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Caring for Container Trees and Shrubs
Plan to provide trees and shrubs planted in containers regular waterings and frequent feeding as special care they need to stay beautiful and healthy. Potting soil in containers dries out and fertilizer is used up more quickly than in regular garden soil.
Watering Container Plantings
Regular watering—frequency and quantity—is vital to healthy container trees and shrubs, even more so than for ground-plantings. Pots may overheat and lose water, water may pass through porous containers made of wood or terra cotta, and water frequently drains away through drainage holes.
How much and how often to watering your containers depends on many factors:
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- the size of the container in relation to the tree or shrub it contains,
- the amount of sun the plant receives, and
- the porosity of the container.
Your goal is to keep the soil evenly moist during the growing season, without letting it be either overly dry or too soggy. The best way to determine when to water is to press your finger 2–3 inches (50–75 mm) into the pot’s soil.
Feel the soil. If the soil is dry several inches deep, give your plant a good soaking. If it feels damp or wet, wait to water. You’ll probably notice that—especially during the dormant season or when rain is frequent—you’ll need to water less often, if at all.
For ease of care, install drip irrigation for your container trees and shrubs [See: Container Drip Irrigation]. Automatic timers make applications on a preset schedule or by using a moisture sensor to measure soil dampness. Still, they require occasional attention to make sure all is well with your plants in their pots.
Fertilizing Container Soil
One negative side effect of frequent irrigation of container plants is that soil nutrients—fertilizers that reside in potting soil as water-soluble salts and minerals—dissolve into the water and carried away. The process is called “leaching,” and it means you must replace the lost nutrients.
To keep your containerized tree or shrub healthy, supplement its soil with fertilizer on a regular basis. Choose to apply a water-soluble fertilizer, sprinkle granular fertilizers on the top soil in the container and mix it in, or apply a liquid foliar fertilizer directly to your plantings’ foliage [See: Fertilizing Trees and Shrubs].
Regardless of which type and method of fertilizing you choose, always read carefully and follow exactly all the fertilizer package’s directions regarding the mixing, amount to apply, and frequency of use.
Other Container Care
There are a few other care tasks you should do from time to time that will benefit your container trees and shrubs.
If your plant is stagnating, or if you are having to water more and more frequently to keep the shrub or tree healthy, its time to transplant it to a larger container or renew its soil medium.
When its time to upsize, choose a new pot with a diameter at least 4–6 inches (10–15 cm) wider than the current container. For best results, follow the instructions for carefully transplanting into the new container [See: Transplanting Shrubs].
Remove the rootball carefully by inverting the container and allowing it to fall into your hands; never pull on the stem or trunk of the plant.
Next, fan out the root system, unwinding any roots that grew in circles around the interior of the old pot, “girdling” and strangling the tree or shrub. Partially fill the new container with fresh potting soil, dampen it, and then place the tree or shrub inside. Finally, fill along the sides and compact the soil around the rootball.
Always water thoroughly after repotting, allowing water to run through the pot’s drain until it stops and all air pockets have been filled. Apply a finishing layer of mulch over the top of the soil.
Sometimes shrubs or trees in containers don’t require repotting, just minor refreshing.
It’s a good practice to gently remove the top inch (25 mm) of soil from the container every other year and replace it with fresh potting mix.
Every 4–5 years, your tree or shrub should receive remedial root pruning.
Remove it from its container as described, and cut back the tips of all its visible roots to force new growth. Cut out most of the larger, woody roots before repotting, leaving three or four to regenerate new hair roots.
Strip leaves until those that remain are roughly equal in volume to the remaining roots. Reducing foliage helps the tree or shrub adjust, triggers new growth, and quickly recover.
Generally, you can return the plant to the same container after root pruning. You should begin to see new foliage sprouting in 3–4 weeks. Following this procedure will keep your container trees and shrubs healthy and beautiful for many years.
Container Plantings Care
Key steps in the care of container plants: mounting the pot on a raised, rolling platform; applying fertilizer; staking; care during frost; and moving the plant inside during prolonged times of cold or in winter.