Lawn aerator. (Photo: Shutterstock).

Carol O'Meara, Colorado State University Extension

Carol O’Meara, Colorado State University Extension

The warm weather ahead of the bitter cold snap had many people thinking of spring chores. The recent storms with their snowfall were a welcome drink for parched landscapes, and one of the first plants to show their appreciation after the thaw is lawns. They’ll green up, and to get a season of stress-free grass, a few chores now gives you a dense, healthy yard this summer.

First, tackle those pesky weeds. Timing is crucial for controlling annual grassy weeds, whose seeds fell to the soil in fall. Lying quietly on the lawn until spring soil temperatures soar into the 50s, the seeds can sprout and grow quickly before you’re ready to stop them.

Pre-emergent weed control is helpful in keeping weeds at bay, and for best results, plan now to put it on your lawn. The right time to apply pre-emergent weed control is mid-March to early April, two to four weeks before the seeds germinate. Too often the pre-emergent is put down after the seeds have sprouted; weeds already up and growing are unharmed by it.

As with all products, follow the package directions when applying pre-emergent. Regardless of whether it is derived synthetically or naturally, pre-emergents need only be applied in a light layer across the lawn. Put down too much, and there is a risk of stunting the grass’ root system, causing poor performance later in the summer when heat takes its toll.

The jury is out on whether corn gluten is an effective pre-emergent, but if you’re opting to try it, remember that it contains a fair amount of nitrogen. So decrease the amount of nitrogen fertilizer you put on your lawn in the spring fertilization. Too much nitrogen and your lawn mower will become your best friend, since your grass will grow so quickly you’ll need to mow often.

The best defense against weeds is to grow a healthy, dense lawn that will out compete weeds trying to muscle in on your turf. If you have a thin lawn and want to over-seed it with grass this season, do not apply pre-emergent. Spring is a good time to over-seed cool season grasses into areas that are threadbare.

For best results, core-aerate the lawn before you spread seed. The seed will fall into the holes made by the aerator, which act as ideal germination chambers for grass seed. As the seedling sprouts and germinates, its roots dig deeper into soil that has been aerated.

When core-aerating, pass the machine over the area several times in differing directions, making hundreds of holes in the ground. Water the lawn lightly every day until the seed has germinated.

Grass seed is a slow germinator, so be prepared to wait fourteen to twenty days for it to sprout. The most common mistake in over-seeding is from impatience with the germination time – many gardeners give up too soon and cut off the water just when the young sprouts first emerge.

If you have already applied pre-emergent, wait two to four months before trying to over-seed. The pre-emergent will breakdown in the sunlight during the summer months and allow for germination of new seed.

By Carol O’Meara. Carol is an Extension Agent – Horticulture Entomology at Colorado State University Extension Boulder County. For more information call 303.678.6377, e-mail comeara@bouldercounty.org or visit ext.colostate.edu/boulder.