Spring Lawn Care – Aeration, Fertility and Crabgrass Control

Early spring is an excellent time to give home lawns a jump-start with aeration and fertility. Cool-season grasses, such as bluegrass, fescue and ryegrass, grow favorably during the cooler weather of spring and fall. Improving air, water and nutrient movement through the soil during this time significantly increases the quality of the grass.

Aeration reduces soil compaction, increases air exchange and allows water to infiltrate more quickly into the soil profile, therefore creating better root mass. Increasing root mass at this time of the year greatly improves the chances of cool-season grasses to reduce stress and survive the heat of the summer.

Aeration equipment can be found at local rental stores or garden centers. A machine that pulls a ½” diameter plug three to four inches deep on four inch centers will do an excellent job. Machines that force hollow tines into the soil are better than pull-type drums with tines. Not all machines will meet these specifications; however, any amount of aeration is better than no aeration.

Applications of fertilizer after aeration will move nutrients immediately into the root-zone of your lawn. This practice has shown excellent results in the density and color of cool-season turfgrasses in preparation for summer stress.

Fertilizer types available to homeowners come in a wide variety. Most are considered quick release forms, meaning they are readily soluble and immediately available to the plant. Any one of these would work for early spring applications. Applying ½ to 1 pound of nitrogen per 1,000 square feet would be acceptable from early March to early April. All fertilizers sold over the counter will have recommendations for rate of application, usually based on square footage. In that case, it would be important to know the square footage of your home lawn and to make sure the proper amount of fertilizer goes down per specified area.

When caring for your lawn and trying to keep it “weed-free,” the saying that “the best defense is a good offense” holds true. Weeds are opportunistic and invade weakened lawns; thus, the best weapon to fight weeds is a dense, healthy stand of grass. There are several good management practices that give lawns a fighting chance against weeds, such as planting the appropriate grass for a particular location, re-seeding bare areas in the fall, proper fertilizing and correctly mowing and watering. The height of mowing influences competition against weeds such as crabgrass - the higher the cut the lower the crabgrass infestation. Optimum watering practices involve less frequent “deep-soak” watering that encourages a deep, healthy root system and maintains a dry surface area where weeds get their advantage. Frequent light sprinkling encourages shallow-rooted weeds and seed germination.

Crabgrass is a summer annual weedy grass species. It is a coarse, textured grass that germinates in the spring and grows well throughout the heat of the summer. Its wide leaf blades, heat tolerance, and prostrate growth habit make it an eyesore in the lawn and allows it to smother desirable turfgrasses. During the summer crabgrass will produce seed heads even at low mowing heights. Crabgrass plants will be killed by the first hard frost in the fall and will drop their seed heads. In the spring, the new crabgrass seedlings emerge around the previous year’s plant unless this open space is re-seeded during the fall with a desired grass, and a preemergent herbicide is applied to kill the germinating crabgrass seedlings.

Preemergent herbicides are so-named because they must be in place before crabgrass seedlings and other weeds begin to emerge. As a general rule, crabgrass may begin to germinate when daily high temperatures begin to reach 70o F or above. In southern Missouri this may occur as early as mid-March; in central and northern Missouri this may not happen until late March or early April. Highest crabgrass emergence begins to occur as daily high temperatures reach 80o F. Our general rule is that for areas in the southern half of Missouri, application should be made by March 15; for areas north, application should be made by April 15. A natural guide, specific to each year’s fluctuating weather patterns, is to have your preemergent herbicide in place before the yellow bloom’s of the Forsythia have all dropped.

Preemergent herbicides will not kill crabgrass that has already emerged. A preemergent herbicide barrier must be present in the soil surface to kill the crabgrass seedling when its first root contacts the soil. Therefore, it is imperative that the preemergent be applied at the right time and watered down into the soil surface either by light irrigation or rainfall. Many effective products are available, almost all of which are combinations of fertilizer with the preemergent herbicide (or crabgrass preventer) in the same bag.

Many over-the-counter products are available to you at several garden centers, hardware stores, farm centers and nurseries. Crabgrass preventers containing Dimension (dithiopyr), Pre-M (pendimethalin), Barricade (prodiamine) or Ronstar (oxadiazon) are excellent choices for the control of crabgrass, other summer annual grassy weeds and some summer annual broadleaf weeds.

When applying weed control products, read the label directions carefully. Do not over apply, either by excessive overlapping or applying more product than recommended to a specific area. Applying too much product could result in damage to turfgrass roots. Determine the effective application width of your rotary spreader and space out each spreader pass to ensure uniform coverage with minimal overlap. It is also recommended that you apply one-half of the rate required in two directions. This allows better distribution of the particles and avoids striping. Do not spread crabgrass preventers into flower or garden beds; they will restrict rooting of new plantings. The fertilizer supplied in these crabgrass products is usually designed to provide 1 pound of nitrogen per 1,000 square feet. This is an adequate amount of nitrogen for good spring growth. You should not need to fertilize any more during the rest of the spring or summer. Excessive spring and summer fertilization favors shoot growth over root growth, requiring more mowing and resulting in a less stress-tolerant lawn during the summer. For further information on turfgrass and weeds, refer to IPM Guide 1009, Turfgrass and Weeds, through Extension Publications @ 573 882-7216.

Brad Fresenburg, UMC Extension/Research Associate, Turfgrass Research Center, (573) 443-4893