River Birch – Think Before You Plant

River-Birch-

River Birch – Think Before You Plant

Over the years, river birch trees have become a staple in almost every Augusta landscape—both commercial and residential. And that’s understandable as these lovely, multi-trunk trees with ruffled bark and texture add interest in the landscape and grow quickly into shade trees.

Unfortunately, they tend to outlive their welcome as gardeners tire of their summer shedding leaves, constant dropping of small limbs and shallow exposed roots. Even the once textural bark is no longer textured with age.

In addition to these high maintenance issues, river birch are also very difficult to maintain as healthy, long-lived specimens. If they aren’t planted in the right place and maintained properly, birch trees begin to decline within a few years and many of them die well before reaching maturity, which is generally 40 to 50 years.

The river birch is a native tree, which grows naturally in cool, moist soils of forests. They are also most often found at the edge of the woods where they get plenty of sun. Their shallow root system makes them sensitive to even short periods of drought or heating of the soil. Therefore, it is essential  to plant them in places where the soil is shaded, cool and moist. That may seem simple enough until you consider that river birch also require full to partial sun on their leaves to thrive. Finding a site in your yard where the soil will remain cool and moist, but the tree will also receive full sun on its leaves for much of the day, can prove quite a challenge.

The first place to consider as a planting site is the east and north sides of a your house or other structure, positioned where the building provides afternoon shade on the ground. Avoid southern and western exposures where the afternoon sun heats and dries the soil. Existing trees can also provide the necessary shading. A great time to evaluate your landscape for a proper site is mid- to late-afternoon.

Once you’ve identified an appropriate planting area for your tree, you still need to consider several other factors. River birch trees will grow 40 to 50 feet in height. So make sure you aren’t planting them where they will eventually become entangled in overhanging power lines. Also avoid planting in hard clay and soils that are compacted or likely to become compacted, such as along trails or driveways.

There are many varieties of birch trees, but the only one well-suited for our Southern climate is Betula Nigra Ornative river birch. Two varieties within that species, Heritage and Dura-Heat, are good choices. It is a waste of your time and money to plant other species of birch trees as they are almost certain to fail.

Cultivation

Mulching, watering, fertilizing and pruning play a critical role in the cultivation and maintenance of a healthy birch tree, with proper mulching and watering being the most important.

Aside from aesthetic benefits, mulching moderates soil temperatures (keeps soil cooler during the summer heat), conserves soil moisture, reduces competition from other plants such as weeds, adds organic matter to the soil as it decomposes and reduces soil compaction. The decomposition process also helps build new layers of soil with improved structure, which aids in better water retention and oxygen exchange. Placing mulch around the base of a tree reduces the likelihood of damaging the stem with a lawnmower or weed trimmer.

The best mulch materials are organic and non-matting such as pine straw, wood chips, shredded bark and leaf compost. Avoid stones or rocks as they can actually heat the soil and will not reduce weed growth or add organic matter to the soil. Do not place plastic under mulch since it can retard water movement and oxygen diffusion into the soil.

Sufficient water is probably the single most important factor in maintaining a healthy birch tree. If rainfall is insufficient, supplemental watering will be necessary. During the growing season, a slow (two to three hours), deep, (eight to 18 inches) watering once a week is a general rule for maintaining adequate soil moisture. Unfortunately, infrequent, light watering is a much more common practice—especially if the homeowner is relying solely on an automatic sprinkler system.  Laying the hose on the ground and allowing it to run slowly over the root zone is the best way to ensure the tree gets adequate water. Soil that can be formed into a ball in your hand has sufficient moisture; loose, dry soil that crumbles in your hand indicates the need for additional watering. Decrease watering by early to mid-October to allow for proper winterization of the tree.

Even when you are watering enough for the lawn, it is usually not enough for the tree. An under-watered tree will drop leaves once or twice during the summer since it doesn’t have enough water to support all the leaves on the tree. And many times, even when it does receive sufficient water, the tree will defoliate somewhat during periods of extreme heat so common in Augusta.

Fertilization is beneficial only when nutrients are lacking. A soil test will determine nutrient needs. If a tree is showing stress, don’t always assume it needs fertilizer. In most cases, applying fertilizer is the worst thing you can do if you don’t know the problem.
The best time to fertilize is in March and September. An additional application can be made during May. Nutrients should be available to the tree during its peak growth period in the spring and early summer. When a tree is located in the lawn area, it usually gets sufficient amounts when the grass is fertilized. Slow-release tree spikes are another option.

Pruning

As with other trees, river birch should be pruned early in their lives to develop a good structure. Prune out co-dominant branches. As the tree grows larger each year, you can prune a few of the lower branches. Never prune greater than 25 percent of the canopy of the tree. A large tree can be pruned most anytime—during the growing season or even winter. For trees five years or less, it is best to prune them after the leaves have come on the tree and have hardened off, usually in late April or May. Try to avoid pruning during late winter or early spring just prior to bud break as this causes the trees to bleed profusely.

Fortunately river birch trees are nearly pest free. The dusky birch sawfly caterpillar larvae are the main threat.  These larvae are yellowish in color with black dots down their back. They feed in rows down the outside of the leaf. The mature larvae assume a curious S-shaped posture around the edge of the leaf when alarmed or not feeding. The good news is that sawfly larvae are not a problem every year. In fact, the last time there was any significant reported damage was in 2003 and 2004. But most years, the damage is so minimal as to be unnoticeable.

If a larvae infestation warrants control measures, and if the tree is small enough, you can spray it. The best insecticides to use are Sevin or one of the pyrethroid products. If your tree is too large to spray, you could hire an arborist to do the job. There are also insecticides containing imidacloprid (Merit), which are designed to be mixed with water and poured on the ground to protect the tree for one season. Usually by the time you notice the problem, it’s too late to reverse.  Thankfully, the birch can recover quickly. It will simply leaf back out either in the same year (if enough of a growing season is left) or the following spring.

So if you have your heart set on a river birch in your landscape, assess your yard to make sure it meets the planting standards, choose the right species and be vigilant about watering. With any luck, you’ll be able to enjoy a beautiful birch for years to come.

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