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Make sure you need lawn chemicals to control grubs

By Jeff Rugg

Q: I was wondering about grubs. We were told last fall that our yard had grubs. When do we start to treat them this spring?

A: How bad were the grubs in your lawn last year? Most people are caught up in the hype of killing every grub, when in fact most grubs do little harm.

Almost every yard contains grubs in the fall. More than a half dozen species of beetles have a grub stage in their life cycle, plus cicada larvae and other insects. They are found in lawns and flower beds. Until enough of them are located in one area (10 grub larvae per square foot of lawn), there is no need to use chemical controls. In fact, applying unnecessary poisons to your yard doesn't make much sense.

In the spring, the grubs that were in the soil last fall will move closer to the soil surface from their winter location--down a few feet in the soil. They do a little feeding on grass roots, but rarely enough to harm the grass.

After a few weeks of feeding once the weather warms the soil, they will pupate and become adults in May, June or July, depending on the type of beetle. Lawn chemicals don't work well on the pupa or adults. Adults fly for miles around; killing spring grubs in your yard will not affect how many beetles will fly in from elsewhere to lay eggs for the fall portion of the life cycle.

There are chemicals sold in the spring that claim to give seasonal grub control. For most people's lawns, that means there is a season of chemicals on the lawn that are not needed.

During June and July, adult females prefer to put their eggs on irrigated lawns but not under trees. If you let your lawn dry out and go dormant, or if it is located in the shade of trees, there are usually not enough grubs in the fall to need chemical treatments. Female beetles want to give their babies green grass roots to eat--besides saving water, dormant lawns have fewer grubs and less need for chemical treatments.

Grub numbers differ from one year to the next. Large amounts one year has no bearing on how many will be present the next year or whether chemical treatments will be needed. If many adult beetles are noticed in July, then a treatment in August might be warranted; however, it is better to wait until August to check for grubs before deciding to treat.

During wet summers, the eggs are put so far apart in the grass that the grubs cause little harm. During cool summers or very hot summers, grubs die from diseases and drying out.

Unless your lawn had a huge number of grubs last year, I wouldn't recommend any treatments this spring. A huge amount of grubs could, in theory, possibly do some damage to the grass roots this spring, but, even then, if the lawn is watered by spring rains, it should do fine.

Q: I bought a half-barrel to use as a planter, but it does not have drainage holes. Do I need holes in the pot or can I just add some gravel to the bottom for drainage?

A: If you think you might use the pot in the future for water gardening, I would not add the holes. Otherwise, you should definitely drill the holes. Gravel in the bottom of a pot does not help the drainage in a pot.

In fact, adding gravel to the bottom of the pot or the planting hole, if planting in clay soil in the landscape, actually worsens the drainage in the soil where the roots are growing. Water moves through the soil in large and small pores. Large ones, like those made by worms, can move water quickly; they allow air to move in the soil too.

Small pores can be microscopic in size, permitting water to be retained in the soil for plant roots. Water has surface tension that connects the molecules together. When water moving in a pore reaches a larger pore, it does not automatically go into the larger pore. It must build up pressure behind it in order to overcome the surface tension and move into the open space.

Imagine a large flat sponge. It has many large and small pores just like soil. Submerge it in water to get all the air out of the pores. Take it out of the water and you will see water flow out of the large pores. Then it will stop--you can see water hanging on the bottom of the sponge. The lack of water pressure in the sponge means the water can't move into the open space below. The top 80 percent of the sponge will be damp, but the bottom 20 percent of the sponge will remain saturated and waterlogged.

The same thing happens to the soil above the gravel in the pot or hole; water pressure in the soil will not be strong enough to force the water into the large pores between the stones below. The soil above the gravel will be waterlogged and drown any roots in that area.

If the soil is similar in texture, it will allow the water to wick its way through. If the water can move out, then air can come in. Roots need both air and water for healthy growth. If you want to improve clay soil in your landscape, add organic matter and mix it into the clay to improve the pore space.

If you are only planting some annuals in the half-barrel, they do not need the whole barrel full of soil. Filling the bottom half of the barrel with Styrofoam peanuts or another lightweight filler can make the barrel easier to move, but still gives the plants enough soil. Use a weed barrier cloth between the soil and the peanuts. Or put them in plastic bags so they do not become clogged with dirt.

Use lightweight potting soil that contains large amounts of organic matter in the half-barrel. It will retain moisture in the small pores and still allow for drainage. Potted plants have less room for roots to grow--lack of water is usually the most critical factor.