planting, mulching and aftercare
Fall planting is best
Nurseries have the best selection of trees in spring and early summer. But even if you water with care, you risk losing your plant to drought stress if you plant during the dry season, since the roots have not yet become established. And the thirstier the species of tree, the dicier planting in summer can be.
Many trees we like to grow here, such as the Katsura tree, come from parts of the world with ample summer rain. The Katsura is native to Japan, which gets well over 20 inches of rainfall between May and late August—compared to only 5 inches of rain in Seattle! So keeping a new tree watered during our dry summers is an uphill battle.
Taking advantage of fall rains is one great reason why it is best to plant in fall. Yet many fear that nursery stock will be picked over by then, or that the remaining trees will be root-bound or will have been watered erratically. The good news is that some nurseries are beginning to bring new fall stock in as the wisdom of fall planting is becoming more widely appreciated! Do consult with nursery staff to make sure you get a good tree.
With these caveats in mind, you may choose to purchase your tree whenever you find a good specimen; remember to plant and water with care. All new plants—whether drought-tolerant or thirsty—need regular water until their roots become established.
Don’t plant with congested roots
Healthy roots bring the best growth. Plants whose roots are too tangled or twisted for optimal growth may be stunted for life, and they are more likely to blow over. Consult a good reference book or website if you are not experienced with tree planting, and pay special care to the roots.
Don’t plant too deeply
Plant on a slight mound and your little tree will settle properly. If you plant “level with the nursery line,” it may settle too deeply. If needed, bring nearby soil to make a mound.
Don’t amend the soil!
The old advice about amending the soil in the planting hole is just plain wrong. The roots will never want to leave their nice fluffy home. Loosen the soil when digging the hole, but your best bet is to select a tree suited to your soil type. Water the soil carefully in the planting hole and firm carefully to make sure you get good contact between the soil and roots. (However, if you are redoing a large garden area, do amend your soil with compost!)
Mulch properly
Absolutely DO use organic matter on top of the soil once you have planted and watered your new tree. This mulch layer will suppress weed seeds, conserve soil moisture, and improve soil as the organic matter in the mulch decays. Though there are differences in mulch products (see Resources below)—you can choose wood chips, ground bark, sawdust, old leaves, compost —using mulch is more important than what you mulch with. Consider using what is most readily available.
Water your tree
Proper watering does require some thought and effort, but it is essential to establish a healthy tree. All plants require water at least until their roots become established and can take in water from surrounding soil.
You can water new trees using a green watering bag (available at local nurseries or online), soaker hoses or drip lines, or a watering wand . However you water, remember that you want to moisten the root zone of the tree, which may be deeper than that of surrounding plants. Then let the soil dry out some before you water again. Frequent, light watering can result in shallow, less healthy roots for any plant—and can be particularly stressful for trees. The idea is to give roots the water they need and encourage them to grow deeply, not to stay near the soil surface. After a summer or two, the tree should be able to fend for itself if it was selected, planted, and cared for thoughtfully.
Keep in mind that too much water can be as much of a problem as too little. Besides wasting water, overwatering can hurt trees by encouraging fungal growth and reducing the amount of oxygen available to the roots. For many species, such as aspens, less water also induces brighter fall color.
This watering issue is exactly why we should plant more trees that need little or no watering once established. Don’t exclude thirsty trees, but use them sparingly and plant them where ground water is available, for example, near streams.
Prune thoughtfully
People have different ideas of how a tree should look, but proper pruning can make the difference between a great tree and a disaster. Pruning can thin trees, such as purple-leaf plums, to make them more elegant in form. And it is essential for fruit trees, making them easier to harvest, more productive, and easier to climb! Other reasons for pruning include limiting plant size, preserving views, managing sunlight, or keeping branches clear from wires, buildings or paths.
Pruning is such a major topic that entire books guide the practice. See Resources below for more information about pruning and related matters.
Resources
Plant Amnesty (local nonprofit group teaching pruning, providing free referral service, and more)
City of Seattle ReLeaf
WSU Gardening Website
Urban Forestry Index
Elizabeth C. Miller Horticulture Library
More mulch information: Summer Savvy Gardener article
Arthur Lee Jacobson, Seattle’s ‘tree guy’, is a lifelong Seattle resident and professional plant expert, and is passionate and knowledgeable about both wild and cultivated greenery. You can visit his website at http://arthurleej.com.
Arthur Lee Jacobson’s ideal less thirsty tree choices (pdf)
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