Taper of the trunk indicates tree’s strength

Q: I have read that African sumacs are fast growers. The African sumacs here seem to be at a stand still. I have had two in my backyard since April. They are alive but the canopy and trunk just seem the same; there has been perhaps 10 percent growth. The trees are solid with tall, thin trunks, about ½ to ¾ inch in diameter, with a canopy that branches out at 8 feet. There are no branches or leaves below that. The trees are staked high and the stems are all finger diameter. Will they take off eventually?

A: Trees with long, skinny trunks with no side branches until 8 feet are a problem. This is done at the wholesale nursery to increase their height and make it easier to ship. It is to their advantage, not to yours.

To have strong trunks, tree trunks should be tapered from top to bottom. In other words, to have good trunk strength the trunk needs to be bigger in diameter at the bottom and get narrower up toward the top. This helps to support the canopy. If they don’t, a good wind will come along and snap the trunks.

Trees develop tapered trunks from two major events in their lives: trunks swaying back and forth in the wind and the presence of branches with leaves all along the trunk. Both have a great deal to do with trunk taper and consequently its strength.

When trees are staked, trunks should be immobilized no lower than it takes to hold the tree upright and still allow some trunk movement. The stakes should be removed as soon as possible after planting, usually no longer than one full season of growth.

Next, never remove branches growing along the trunk if they are smaller than pencil diameter. Once these stems reach pencil diameter or thereabouts, cut them off flush with the trunk with a clean, sanitized bypass-type pruning shears. When they are small, they help build caliper or taper.

Never plant in a dry hole. Make sure the soil in the hole is wet when tree roots come in contact with it. Planting in a dry hole can set a tree back, or any plant for that matter, because of root damage.

Sometimes people say this is “transplant shock.” Well, yes, plants do have a setback, or shock, when removed from a container and placed in the ground. This can happen for many reasons but the degree of setback can be under your control.

Why are they growing so slow? The amount of total growth on a plant (add up all new growth above and below ground) is divided by the number of places where growth can occur. Stems in full sunlight or without competition from other branches will usually be the strongest in growth but the total growth must be divided among every place that is growing. This includes the roots and any increase in the diameter of stems and trunks.

If you want a plant to grow faster, reduce the number of places where growth occurs. Prune out unnecessary stems so that the growth is focused on those stems where you want growth to occur.

Q: We actually took off the last tomato early this week. It was not fully ripe, but took we it inside so no bugs or other things would get to it. Somewhere I remember reading that you can cut them back to 12-16 inches and they will grow again.

A: You can cut them back to some side shoots now but it will open the plants to sunburn if you are not careful and the plant may die. It is possible to cut them back now while it is still hot but make your cuts so that you reduce their height and still leave plenty of side shoots.

Another possibility is for next year. Try planting some from seeds in early to mid-July. Put the seeds between the plants and cover the soil and seeds with straw to keep them moist and hand water daily. Make sure you mix compost into the soil in the spots where you planted the seeds. Soak the seeds in water for four to six hours before you plant them. This will speed up germination. In about mid-to-late August, cut or remove your old plants and let the young ones come in for production in September through November.

Stake or trellis the plants and thin side shoots so you have better air circulation. Reduce any winds you have on the area with wind screens or windbreaks. Make sure you have at least six to eight hours of full sun, fertilize lightly every 30 days after you see flowering.

Q: I was wondering if there is a trick to container gardening? I have been using potting soil, along with plant food, and my plants keep wilting. What am I doing wrong?

A: I am not sure what is going on in your case, but container gardening can give you some flexibility in growing things. It also can be a bit trickier because of the limited soil volume, how water moves through the container’s soil and finding or creating the right environment.

Start with a container that is fairly large. Small soil volumes are difficult to keep moist during our desert heat. If the soil dries out, water will flow down the inside of the container wall and not wet the soil properly.

When wetting dry container soil, use a wetting agent with the water. A tablespoon of liquid detergent in a bucket of water will work. Add the detergent after the bucket is full of water.

Always make sure the water can drain from the container directly out of the bottom to keep salts moving through the soil profile. Also, when watering, add about 20 percent extra water (one-fifth of the volume applied) to keep salts moving through the soil or they will build and damage the plants.

At every planting season, replenish one-fourth to one-third of the soil volume with new soil. Make sure the soil is good quality. There is plenty of junk being sold locally and in bags as well.

Shade the container (not the plant) from direct sun during the daytime. You can do this by double potting it.

Use an inexpensive soil moisture meter for houseplants to give you a rough idea if the soil is wet or dry. Otherwise lift or push the container. Containers get much lighter when it is time to water.

Fertilize lightly once every one to two months during the growing season.

If you have trees in containers, gently lift the tree from the container every three to four years, prune the roots, replace the soil, prune the tree to reduce its size and to bring it back to scale before replanting it.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com