Get Growing with Val!
One of the most frequently asked questions I get in the Spring time is "How do I get rid of Crabgrass?". Yes, that pesky little weed is a real brute and quite difficult to control once it gets growing so the real key to "controlling" crabgrass is to not let it get established to begin with! In other words....an ounce of prevention is worth a pound of cure. I'll explain: but first a few important facts to know about Crabgrass that will give you a better understanding in how to manage it.
1) Crabgrass loves the sun. That being said, it will only be a problem for you in sunny areas of the lawn so you don't need to think about "control" in your shady areas. (See...if just got easier already!)
2) Crabgrass is extremely drought tolerant which explains how it survives even in lawns receiving no little to no irrigation.
3) Crabgrass needs no fertilizer. It thrives in what ever little nutrients are found in even the poorest of of soils.
4) Crabgrass is actually an annual weed. "Annual" means it grows for only one growing season, dying in the winter months and coming back from (last years) seeds to start all over again.
So in a nutshell, if you've had crabgrass, you would have noticed all of the above....it's in the sunny areas of the lawn, especially in areas with poor soil and little irrigation like along the edges of the driveway or down by the road where maybe your sprinklers and fertilizers don't reach as well. It will thrive where the grass is weak. It will grow all summer and then in the fall it will produce seed heads and drop those seeds to the soil surface. The seeds will sit there all winter and wait for warm soil temperatures the following year and will then germinate and start all over. A well fed and well watered lawn will have much less of a problem with Crabgrass than a healthy, thick turf as a healthy and thick turf leaves little room for Crabgrass to take off. Once it germinates (late Spring/early Summer) it grows rather quickly with long and fairly wide blades of grass-like leaves that lay flat instead of growing upright. As they spread out they "shadow" the grass beneath it almost like it's smothering it thus preventing the grass from getting its much-needed sunlight. This weakens the grass in that area thus strengthening the Crabgrass even more! There are post-emergent (meaning Cragbrass seeds have already germinated) Crabgrass controls but their effectiveness is spotty at best. (If you looked at a leaf of Crabgrass under the microscope you'd be able to see tiny little hairs on the leaf. These little hairs actually help protect the leaf from any post-emergent controls as they "repel" any spray or granule you may try to apply to kill it!) The only real effective control is a pre-emergent (before the seed germinates) control. We have both chemical and organic controls you can consider.
Crabgrass seeds will germinate when the soil temperature rises to a little over 50 degress F. That also happens to be the same soil temperature that forces the flowers on a Forsythia bush to open. You may have heard it said that the right time to apply a Crabgrass pre-emergent is when the Forsythia bushes are flowering. Well that's why we use that as a guide, because when the Forsythia is in bloom, we know the soil temperature is ripe and the crabgrass seeds are about to crack open. Pre-emergent crabgrass controls are sold in bags, like fertilizer, and are spread with a spreader the same way you would apply fertilizer. Most pre-emergent Crabgrass controls are bagged WITH fertilizer so in one step you are feeding and controlling. This type of product is generally called "Step 1" as it's usually the first application you make to your lawn in the Spring. The fertilizer portion of the bag feeds the lawn as it's waking up from winter and the Crabgrass control portion of the bag will lay on the soil surface, covering the surface like a blanket. When a Crabgrass seed cracks open and sends out it's first leaf and root, it comes into contact with the "blanket" and dies. It's your ounce of prevention! There are two types of chemical "Step 1" products. The "Regular" and the "Seed Starting" versions. You cannot simultaneously plant grass seed in the Spring if you are applying the regular Step 1 product as it will also not let grass seed germinate. If you want to control crabgrass AND plant grass seed, then you must use the "Step 1 For Seeding". Here, the makers of the product have switched out the regular Crabgrass control and substituted it with a Crabgrass control that is safe for newly planted grass seed. A "Step 1 for Seeding" product will be more expensive than the regular Step 1 but if you have to apply grass seed while controlling Crabgrass, it's the only way to go!
As for an organic Crabgrass control, we have Corn Gluten. Corn Gluten is a good organic source of Nitrogen (the nutrient that promotes growth and turns plants green) but applied at a high rate, is also a very effective pre-emergent Crabgrass control as it will not let seeds survive germination. (This includes grass seed, too, so you cannot plant grass seed when using Corn Gluten!). In fact, Corn Gluten lasts so long, you can't apply grass seed for the balance of the growing season! You can Google "Corn Gluten as a Crabgrass Control" for more information. It is great to have this organic alternative as it is safe for people and pets and it feeds as well as it prevents Crabgrass.
So, to re-cap, mid-April is typically when the soil temperatures rise to 50 degress F or above, as will be evidenced by the blooming of the Forsythia bush and that is when it's imperative you have one of the above Crabgrass controls applied! I want to mention, that if you have any raking, thatching or plugging to do to the lawn, YOU MUST do this BEFORE you apply the Crabgrass control, for once it's applied you DO NOT want to disturbe the "blanket" of Crabgrass control on the lawn! Once applied, and for the balance of the season, keep your lawn well fed and well watered....remember, a thick and healthy lawn will come to your aid by not leaving any room for Crabgrass to get started.
It's worth mentioning a little about watering here.... I mentioned earlier that Crabgrass is quite drought-tolerant. When you do water your lawn, it's important to water deeply! Grass roots are 4-6" deep and only a good saturation will reach this level. On a hot day, a twenty minute watering will do more harm than good! The water from a twenty minute watering will not penetrate the soil deeply enough to benefit the grass. The Crabgrass, however, will love it! So be sure not to bother watering if you can only water for twenty minutes. Try putting a rain guage in the lawn area. If you're watering delivers an inch of water, you're good! Less than that generally only benefits the weeds!
Stay tuned for what to do about Broadleaf Weeds, such as Dandelion, Clover, Chickweed, etc. Broadleaf weeds are an entirely different group of weeds and there are some basic understandings you need to have to be successful in controlling them!