Take care when applying lawn fertilizer in the spring.
By Dave Minner
Extension Turfgrass Specialist
Iowa State University
Spring is here and a few things done now will help your lawn deliver the appeal and durability that you expect during the summer. Lawns fertilized last fall will green up quicker this spring; a little nitrogen in April or May will help those lawns that didn’t get fertilized last spring.
A soil test should be taken to determine the need for phosphorous. Most of the soil tests that I see show that Iowa lawns don’t need additional phosphorus. Apply it only if it is required or if you are planting grass from seed. Using phosphorous wisely and efficiently reduces the phosphorous load in our lakes and streams.
Extra care should be taken when applying any fertilizer or pesticide to the lawn. The lawn is like a sponge and is very good at trapping water and reducing runoff, but it does no good if lawn care products are spread onto hard surfaces like sidewalks and driveways and then washed into the storm water drainage system. Do your part to sweep or blow granular products back into the lawn where they stay put.
After things have greened up and the lawn has been mowed twice, it will be time to look for broadleaf weeds. It’s hard to miss the yellow flowered dandelions that are a clear indicator of weeds taking over the lawn.
Your goal should be to use a broadleaf herbicide on the entire lawn until weeds are reduced to about 10 percent of the total area; then just spot treat the individual weeds. Liquid herbicides provide better coverage that usually leads to more effective weed control. Granular weed and feed products are more convenient, but it is important to apply them when the lawn is wet, so that the dry pellets stick to the wet leaves, allowing uptake of the herbicide by the weeds.
Another important weed that lurks in nearly all lawns is crabgrass. If you had crabgrass last year, then you surely will have it again this year because it reseeded itself last fall. In this case pre-emergence herbicides are your best choice to kill the young crabgrass seedlings before you even notice them in May. Pre-emergence crabgrass products need to be applied by April 15 to be sure that the product is in place before crabgrass begins to germinate as soil temperatures approach the low 50 F mark.
Crabgrass first shows up along sidewalks where the turf is thin and soils warm faster. If you don’t anticipate much crabgrass in your lawn, then you can skip the pre-emergence application and wait until late May or early June to see how much crabgrass invades. Lawn care companies often use this strategy to reduce the pesticide footprint. If needed, they use a product called Drive in mid-summer to control crabgrass after it develops and becomes obvious in the lawn.
As temperatures continue to warm and the grass grows a little faster, count on mowing the lawn each week at a cutting height of 2.5 inches. This helps you from violating the one third mowing rule; never remove more than one third of the plants' total height. Clippings that are 1.0 to 1.5 inches long easily filter into the turf canopy and do not need to be bagged. The clippings actually add nitrogen fertilizer back into the lawn and help feed worms. There’s no need to fill the landfill with perfectly good worm food; it makes it hard for them to go fetch it.
A final strategy in spring lawn care is to not start watering too soon. This is sometimes difficult for those with automatic irrigation systems since they are anxious to get started on the irrigation season. It is best to wait until the lawn starts to naturally wilt in the summer before you start to irrigate. A little bit of wilting does not hurt the lawn; in fact, wilting signals the plant to grow more roots deeper in the ground that will help during extended dry periods later in the summer. You are wasting water if you irrigate before the lawn starts to wilt. Once the lawn watering season begins, then your goal should be to water deep and infrequently. Lawns usually need about an inch of water per week. Apply your water in one or two days and then try to wait a week until the lawn starts to wilt again.
Developing your lawn care strategy early in the spring will let you sit back and enjoy the green green grass of summer.
David Minner, Horticulture, (515) 294-5276, firstname.lastname@example.org