The Weeds You'll Pull in March Are Sprouting This Month — The Organic Case for a Thick Fall Lawn

A single henbit plant can produce 40 to 200 seeds, and those seeds can stay viable in the soil for up to five years, according to the University of Wisconsin–Madison. That means the purple-flowered patch you notice next March is not a spring problem. It is a fall event you didn't see.

Most of the weeds that show up in lawns in late winter and early spring are winter annuals. They germinate from late summer through fall, grow slowly through the winter, then flower, set seed and die as it warms up. By the time they catch your eye, they have been in the lawn for months.

Which weeds, and when

Extension services name the same short list again and again. Texas A&M AgriLife lists annual bluegrass (Poa annua), lawn burweed, henbit, chickweed, Carolina geranium and rescuegrass among the winter weeds that trouble lawns. Their bermudagrass calendar puts it plainly: henbit and rescuegrass "germinate in late summer/early fall, grow throughout the fall and winter, and then flower, set seed and die in the spring."

Soil temperature is the trigger. Both Texas A&M AgriLife and Clemson Extension note that annual bluegrass germinates when soil temperatures fall below 70°F.

So the calendar date varies by region. The sequence doesn't. Soil cools, seeds wake up, and they look for an opening.

Why bare soil is an invitation

Most weed seeds need two things to get started: light and steady moisture.

Clemson Extension explains that "a majority of seeds need sunlight to germinate," and that healthy turf "shades the soil so that less sunlight reaches the weed seeds." A thick lawn also "minimizes the space available for weeds to become established."

Bare soil gives a seed exactly what dense turf takes away: light on the surface and open ground to root in. Texas A&M AgriLife describes lawn burweed as a winter annual that "germinates throughout thin turf in the fall months as temperatures cool." Thin turf is exactly where you should expect it.

The fewer openings your lawn gives a seed this fall, the fewer weeds you'll deal with next spring.

Mow a little higher, and don't scalp going into winter

Texas A&M AgriLife warns that frequent scalping "will increase the likelihood of weed encroachment by exposing the soil to sunlight that promotes weed emergence and growth." Clemson Extension adds that raising the mowing height in fall "will reduce annual bluegrass seed germination."

Stay inside the recommended range for your grass, toward the upper end, and remove no more than one-third of the blade at a time (Clemson's rule for tall fescue):

• St. Augustinegrass: 2 to 4 inches (Texas A&M AgriLife). Taller mowing brings "shading out of weeds, deeper rooting, and improved water infiltration."
• Bermudagrass: 1 to 2 inches with a rotary mower (Texas A&M AgriLife). Mowing too low "will cause inadequate density."
• Tall fescue: 2½ to 3½ inches (Clemson Extension; NC State Extension gives the same range for fall).
• Tall fescue and Kentucky bluegrass, December–February: 3 inches (NC State Extension).

Deal with thin and bare spots

If you have a cool-season lawn (fescue, Kentucky bluegrass), fall is when extension calendars schedule overseeding of thin areas. NC State's calendar, for example, lists overseeding "thin, bare areas as weather cools." Check your own state extension for local dates.

Warm-season grasses such as St. Augustine and bermuda slow down as it cools, so they won't fill much ground this fall. For these lawns, the job this fall is simpler: notice where the thin spots are, figure out what thinned them (shade, traffic, compaction, a summer of stress), keep an eye on them for seedlings through the winter, and plan to repair them when things start growing again in spring.

Water deeply, and less often

Seeds need consistent surface moisture to germinate. Clemson Extension notes that "deep and infrequent irrigation can help to reduce weeds," and specifically cautions that shallow, frequent watering in early fall favors annual bluegrass.

As temperatures drop, your lawn needs less water. Texas A&M AgriLife suggests that in spring and fall, automatic irrigation "can be turned off in favor of manual watering on an as-needed basis." Water when the lawn tells you it needs it, and water deeply when you do.

Leave the leaves, shredded

Falling leaves are not the enemy. Mow over them.

In Purdue University studies, shredding leaves into grass "didn't affect the color or quality of grass or have any other negative consequences. Nor did it deplete important turf-sustaining nitrogen." K-State Research and Extension reports that, done properly, "six inches or more of fallen leaves can be chopped by the mower and returned to the soil without causing damage."

The goal is small pieces that settle down between the blades, not a whole leaf mat that blocks light from the grass. Shredded, they break down and go back into the soil instead of the trash.

Pull early, while they're small

For the weeds that do get through, your hands are the best tool you own. The University of Maryland Extension calls hand pulling or a weeding tool "the primary means of mechanical weed control in lawns."

Winter annuals are easiest to remove when they're young. Texas A&M AgriLife notes that lawn burweed is "smaller and easier to control" in December, January and February, before it forms its spine-tipped burs in spring. Getting henbit out before it flowers keeps those 40 to 200 seeds per plant from going back into the soil bank.

A note for Gulf Coast lawns

Here, it's the fall fronts, not the calendar, that start pulling soil temperatures toward that 70°F line where annual bluegrass germinates. Lawn burweed is the one to watch in thin St. Augustine; keep your mower between 2 and 4 inches and leave it on the higher setting for the rest of the year. For your fall feeding, the signal hasn't changed: once overnight lows drop into the 60s, apply one to two weeks after that first front. The season runs well into November, and you can order anytime.

Where feeding fits

To be clear: no fertilizer, organic or otherwise, is a weed killer, and nothing we sell prevents weeds. What feeding does is support the grass that shades the soil.

Turf density is a biological result. Roots, soil microbes and organic matter work together over months to build a lawn that fills in and holds its ground. That work is slow, and it happens underground, long before you see the difference on top. Our Soil Biology Guide and The Soil Food Web, Explained Simply walk through it.

MicroLife Liquid Lawn Monthly is how we keep that biology fed without a pile of bags in the garage. Each month you get two bottles, MicroLife Bio-Matrix 7-1-3 and MicroLife MicroGro Liquid AF, applied March through November. They attach directly to our custom hose-end sprayer, which comes free with your first shipment. It ships free in the lower 48, and application takes about 15 minutes on a small lawn, longer on a larger one. You can cancel anytime.

If you'd rather add a single product to your fall routine, MicroLife MicroGro Bio Inoculant (9 LB jug, $38.99) and MicroLife Humates Plus 0-0-4 (9 LB jug, $35.99) both ship; shipping is shown at checkout.

Questions about your lawn, your grass type or your thin spots? Call us at (281) 317-7919. We're glad to talk it through.