Weeds have less chance in a thick, healthy lawn

The summer heat can create headaches for landscapers and gardeners. When it comes to watering, how much is too much? And what can be done about the sudden emergence of crab grass? These were questions e-mailed to me recently by readers of this column.
QUESTION: "I have 52,000 square feet of sod, it's been very nice and green but this year I have been invaded by crab grass. I have never had this problem before. I had previously used one of those green thumb services but this year I decided to do it myself to save some money. This crab grass grows so fast, so big it's taking over! It has popped up right through my sod. What do you think I'm doing wrong and what might correct the problem?" - Bob
ANSWER: Crabgrass can be a problem for cool-season lawns during the heat of summer. In most cases, the seed is there lying dormant during fall/winter and begins to sprout in spring. Your lawn service was constantly caring for your lawn, using the proper fertilizer, herbicide and correct mowing height. It is worth noting that weeds generally aren't a problem in thick, healthy lawns.
Most people just fertilize and mow their lawns. But, it takes research and a lot of time to achieve a healthy lawn. Fertilizer should be applied (on cool-season grass) in early spring, early summer, late summer, and early fall. Some fertilizer compounds contain herbicides which should be used in the spring season as a pre-emergence.
When mowing, the height will depend mostly on the recommended height set by the seed company for the grass planted. Most are in the 2-4 inch height range, but again it depends on the grass variety. Not enough fertilizer, mowing too closely, drought, insects and diseases can also play a part in the weed problem as well.
This time of year, you may want to visit your hardware store for their recommendation on a post-emergence herbicide for crabgrass that will not harm your lawn. Follow the directions on the packaging. Since you do have a problem with the crabgrass now, you may want to apply a pre-emergence during winter or very early spring.
There are several good books on lawn care at most book stores (maybe even your local hardware store). If you decide to continue to maintain your lawn yourself, you might want to pick one up.
QUESTION: "I have 19 Emerald green Arborvitae, planted about two months ago. I watered them as the nursery man said, for 5 minutes every other day for the first week, then if we had no rain, once a week for 5 minutes each. I also set up a weeping hose around all of them so that I could water them while I was at work. My question is, does overwatering cause the trees to go brown and if it does, will they come back if I stop watering them?" - Patrick Blythe
ANSWER: Plants that are over watered and plants that are under watered can show the same symptoms. Based on what you have told me, yes, I would guess that you are over watering. It is a hard call on how much to water during the heat of summer. My recommendation is to cut back on the amount that you are giving them. A good deep watering every 3rd-5th day will be more than enough during the hottest part of summer. You may need to check the soil at the base of the plants by pulling some of the soil away to see if the root area is moist or dry.
As the weather begins cool somewhat, generally in early/mid September, taper off watering even more to harden off the plants. Cutting down to watering every 7 to 10 days by fall would be good. As fall sets in, you may not even need to water them at all, as well as through the winter. If your fall/winter is drier than normal, you may want to water from time to time. In most regions, fall and winter receive more moisture (through rain and snow) and with cooler temperatures there is considerably less stress on the plants. However, you should not attempt to water during freezing weather.
The Plant Man is here to help. Send your questions about trees, shrubs and landscaping to snipped-for-privacy@landsteward.org and for resources and additional information, including archived columns, visit www.landsteward.org
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