What’s bright green, has wide blades, is an annual, returns from seed year after year, grows from a central rosette, and flings itself across desirable turf grass, robbing your lawn of light, nutrients and space? Digitaria sanguinalis or Digitaria ischaemum… large hairy crabgrass or small smooth crabgrass. Here in New England, we can encounter both, but the basics and management techniques are identical.
Prevention vs Control…
Prevention is best accomplished by employing some of the suggestions below, and/or through application of a seed germination inhibitor, either natural or chemical.
Control is after the fact… controlling the grassy weed after germination and before it goes to seed. There are no selective, organic alternatives for this application, although there are several chemical options.
Factoids: Crabgrass is a monocot (plants with a single seed leaf, in contrast to dicots... broadleaf and vining weeds with two seed leaves) and a member of the same family as corn.
Each crabgrass plant sends out
70-100 tillers during the course of the growing season. In late summer/early fall seeds are released, up to 150,000 seeds per plant. Seeds buried deep in the soil remain viable for years... when you renovate a lawn or till the soil for any reason, seeds thus exposed to light and moisture will germinate early in the next growing season.
In our corner of New England, soils are slow to warm each spring, so crabgrass is later germinating than in many localities. Once soil temps reach 60 degrees and remain there for about a week, dormant crabgrass seeds start to germinate... germination continues deep into the summer, with many smaller plants in evidence by late summer. However, it is the earliest germinating seeds that produce mature, seed-bearing specimens that ensure a bumper crop for the following spring.
Make crabgrass an unwelcome guest in your lawn, by learning what it likes… then go in a different direction. When all else fails, we turn to organic or chemical preventatives, or post-emergent chemical control.
pH: Crabgrass thrives best at the lower end of the pH scale, with 4.8 being ideal. Your lawn performs best at 6.5 - 7.0. New England soils tend to be somewhat acidic. A simple soil test will indicate where on the pH scale your lawn is… and the appropriate amount of lime to sweeten your soil, bringing it up to that 6.5 - 7.0 ideal turf grass range.
Overcrowding: A desirable action when it comes to crabgrass. A thick, tight turf will not only prevent crabgrass from gaining a foothold, it will prevent many other errant weed seeds from getting established. So, whether you turn to traditional lawn care programs or favor organic options, it’s all about maintaining a dense lawn. A dime-sized space is enough real estate for the tenacious crabgrass seed. Keeping your lawn thick and full, right out to driveway and walkway areas, eliminates prime crabgrass territory. Soil in these areas is often loaded with ice-melting salt, which can kill plants and lawns edges, adding acidity as well. Cue the crabgrass! Apply garden gypsum, at 15# per 100 sq ft, every fall and spring, to neutralize the effects of road salt.
Timing: What I worry about, in chatting with fellow gardeners, is that many are purchasing chemical crabgrass preventatives in early April with the intention of applying almost immediately. Even the traditional timing, when forsythia blooms shatter, can be a tad early. Your crabgrass prevention needs to be in place, but still viable, if it’s to work properly. Such products last about six weeks in the soil, becoming progressively weaker, until their efficacy has dwindled to nothing at the end of the six weeks. (Read on to check the advantage of products that contain “Dimension.”)
Granted, there are variables like erratic spring weather patterns and lawn orientation. A hot, sunny, south-facing lawn will see earlier crabgrass germination than will cooler areas.
Let’s explore prevention and controls…
With the following products, we are concentrating on halting crabgrass seed germination. We carry lawn products from Espoma, Jonathan Green and Greenview… best on the market, in our opinion.
#1…Go Organic! "Corn Gluten Weed Preventer plus Lawn Food" Non-selective prevention. This one actually halts all seed germination, so crabgrass, grassy weed, and invasion by vining or broadleaf weed seed is prevented. Since it is non-selective, corn gluten cannot be used if you’re reseeding or starting a lawn from seed. With a 10-0-2 formulation, you have a first spring feeding high in nitrogen for greening, with a little potassium for roots. Bag recommendations indicate that the best prevention with this corn by-product, for the widest range of weed prevention, comes with 4 applications per year… early & late spring, as well as late summer and early fall. If you use this product, allow about 3 months before reseeding, which probably brings you to a fall (Labor Day) time frame.
#2…"Green-Up Lawn Food with Crabgrass Preventer" Non-Selective prevention. Prevents crabgrass, many grassy weeds as well as a few vining and broadleaf weeds from germinating. As you might suspect, you cannot use this product when starting a seed lawn or reseeding established turf. Long-lasting “Dimension,” the active ingredient, allows later application than most other pre-emergents. Not only is germination suppressed, but young, emerging crabgrass seedlings are contact controlled for up to 4 weeks after germination commences. If reseeding is planned, wait 3-4 months; otherwise, germination of turf grass will be hindered. The 20-0-3 fertilizer will green up winter weary lawns and give roots a boost.
