The Lowdown on Lawns: Frequently Asked Questions
By: Susan Littlefield
1. What is the difference between cool-season and warm-season grasses?
Cool-season grasses, such as fescues, ryegrass, and bluegrass, are adapted to cooler parts of the country. These grasses grow best in spring and fall and may go dormant in the heat of summer. Warm-season grasses, such as Bermuda grass, zoysia, and St. Augustine grass, grow most actively during the hot summer months and lose their color and go dormant in the winter.
In the transition zone, which runs roughly across the country from Virginia and North Carolina to northern sections of Arizona and parts of lower California, both cool- and warm-season grasses can be grown.
2. What is the best time of year to seed a new lawn?
The best time to start a new lawn will depend on where you are. Early fall is a good time to sow cool-season grasses in northern areas as the weather turns cooler and rainier and annual weeds are less of a problem. Early spring is another appropriate time to establish a cool-season lawn.
The best time to establish a lawn of warm-season grass from seed is in spring to early summer. Some warm-season grasses such as zoysia and St. Augustine are commonly established with plugs or sprigs, little pieces of the turf itself. Spring to early summer is a good time to plant springs and plugs in many areas.
3. There is a section of my lawn that get lots of foot traffic and the grass is very sparse. How can I get it to fill in?
It's tough to get grass to grow where the soil has become compacted. Aerating the lawn with a core aerator opens holes in the lawn that allow water and air to reach the roots of the grass more readily. You can hire a landscape contractor to core-aerate your lawn or you can rent a core aerator and do it yourself. Spring and fall are good times to aerate a lawn. If a part of your lawn gets repeated heavy foot traffic, consider installing a pathway of paving, gravel, or mulch since it will be a struggle to keep grass thriving in such places.
4. What is the best time to fertilize my lawn?
The most important time to fertilize cool-season grasses is in the fall. Make one application of fertilizer in early fall or, even better, split the application into two early and mid-fall feedings. If your lawn needs an extra boost, fertilize again in late spring, when the grass is growing actively and you've had to mow a couple of times.
Fertilize warm-season grasses in mid-spring, or split into early and late spring applications. Fertilize again lightly in midsummer. You can give an additional feeding in early fall to thicken up the turf, if necessary.
5. How do I know if I need to put lime on my lawn?
Most turf grasses grow best if the soil pH (acidity or alkalinity) is between 6.0 and 7.5. If your soil has a lower (more acid) pH, you may need to add lime periodically to raise the pH or ″sweeten″ the soil. This is the case in many eastern parts of the country. The best way to know if, and how much, lime your soil needs is to do a soil test. Lime can be spread any time the ground is not frozen.
6. What is thatch and what should I do about it?
Thatch is a layer of living and dead grass and roots that forms between the live green parts of the turf and the soil. A moderate layer of thatch (¼ to ½ inch thick) is nothing to worry about and can actually benefit the grass, but a thicker layer can interfere with water, air, and nutrients reaching the grass. Thatch occurs when the plant parts accumulate faster than soil microorganisms can break them down. Some of the warm-season grasses are prone to thatch accumulation because they spread by underground and aboveground stems (rhizomes and stolons). But the formation of excessive thatch is encouraged by over-fertilizing, especially with quick-release nitrogen fertilizers; soil that is too acidic or too alkaline; frequent watering; and excessive use of lawn pesticides and herbicides that harm the beneficial soil microorganisms.
One thing that doesn't contribute to thatch is grass clippings. Leaving the clippings on the lawn when you mow adds nutrients and organic matter back to the soil, decreasing fertilizer needs and benefitting the lawn. Mow frequently enough so that clippings aren't so thick and heavy that they mat down over the lawn.
The easiest way to deal with an existing thatch problem is to remove the excess thatch with a machine such as a core aerator, power rake, or vertical mower. You can hire a landscape contractor to do this or you can rent the machine and do it yourself. You can also remove thatch by hand with a bamboo or wire rake.
