Does clover mean my soil is low in nitrogen?

Yes. White clover competes poorly in a dense, well-fed lawn and dominates in a thin one. Raise the annual nitrogen to the species budget, hold the cutting height at the top of the band, and the clover thins over two seasons without herbicide.

Why do dandelions keep coming back after spraying?

Because the compaction that lets the taproot in has not changed. A dandelion root can regenerate from a 25 mm fragment, so spraying removes the top growth and the root re-shoots. Core aeration and a denser canopy are what end the cycle.

Do I need to treat weeds before overseeding?

Yes, but with the reseeding interval in mind. Most selective broadleaf herbicides require four to six weeks between application and sowing, so treat early in the season you plan to overseed, not the week before.

What is the best time of year to treat broadleaf weeds?

Early autumn, when the weeds are moving carbohydrate down to the roots and the grass is growing hard enough to fill the gaps. Spring treatments work but the lawn is less able to close the gaps afterwards.

symptom reading2026-11-01By The Turf Deskrecovery 8–30 weeks

Broadleaf weeds: reading the indicator species before reaching for a spray

Parameter sheet

Indicator

Broadleaf weed species as indicators of soil and management conditions

Recovery

8–30 wk

Chain of causes

Compacted soil where the taproots of dandelion and plantain can penetrate but grass roots cannot, so the weeds have an exclusive hold.
Cutting height below the species floor, thinning the canopy and letting light reach the soil surface where weed seed germinates.
Soil pH outside the species band, which weakens the grass while the weeds in question tolerate the reading.
Nitrogen below the species budget for several seasons, producing an open, pale stand that clover and speedwell colonise readily.
Surface moisture that stays high, favouring species such as creeping buttercup and moss-adjacent weeds that indicate poor drainage.
A thatch layer over 15 mm that keeps seed in contact with moisture at the surface, which is what crabgrass and goosegrass need to germinate.

Parameter fixes

Core-aerate to 75 mm depth at 50 to 100 mm spacing wherever dandelion, plantain or knotgrass dominate; the taproot species are the compaction indicators.
Raise the cutting height to the species band and hold it for a full season. Density, not herbicide, is what keeps weed seed from establishing.
Bring the annual nitrogen to the species budget: 15 g per square metre for Kentucky bluegrass, 12 for tall fescue, 6 for fine fescue. Clover and speedwell indicate a lawn that has been underfed.
Correct the soil pH to the species band: 200 to 250 g per square metre of lime on a loam to raise half a unit, applied in early autumn.
Scarify 5 mm where thatch exceeds 15 mm and remove the mat, which is the germination bed for summer annual grasses.
Where drainage is the driver, indicated by creeping buttercup or rushes, add a French drain or a surface swale before any other measure.
Overseed at the species rate in early autumn to raise density. A stand at 80 percent cover suppresses new weed germination; a stand at 50 percent does not.
Where chemical control is used, treat only the species present, at the label rate, when the weed is actively growing and air temperature is between 15 and 25 degrees Celsius.

Field confirmation

Read the indicator species: dandelion, broadleaf plantain and knotgrass indicate compaction; clover and speedwell indicate low nitrogen; creeping buttercup and rushes indicate poor drainage; sorrel and sheep sorrel indicate acidity.
Push a screwdriver into the soil where the weeds are densest. Two hands and a stop at 50 mm confirms compaction.
Count the stand: lay a 300 mm square frame in three places and count grass tillers per square metre. Below 3,000 tillers per square metre allows weed establishment.
Measure the canopy closure by looking straight down in midday sun: if more than 15 percent of the view is soil, the stand is too open.
Soil test for pH and phosphorus; weed composition is a hint, not a measurement.

Stand density plot for Broadleaf weed species as indicators of soil and management conditions — Vacancies in the dot matrix are the bare patches; the washed areas are moss or thatch

Most broadleaf weeds are reporting a condition rather than causing one. Dandelion and plantain report compaction, clover reports low nitrogen, buttercup reports poor drainage, sorrel reports acidity. Treat the condition and the weeds stop returning; spray alone and they come back the following season from the same seed bank.

The indicator table

Each weed species occupies a niche that the lawn grass has vacated. That vacancy is caused by a soil condition, a management parameter, or both, and the weed species present tells you which one.

Compaction is the most common, and its indicators are the taproot species: dandelion, broadleaf plantain, buckhorn plantain and knotgrass. A taproot 150 mm long cannot grow in a dense, well-structured loam where grass roots fill the pore space; it grows where the soil is compacted and the grass roots have been excluded.

Low nitrogen produces a pale, open stand, and the indicators are the nitrogen-fixing and low-fertility species: white clover, black medick, and slender speedwell. Clover is not a cause of a poor lawn; it is a report that the lawn has been underfed for two or three seasons.

