Crabgrass is one of the most commonly named lawn weeds in North America and if you watch the ads in the spring for chemical lawns, you might think this grass and dandelions are the major threats to our way of life.
It’s an Annual Grass
The first thing to understand is that this is primarily an annual grass that sets seed (lots of seed) in one year and then dies off.
The following spring, these seeds germinate, grow and then set seed again before being killed by winter temperatures.
Seeds in the northerly gardens tend to germinate first thing in the spring while southerly gardens can see germination almost all summer long.
A formal lawn surrounded by hedges. This is Royal Roads University in B.C. Canada (they filmed X-men here)
Controlling this Grass Weed
There are several easy methods of killing it.
The number one trick is to grow a healthy lawn. A vigorous stand of turf will outcompete crabgrass and it is primarily a pest of poorly managed lawns.
Organic Weeding and Feeding
A primary technique is to spread corn gluten (it comes in various product names and brand names now) on the yard at the recommended rate of 20 pounds per 1000 square feet.
This product acts to stop small seeds from germinating so if applied when the forsythia come into bloom, it will stop small seeds from germinating.
Given that this is an annual seed, if it can’t germinate every year, it can’t survive on your lawn area.
Mowing Technique to Stop It
Mow your lawn at the highest mower setting.
This allows the other grasses to grow strongly and shade out the crabgrass seeds. Stopping the seeds from germinating is as good a technique as any.
Some studies have shown that lawns that are mowed just over 2-inches tall (instead of the usual 1-inch scalping) decreased the crabgrass on the lawn from a high of 30% in the first year, to a low of 7% in the fifth year.
Feed your lawn at the recommended rates.
Lawns that are low in fertility have higher incidences of this problem grass.
This is not a competitive grass and if you feed the good grasses properly, they’ll out-compete it.
A bit of university ag-research pointed out that an application of 20 pounds of manure per 1000 square feet in the fall and again in the spring gave a 75% reduction in the amount of crabgrass because the other grasses were more vigorous.
Combine All Techniques
If you combine the tall mowing with the heavy organic feeding, you can expect to almost eliminate your crabgrass within 5 years without doing any spraying. The research pointed out that after 5 years of this combined treatment, there was only 2% of crabgrass left on a heavily infested lawn.
Another option is to pick a competitive grass for your lawn. In the northern areas, perennial ryegrass and Kentucky bluegrass are two of the better choices.
Some of the taller fescues are fine but many tend to be dwarf and are easily invaded so unless you know for sure they are taller varieties, stay away from fescues.
Overwatered lawns are also invaded more frequently than those that are properly irrigated.
This is usually because the existing turf becomes weaker with the overwatering or multiple light waterings. You’ll most often find the crabgrass along open areas next to walkways or around sprinkler heads or around any area where the grass is mowed shorter (like around trees).
I have also read the interesting technique of covering the lawn with a layer of black plastic for only ten days when you see crabgrass germinating or heavily infesting a lawn.
After the ten days of darkness, it will be dead. The other grass will be yellowish but not dead and will recover fairly quickly once the poly is removed. I haven’t tried this but it is worth a try if you have a heavy infestation and don’t want to use chemicals.
But the real trick is to have a healthy lawn and grow it properly without the use of chemicals.
You can do this.