To prevent excess thatch from forming, use good lawn care practices. Don't over-fertilize, and use fertilizers with organic or slow-release forms of nitrogen. Water deeply, then let the top of the soil dry out before rewatering. Mow at the recommended height for your grass to encourage deep root development. Check the soil pH and adjust if necessary. Rake in a thin layer of compost over the lawn to encourage a healthy population of soil microorganisms.
7. How often should I water my lawn?
How often to water will depend on many factors -- your climate, the weather, the type of soil you have, the height at which you mow (lawns mowed high have deeper roots and need less frequent watering). But here is some general advice that applies in all cases.
- Water deeply when you do water, enough to soak the entire root zone, then let the soil dry out before you water again. If your footprints show when you walk across the lawn, it's time to rewater.
- Don't put down water faster than your soil can absorb it. If you see puddles forming, stop watering and wait for the water to soak in before adding more.
- Water in the morning so that the grass is dry before evening. You'll lose less water to evaporation and have fewer lawn disease problems.
8. How often should I mow my lawn and how high should I cut the grass?
Mowing grass high keeps it healthier. It encourages the formation of deeper, more robust, and more drought-resistant root systems and reduces weed problems by shading out germinating weeds. The optimum height depends on the type of grass you're growing. Most cool-season grasses do best if mowed at 2 ½- 3 inches high; most warm-season grasses at 1 ½ to 2 inches. Be sure to mow frequently enough so that you are not removing more than one-third the height of the grass blade at each mowing to avoid stressing the grass plants, and leave the clippings on the lawn to recycle nutrients back to the soil.
9. Crabgrass is taking over my lawn. What can I do to control it?
Following the lawn care practices recommended above for watering, fertilizing, and mowing will help keep your lawn dense enough to resist many weeds. Crabgrass is an annual weed that grows from seed each year. You can prevent the germination of its seeds with the properly timed application of a pre-emergent herbicide. For gardeners wishing to avoid chemical herbicides, corn gluten, a natural product, can be used as a pre-emergent. To be effective, the herbicide must be in place before the soil warms up enough for the crabgrass seeds to sprout. Check with your local Cooperative Extension Service, Master Gardeners program, or knowledgeable garden center staff for the proper timing for your part of the country. Don't use a pre-emergent herbicide where you plan to sow grass seed; it won't harm existing grass plants, but it will keep grass seed from germinating.
10. When is the best time to put down lawn insecticides to control grubs?
Lawn grubs that feed on the roots of grass plants are the larval stage of various beetles, such as Japanese beetles, Oriental beetles and European chafers. A healthy lawn can tolerate a moderate level of feeding by grubs, so keeping your turf grass robust with sustainable practices that focus on healthy soil will help keep grub damage below the threshold where treatment is needed. Enriching the soil with organic matter and avoiding the use of chemical pesticides and herbicides will encourage the thriving populations of soil organisms that help keep grub numbers in check in the soil ecosystem.
Check to make sure you actually have a grub problem that warrants treatment before applying grub control. In spring and fall, lift off a square foot of turf in a few spots on your lawn and count the number of grubs you see. If you see fewer than 10 or 12 per square foot, you probably don't need to apply grub control.
Milky spore disease powder is a microbial insecticide for the control of Japanese beetle grubs specifically. It is most effective in warmer parts of the country, but has not been shown to afford very effective control in colder northern soils. Beneficial nematodes offer more promise, but need to be selected and used properly. Your soil should be warm (around 70 degrees) when you apply nematodes and you should water them in and keep the soil moist for at least a week after applying them to your lawn. Contact your local Extension Service for more information on the best nematodes species to use and the timing and method of application for best grub control in your area.
There are also a number of different chemical grub control insecticides available for severe infestations. Which product to use and time to apply it depends on the type of grubs doing damage, the particular product used, and your geographic location. The most effective controls are generally applied in mid to late summer to prevent the build-up of damaging populations by targeting young, newly-hatched grubs. Treatments in spring and fall to control active infestations, often in response to lawn damage by animals like skunks digging for grubs, use faster acting products that are effective against older grubs. Consult your local Cooperative Extension Service, Master Gardeners program, or knowledgeable garden center staff for advice on the appropriate products and timing of applications in your area, and read and follow all pesticide label instructions and precautions.