Poor drainage produces creeping buttercup, rushes and, on wet acid ground, moss. Acidity produces sheep sorrel and, again, moss. Thatch over 15 mm produces a germination bed at the surface and its indicators are the summer annual grasses rather than broadleaves: crabgrass and goosegrass.

Indicator species mapped to the underlying condition and the correction

Indicator species	Condition reported	Parameter to change
Dandelion, broadleaf plantain, knotgrass	Compaction	Core-aerate 75 mm, 50 to 100 mm spacing
White clover, black medick, speedwell	Low nitrogen	Raise annual N to the species budget
Creeping buttercup, rushes	Poor drainage	French drain or surface swale
Sheep sorrel, sorrel	Acidity	Lime 200 to 250 g per square metre if below pH 5.5
Crabgrass, goosegrass	Thatch over 15 mm	Scarify 5 mm in early autumn, overseed
Daisy, yarrow	Cutting height below the floor	Raise the cut to the species band

Density is the control, and it is a number

A dense lawn is a weed control programme. The measured threshold is around 3,000 grass tillers per square metre: above that the canopy closes, light does not reach the soil surface, and weed seed that germinates dies before it establishes. Below that, weed seed germinates and survives.

The practical check is canopy closure. Look straight down at midday and estimate how much of the view is soil. Under 15 percent is dense; over 25 percent means weed establishment is inevitable regardless of how much herbicide is applied.

Density comes from three parameters: cutting height at the top of the species band, nitrogen at the species budget, and an overseed at the species rate every second or third autumn. A herbicide that removes the weeds from a thin lawn leaves the same thin lawn, and the same seed bank germinates in the following season.

Compaction, which is behind most of them

A screwdriver test is the fastest diagnosis. Push it into the soil where the weeds are densest; if it takes two hands and stops at 50 mm, compaction is the driver and no amount of herbicide will change the underlying problem.

Core aeration at 75 mm depth and 50 to 100 mm spacing, two passes at right angles, breaks the compacted layer and lets grass roots back into the pore space. That is what displaces the taproot species over one to two seasons.

Where the compaction is deeper, at 150 to 200 mm, a standard aerator does not reach it. That needs a deep-tine aerator or a subsoiler pass, and it is worth doing once and then maintaining with annual shallow aeration.

Where chemical control earns its place

Herbicide is a tool for rescuing a lawn that is already above the density threshold, or for spot-treating a small infestation of a species that is spreading aggressively. It is not a substitute for the parameter corrections, and on a thin lawn the result lasts exactly one season.

Apply selective broadleaf herbicide when the weed is actively growing, air temperature is between 15 and 25 degrees Celsius, and there is no rain forecast for 24 hours. Below 10 or above 28 degrees Celsius the product is taken up poorly and the risk of damage to the grass rises. Do not apply to a drought-stressed or newly seeded lawn.

For clover specifically, the correct first response is nitrogen, not herbicide. Clover establishes where nitrogen is low; raise the annual application to the species budget and hold it for two seasons, and the clover thins on its own. Spot-treat what remains.

On a lawn that is to be overseeded in the same season, read the herbicide label for the reseeding interval; most selective broadleaf products require four to six weeks between application and sowing.

Questions that come up on this page

Does clover mean my soil is low in nitrogen?: Yes. White clover competes poorly in a dense, well-fed lawn and dominates in a thin one. Raise the annual nitrogen to the species budget, hold the cutting height at the top of the band, and the clover thins over two seasons without herbicide.
Why do dandelions keep coming back after spraying?: Because the compaction that lets the taproot in has not changed. A dandelion root can regenerate from a 25 mm fragment, so spraying removes the top growth and the root re-shoots. Core aeration and a denser canopy are what end the cycle.
Do I need to treat weeds before overseeding?: Yes, but with the reseeding interval in mind. Most selective broadleaf herbicides require four to six weeks between application and sowing, so treat early in the season you plan to overseed, not the week before.
What is the best time of year to treat broadleaf weeds?: Early autumn, when the weeds are moving carbohydrate down to the roots and the grass is growing hard enough to fill the gaps. Spring treatments work but the lawn is less able to close the gaps afterwards.

Sources

The public reference material the figures on this page were checked against:

Annual nitrogen budget15 g·m⁻²

Irrigation per week20 mm

recomputed on these two numbers · species profiles inside ±15%: 8/12 · operation cards touched: 6/7

Kentucky bluegrass, Turf-type tall fescue, Hybrid bermudagrass (Tifway 419), Perennial ryegrass, Zoysiagrass (Empire), St. Augustinegrass (Floratam), Common bermudagrass (seeded), Centipedegrass

Mowing to a set height, Hollow-tine core aeration, Nitrogen programme with split applications, Overseeding and slit-seeding, Irrigation to a deficit or ET replacement schedule, Scarifying and thatch removal

bench heat, dim to bright: 0 / 4 / 4 / 4 / 0

Adjacent entries

Symptom reading table

Four field symptoms, each read back to the parameter that produced it rather than to a product. The last column is the one number that row turns on, with the threshold drawn on it.

