Spring pre-emergent
Goes down before summer annuals germinate, as soil warms through the mid-fifties. This is the one that decides how much crabgrass you have in July.
Lawn and property care guide · North Alabama
Weeds, and why timing beats effort
The two pre-emergent windows that decide most of the year, the weeds that show up in Marshall County, and why a thick lawn is the only permanent control.
The principle
Weeds are a symptom before they are a problem
Nearly every lawn weed is an opportunist that needs bare soil and light to establish. A thick lawn gives it neither, which is why the permanent answer to weeds is almost always about the grass rather than about the weed.
This is not an argument against treatment. Treatment is what buys the time for a lawn to thicken, and on a lawn that is already overrun it is the only sensible first move. But if the mowing height is wrong, or an area is compacted, or a corner is in shade it will never grow out of, treatment becomes an annual subscription rather than a fix.
Mowing does not stop weeds. It cuts them, which sets some of them back and encourages others to flower lower down. Plenty of lawns are mown perfectly and full of weeds because the grass is thin, and the thinness is the thing to solve.
The corollary is worth stating: if weeds keep returning in one particular area, that area is telling you something. Shade, drainage, traffic and scalping are the usual answers, and the thin lawn guide works through them.
Timing
Two windows a year, both set by soil temperature
Pre-emergent works on seed before it comes up. That makes it the highest-value work in the weed year, and also the least forgiving: a fortnight late is the same as not doing it.
The spring window comes as soil warms through the mid-fifties, before summer annuals such as crabgrass germinate. The fall window comes as it cools back through the same range, before the winter annuals - poa annua, chickweed, henbit and burweed - get going.
Both are soil temperature events, not calendar dates, and the difference between a warm February and a cold one is real. Watching the ground is the whole skill.
Post-emergent is a different job on different plants: it works on weeds that are already up and visible. The two are not interchangeable. Pre-emergent will not touch a weed you can already see, and post-emergent does nothing about the seed waiting for next season, which is why a sensible program uses both at their own times.
Fall pre-emergent
Goes down as soil cools back through the same range. This is the one that decides how much poa annua and burweed you have in the spring.
Post-emergent
For what is already up. Necessary, but it is catching up rather than getting ahead, and what can be used depends on which grass it is growing in.
What grows here
The weeds Marshall County actually produces
Knowing whether a weed is a summer annual, a winter annual, a perennial or a sedge tells you when the useful work happens. Everything else follows from that.
| Weed | Type | When the useful work happens |
|---|---|---|
| Crabgrass | Summer annual grass | Spring pre-emergent, before it germinates |
| Poa annua / annual bluegrass | Winter annual grass | Fall pre-emergent |
| Burweed / spurweed (stickers) | Winter annual broadleaf | Fall, months before it hurts anybody |
| Chickweed and henbit | Winter annual broadleaf | Fall pre-emergent |
| Clover | Perennial broadleaf | Feed the grass properly; it competes best where nitrogen is short |
| Dandelion | Perennial broadleaf, taprooted | While actively growing. Pulling the top off does not settle it |
| Nutsedge | Sedge, grows from tubers | Fix the wet ground first. Pulling it multiplies it |
Timing and biology only. What is used on any lawn, and whether anything is used at all, is decided on the property - and the label on whatever is applied is the legal instruction.
Two that catch people out
Burweed and nutsedge
These two are worth their own paragraphs because both are usually attacked at exactly the wrong moment.
Burweed - the sticker weed that hurts bare feet in April - germinates in fall, grows quietly through winter looking like nothing in particular, and forms its spiny burs in spring just as everybody starts walking outside without shoes. By the time it hurts, the useful window was months ago. It feels impossible to beat for precisely that reason, and it is dealt with in the fall.
Nutsedge is a sedge rather than a grass and it grows from underground tubers. Pulling it usually makes it worse, because disturbing the tubers is how it multiplies. It also favors wet ground, so a patch of nutsedge is very often pointing at a drainage problem and fixing the water is part of fixing the sedge. Its stem is triangular in cross-section, which is the quickest way to confirm it.
Beds, ornamentals and re-entry
Two questions everybody should ask before anything is sprayed
How close it is to the beds, and how long to stay off it afterwards. Both have real answers, and both should come from the person doing the work.
Drift onto ornamentals is a genuine risk, and the way it is managed is by knowing what is planted and where before anybody starts. Tell the crew what is in the beds, particularly anything you would be upset to lose, and it gets worked around. Bed weeding is a separate service in its own right - see flower bed maintenance.
Re-entry - how long before children or pets go back on the lawn - is set by the label of whatever was applied. That interval is the legal instruction, it varies between products, and it is the only answer anybody should give you. Ask on the day, or call (256) 506-9006, and you will be told what was used and how long to wait. If in doubt, wait until it is fully dry and then a while longer.
And one expectation worth setting: a single treatment rarely fixes a whole lawn. Different weeds germinate at different times of year and respond to different work, so one visit deals with what is there that day. Lawns that get on top of weeds usually do it over a couple of seasons of consistent timing.
Answers
Questions about weeds and pre-emergent guide
When should pre-emergent be applied in North Alabama?
Twice a year, both timed to soil temperature. Spring as the soil warms through the mid-fifties, before summer weeds germinate; fall as it cools back through the same range, before the winter weeds do.
What is the difference between pre-emergent and post-emergent?
Pre-emergent works on seed before it comes up. Post-emergent works on weeds that are already growing. They are not interchangeable, which is why a program uses both at their own times.
Why do I have green weeds in my brown winter lawn?
Those are winter annuals, and they grow when your warm-season grass will not. Poa annua, chickweed and henbit all germinate in fall and run through the cool months.
What is the sticker weed that hurts bare feet?
Almost certainly burweed, also called lawn burweed or spurweed. It germinates in fall and forms its spines in spring, which is why it feels impossible to beat - the useful window is months before anybody notices it.
How soon after treatment can children or pets go on the lawn?
Follow the re-entry interval on the label of whatever was applied. It varies between products, so ask the crew on the day or call the office. If in doubt, wait until it is fully dry and then longer.
Will one treatment fix my whole lawn?
Rarely. Different weeds germinate at different times and respond to different work. Getting on top of weeds is usually a couple of seasons of consistent timing.
Read next
Related reading
Weed Control and Fertilization
A service HRH Lawn Care handles.
North Alabama Seasonal Lawn Care Calendar
From the lawn and property care guide.
Fertilizer, Lime and Alabama Soil Testing
From the lawn and property care guide.
Why a Lawn Turns Brown, Yellow, Thin or Patchy
From the lawn and property care guide.
HRH Lawn Care Services
Not sure what your property needs?
Call and ask. We would rather come and look at it than guess over the phone, and it does not cost you anything either way.