Although it’s warm now, cold weather still possible next month

This has not been unusual weather. It’s the norm. But watch out! February can be dangerous for plants. December 1990 was one of the coldest months on record, but February 1989 was much more damaging to plants.

Be diligent around your garden. Protect tender plants. We can be 95 percent assured that freezing temperatures will not occur after mid-March.

Q. A few months ago you had an article about grapes not growing to normal size. You stated the soil in Southern Nevada lacked a certain hormone that the grapes required. My Thompson vines grow like weeds but the fruit is the size of peas.

A. The hormone is not in the soil but manufactured by the plant. Purchasing and applying this hormone is one of three methods that can be used to encourage larger berries.

The application of this hormone to grapes is permitted for organic production in most cases. However, there are two other methods that will enlarge berry size without the application of this hormone.

These other two methods follow the same principle used for producing larger fruit in tree crops. First, remove fruit from the plant so the remaining fruit becomes larger. This totally organic practice is called “thinning.”

When berry clusters or bunches first emerge in March or early April, thin or remove bunches so only large ones remain spaced no closer than a foot apart. Remove small bunches totally.

Second, when individual berries are about the size of a BB, pinch off the bottom third of the bunch. Bunches of grapes are normally triangular in outline. Pinching the bottom third of the bunch produces a harvestable bunch that is round in outline with much larger berries.

After those practices have been followed, you can use a plant hormone called gibberellin to increase the berry size artificially. This is not a natural process but you are basically giving the berries a “kick in the pants” to get them to elongate more than they would normally.

Warning: Don’t expect gibberellin alone to do the work for you. You must also thin out your grape bunches.

Q. When is the right time of year to trim my crepe myrtle tree and what should be done?

A. They usually do not require much pruning. I noticed from your picture that it is planted close to your house Your biggest problems would be branches growing toward the house and walking under branches that are too low.

Remove branches growing toward the house at a “crotch” (where two branches come together) and remove with a “thinning cut.” A thinning cut is the total removal of an entire branch, leaving no part of it coming from the tree.

Limbs that are too low should be removed if people need to pass under the tree. This should also be done with a thinning cut. Remove limbs high enough to allow traffic under the tree.

Aesthetically, trees look better if you restrict limb removal so the tree’s trunk is exposed for no more than one third of its height. A common problem in pruning large trees in this town is excessive limb removal. Once removed, a large limb and the aesthetics it brings, is lost forever.

Crepe myrtle tends to grow branches too close together and sometimes on top, or crossing each other. Look for these common problems and remove one of the offending branches with a thinning cut, leaving no stub.

Lastly, remove any dead wood or weak growth. Using thinning cuts will help preserve this year’s flower production.

Q. A lot of people are raving about worm castings. What is your opinion?

A. Producing worm castings is a form of composting. Some people add worms to finished compost so the worms do not have to survive the very high temperatures produced during composting.

Another method is to add worms directly to a compost, letting worms mix and digest scraps in the compost heap directly. Either way, the resulting product is a very high grade of compost uniform in size and consistency.

The finished worm compost or vermicompost has a low percentage of nitrogen, phosphorus and potassium among other nutrients as well. The finished product is humus, just like it is in compost.

Humus has many other benefits such as lowering the pH, increasing organic acids that act as natural chelating agents and an increasing biological activity.

So, in a nutshell, what is there not to like? However, producing vermicompost without composting first may produce a product that has more health concerns and weeds than traditional compost.

Q. Should ornamental grasses be divided and if so, when? Would you cut the grass down to the ground in February and then divide it in October or is that too much for the plant?

A. Ornamental grasses are treated slightly different depending on the grass. But generally speaking they are trimmed back to about 2 or 3 inches and dead grass removed from the clump.

Start by cutting back the clump to about 8 to 10 inches. Remove dead grass from the clump gently by lightly pulling with your hands or use a garden rake. Some people advocate burning the clump to free it of dead grass. Be careful if you do this and don’t let it burn too long or get too hot.

Ornamental grasses spread by tillers (side growth from the base), rhizomes or stolons. As they get older, grasses that clump begin to die out in the center. When you see this dead area developing in the center it is time to divide the clump.

Alternatively, if the clump of grass is about a foot in diameter it can be divided.

You would do this in September to October of any year ideally. You can also do this in the spring, about mid-February to mid-March, but fall is best. Divide the clump by cutting through the clump with a sharp, sanitized knife.

Immediately replant the divided clumps in to amended soil. Add compost to the soil when replanting and a starter fertilizer high in phosphorus for good root growth.

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. Send questions to Extremehort@aol.com.