Reading	What you see	Chain of causes	Parameter correction	Field confirmation	Scale
Bare patchesreleasedflag the species on the bench →	Bare patches and thin, worn ground recovery window 3–10 wk	Cutting height has been held below the species floor, thinning the stand from the centre of the lawn outwards until the soil is exposed. Concentrated traffic along a path, at a gate or in front of a goal has worn through the canopy to soil, and the species has no rhizomes to repair it. Drought dormancy has gone past the survival limit, four to six weeks for cool-season turf and six to eight for warm-season, and the crowns have died. A fungal patch disease, large patch on warm-season turf or summer patch on cool-season, has killed the crowns in a ring pattern. Grub or chafer larvae have eaten the roots under the patch, and the turf lifts away from the soil like a carpet when pulled. A spill of fertiliser, petrol, herbicide or a concentrated dog urine patch has killed the leaf and the crown together.	Raise the cutting height to the species band: 25 to 40 mm for Kentucky bluegrass, 30 to 50 for perennial ryegrass, 50 to 70 for tall fescue, 40 to 60 for fine fescue. Scarify or core-aerate the bare area to 75 mm depth so the seed has soil contact rather than a compacted surface. Seed at the species rate: 15 g per square metre of Kentucky bluegrass, 30 of perennial ryegrass, 35 of tall fescue, 20 of fine fescue. Where the area is over 1 square metre, use a blend rather than a single species. Where the species has no rhizomes, which is tall fescue, fine fescue and St. Augustinegrass, the only repair is seed or plugs. There is no parameter change that will fill the patch. For a dog urine patch, water 25 mm immediately and leach the salts below the root zone, then reseed. Do not add nitrogen; the patch is already salt-burned. For grubs, confirm by lifting the turf and finding 10 or more larvae per square metre, then treat; below that threshold the lawn recovers on its own. Replace the traffic. A worn path worn again and again needs a hard surface or a paving strip, not another reseed.	Pull a handful of turf at the edge of the patch. If it lifts like a carpet with no roots attached, the cause is grubs or a root disease; if it resists, the cause is surface wear or drought. Look for a ring pattern. Large patch and summer patch kill in expanding rings with a green centre or a green edge, which wear and drought do not produce. Check the cutting height against the species band; scalping produces a uniform thinning across the whole lawn rather than isolated patches. Dig a 100 mm deep spadeful at the edge of the patch and check for larvae, white fungal mycelium, or a hard compacted layer at 50 mm.	4 wk weeks to close
Mossreleasedflag the species on the bench →	Moss colonising thin or shaded turf recovery window 8–24 wk	The surface stays wet: compacted soil, a thatch layer over 15 mm, or a hollow that collects water keeps the top 20 mm saturated for most of the year. Light has fallen below the compensation point of the grass, usually under four hours of direct sun, so the turf thins and stops competing. Soil pH has fallen below 5.5, which suppresses the grass and the bacteria that decompose thatch while moss tolerates the acidity. The cutting height has been held below the species floor for long enough to thin the stand, opening the surface to colonisation. Nitrogen has been below the species budget for several seasons, or above it, in both cases leaving a stand too weak to close the surface. Soil has been compacted by traffic to the point where infiltration drops below 5 mm an hour and every rain sits on the surface.	Core-aerate to 75 mm depth at 50 to 100 mm spacing, two passes at right angles, to break the compacted layer and restore infiltration. Scarify 5 mm in early autumn where thatch exceeds 15 mm, then overseed at the species rate; a thin stand is what moss is colonising. Raise the cutting height to the top of the species band. In shade that means 60 mm for fine fescue and 70 mm for tall fescue, not 30 mm. Switch the species to creeping red fescue, shade rating 5 of 5, where direct sun is under four hours. Moss tolerates shade; most lawn grasses do not. Apply lime only if a soil test reads below pH 5.5, at 200 to 250 g per square metre on a loam, and retest after 12 months. Do not lime on the assumption that moss means acid. Bring the annual nitrogen to the species budget in a shaded lawn, which is a third less than in full sun: fine fescue 4 to 6 g per square metre, tall fescue 8. Improve drainage where water stands: a French drain, a surface swale, or the removal of a compaction pan at 150 to 200 mm.	Push a screwdriver into the soil. If it takes two hands and stops at 50 mm, compaction is the driver and aeration is the first action. Time how long a 100 mm ring filled with water takes to drain. Under 25 mm an hour is compacted; under 5 mm an hour is severely compacted. Map the sun: note how many hours of direct sun the mossy area receives in midsummer, not in spring. Under four hours, no grass species will win without changing the light. Test the soil pH. Moss tolerates a wide range, so pH is only sometimes the driver and should never be assumed. Read the thatch depth with a knife and ruler; above 15 mm the mat is holding the moisture that moss needs.	pH 5.5 soil pH