#3…"Crabgrass and Weed Preventer for Lawns and Landscape Areas" is selective, halting germination of crabgrass, some grassy weeds, along with certain broadleaf & vining weed seeds. Like our #2 product, the active ingredient is "Dimension," offering long-lasting control…young, emerging crabgrass seedlings are contact-controlled. This contact feature only applies to crabgrass…other grassy, broadleaf and vining weeds can only be prevented in the seed phase. If reseeding is planned, wait 3-4 months; otherwise, germination of turf grass will be hindered. With a 0-0-7 formulation, nutrient value is minimal, giving a potassium boost to encourage grass roots.
#4…"Crabgrass Preventer plus New Seeding Lawn Fertilizer" Selective prevention with “Tupersan” (Siduron) This product will allow your lawn seed to germinate, while halting germination of crabgrass seed. Do not disturb this barrier by raking, which will then allow crabgrass seed to germinate. It is the final step in a lawn renovation or reseeding project and should be watered in (1/2" of rainfall or irrigation) within 3 days of application, to facilitate barrier formation. At 10-15-10, the fertilizer is nicely balanced for root production and greening. Past customer experience tells us that two applications of Tupersan provides greatest suppression.
Prevention and Contact Control…
#5…"Fairway Formula Greenview Spring Fertilizer Weed & Feed Crabgrass Preventer" Non-selective crabgrass prevention (longer lasting prevention with "Dimension") along with contact broadleaf & vining weed control (2,4-D, Mecoprop-p, Dicamba). Applied between late April and early June, this one product will feed (24-0-6) and prevent/control most of your would-be herbaceous lawn invaders. Obviously, since it’s non-selective, you cannot reseed with this product. Apply to a damp lawn, so contact weed killer clings to weed foliage… should remain undisturbed by irrigation or rainfall for 24-36 hours. Allow three days before mowing. (Wait 2-3 days after mowing to apply.) Any reseeding should be delayed for 3 months after application. If applying to newly seeded lawn, wait until after 4th mowing.
#6… Bonide "Weed Beater Plus Crabgrass & Broadleaf Weed Killer." Post-emergent, contact killer…controls crabgrass (Quinclorac) broadleaf weeds, and vining weeds (2,4-D & Dicamba). This is available as concentrate in a hose-end sprayer or in a ready-to-use quart sprayer. Seed lawns need to be strengthened through four consecutive mowings before this is applied. You cannot seed at the time of application; in fact, allow about three months to elapse before any seeding is done (this is true for any product containing 2,4-D). Do not apply to a drought-stressed lawn and choose a dry period for application, so product has time to provide that contact control. If planning to use in landscaped beds, do so with care, checking the bag for their very specific recommendations.
#7… Bio-Advanced Extreme Crabgrass Killer (active ingredient is Fenoxaprop-p-ethyl). A new, specialized solution available only as concentrate in a hose-end sprayer. Rainproof in one hour! Quickly and efficiently contact-kills hairy or smooth crabgrass plants. With this product, reseeding can occur as soon as two weeks after application.
Application Note re: any pre-emergent or contact control: It’s a good rule of thumb to wait 2-3 days after mowing to apply any herbicide and wait another 3-4 days before your next mowing. The initial waiting period allows cut grass blades to reestablish their protective cuticle-like coating, protecting freshly cut ends from chemical damage. Waiting to mow after application allows the product to form a barrier across the soil, without disturbance.
If it’s early spring and you’re seeing "crabgrass" in the lawn, it’s NOT! As discussed earlier, true annual crabgrass does not begin germination until we have sustained soil temps around 60º (see crabgrass basics), so any other wide leaved grassy weed is in evidence during March or April, it is most likely a perennial grass, like coarse wild fescue.
Crabgrass remains the most persistent invader of lawns; however, here are a few grassy weeds that, in some cases, loosely imitate crabgrass in appearance and are potential invaders of lawns and gardens. In many cases, germination of the following is also inhibited by application of a crabgrass preventer... check individual products for complete lists.
Annuals: Barnyardgrass, annual bluegrass, roughstalk bluegrass, large crabgrass, smooth crabgrass, Dallisgrass, yellow foxtail, green foxtail, giant foxtail, goosegrass, Japanese siltweed, fall Panicum, Wild proso millet, witchgrass, and wild oat.
Perennials: Bermudagrass, coarse wild fescue, nimblewill, quackgrass, and wirestem muhly. While corn gluten or other preventatives may halt seed germination, these are perennial weeds, with no selective control available for mature plants... digging them out or spot-treating with non-selective applications, followed by reseeding (check package for timing) is about the only solution.
Prevention: Many of the above annual specimens can be prevented in the seed phase. Post-Emergent Control: Bio-Advanced Extreme Crabgrass Killer contact-controls some of the other grassy weeds listed above, as well as crabgrass.
Herbicide Reminder: About herbicide application, in general... check individual packages for warnings but, generally speaking, avoid application to drought-stressed lawns and when temperatures are expected to soar above 85 degrees. While we're concentrating on spring preventative applications, drought and high temps are an unlikely scenario. However, summertime application of contact-controls for crabgrass, vining, and broadleaf weeds, brings us in direct conflict with these difficult conditions... proceed with caution.