Thatch over 15 mmreleasedflag the species on the bench →	Thatch layer 15 mm or thicker recovery window 4–12 wk	Nitrogen has been applied above the species budget for several seasons, producing more lignin-rich stem and stolon tissue than the soil can decompose. Clippings have been bagged for years on a lawn that is now below 10 mm of thatch, removing the nitrogen the microbes need to break the mat down. Soil pH has drifted below 5.5, collapsing the bacterial population and shifting decomposition to slower fungal pathways. The lawn is a species with a thatch tendency of 5 out of 5 and has never been scarified. Irrigation is frequent and shallow, keeping the surface constantly moist and the mat compressed rather than allowing it to dry and fracture.	Scarify 5 mm, in early autumn when soil temperature at 50 mm is between 15 and 21 degrees Celsius, with the tines set to just graze the mat. Overseed the same day at the full species rate, 10 to 15 g per square metre for Kentucky bluegrass, 25 to 35 for perennial ryegrass, 30 to 40 for tall fescue. Topdress 1 to 2 mm of sand-loam matched to the root zone, then water 6 to 10 mm a day for ten days. Cut the annual nitrogen to the species budget: 15 g per square metre for Kentucky bluegrass, 10 for zoysia, 6 for centipedegrass and fine fescues. Raise soil pH into the species band with 200 to 250 g per square metre of lime on a loam, applied in the following autumn and retested after 12 months. Switch to mowing at the top of the species band and mulch the clippings, which returns 1 to 2 g of nitrogen per square metre per year.	Cut a 100 mm square flap of turf with a knife, lift it like a hinge and read the brown fibrous layer between the green leaf bases and the dark soil with a ruler. Do it in three places. Push a screwdriver into the profile; if it stops in the mat before reaching soil, the layer is thick and hydrophobic. Watch a hose test: water beading and running off a dry lawn instead of soaking in is the signature of a hydrophobic thatch layer. Check for the crown being lifted above the soil line by parting the grass with both hands; crowns 15 to 20 mm above soil dry out in two days.	15 mm mat depth
Broadleaf weedsreleasedflag the species on the bench →	Broadleaf weed species as indicators of soil and management conditions recovery window 8–30 wk	Compacted soil where the taproots of dandelion and plantain can penetrate but grass roots cannot, so the weeds have an exclusive hold. Cutting height below the species floor, thinning the canopy and letting light reach the soil surface where weed seed germinates. Soil pH outside the species band, which weakens the grass while the weeds in question tolerate the reading. Nitrogen below the species budget for several seasons, producing an open, pale stand that clover and speedwell colonise readily. Surface moisture that stays high, favouring species such as creeping buttercup and moss-adjacent weeds that indicate poor drainage. A thatch layer over 15 mm that keeps seed in contact with moisture at the surface, which is what crabgrass and goosegrass need to germinate.	Core-aerate to 75 mm depth at 50 to 100 mm spacing wherever dandelion, plantain or knotgrass dominate; the taproot species are the compaction indicators. Raise the cutting height to the species band and hold it for a full season. Density, not herbicide, is what keeps weed seed from establishing. Bring the annual nitrogen to the species budget: 15 g per square metre for Kentucky bluegrass, 12 for tall fescue, 6 for fine fescue. Clover and speedwell indicate a lawn that has been underfed. Correct the soil pH to the species band: 200 to 250 g per square metre of lime on a loam to raise half a unit, applied in early autumn. Scarify 5 mm where thatch exceeds 15 mm and remove the mat, which is the germination bed for summer annual grasses. Where drainage is the driver, indicated by creeping buttercup or rushes, add a French drain or a surface swale before any other measure. Overseed at the species rate in early autumn to raise density. A stand at 80 percent cover suppresses new weed germination; a stand at 50 percent does not. Where chemical control is used, treat only the species present, at the label rate, when the weed is actively growing and air temperature is between 15 and 25 degrees Celsius.	Read the indicator species: dandelion, broadleaf plantain and knotgrass indicate compaction; clover and speedwell indicate low nitrogen; creeping buttercup and rushes indicate poor drainage; sorrel and sheep sorrel indicate acidity. Push a screwdriver into the soil where the weeds are densest. Two hands and a stop at 50 mm confirms compaction. Count the stand: lay a 300 mm square frame in three places and count grass tillers per square metre. Below 3,000 tillers per square metre allows weed establishment. Measure the canopy closure by looking straight down in midday sun: if more than 15 percent of the view is soil, the stand is too open. Soil test for pH and phosphorus; weed composition is a hint, not a measurement.	15 g annual N