Best moss killer for lawns, and the job it does not do

Moss control is the rare lawn product that does exactly what it says and still leaves you with the problem. Ferrous sulfate kills moss reliably and quickly. It has no effect whatsoever on the shade, compaction, drainage or pH that let moss outcompete grass in the first place — so the useful question is not which bag, but which package and what you do in the week after.

The short answer

Which package, and who each is for

What each package treats

1. Moss Control Granules — for a shady section

Scotts publishes 17.50% ferrous sulfate monohydrate, an 18.37 lb bag treating up to 5,000 sq ft, application in winter or spring when moss is actively growing, and best results on a moist lawn with the grass mowed low.

Who it is for: someone with moss through a whole shady section or most of a small lawn. It is the only package here that publishes its active ingredient percentage, which is the figure that makes the rate checkable at all.

Who should skip it: anyone treating patches, and anyone without a spreader — there is no hand-application option on an 18.37 lb bag, and hand-scattering iron produces stripes you will look at for a season. Spreader settings covers calibration when a bag gives a rate and no dial number.

#ad Check the Scotts Moss Control Granules for Lawns, 18.37 lb price on Amazon — how we're funded.

2. MossEx shaker jug — for how moss actually appears

Scotts describes the 4.59 lb shaker jug as being for spot treatments or smaller areas of the yard, applied by hand from the jug with no spreader. It publishes no coverage figure and no active-ingredient percentage for this package.

Who it is for: the common case. Two or three patches, a strip along a fence, or a first attempt before committing to a bag. No spreader needed is what makes it usable on a patch at all.

Who should skip it: anyone with a whole shady section, where it costs far more per square foot than the bag. And anyone who wants to know the rate they are applying, because for this package Scotts does not publish one.

#ad Check the Scotts MossEx Shaker Jug, 4.59 lb price on Amazon — how we're funded.

The part that decides whether it works

Both products are treatments. Moss grows where grass cannot compete, and there are four usual reasons — only some of which you can change.

• Shade. The commonest cause and the hardest to fix. If the shade is permanent, shade-tolerant seed is the real answer: best grass seed for shade ranks what actually survives under a tree.
• Compaction. Fixable, and worth fixing — core aeration relieves it. Best aerators covers the tools and dethatching vs aerating covers which job you actually have.
• Poor drainage. Sometimes fixable, often structural. Moss in a hollow that holds water is telling you about the hollow.
• Low pH. Testable, and the one people assume without checking. A soil test settles it — the soil testing guide has the method and best lawn lime covers correcting it in either direction.

The honest framing, which moss and shady lawns sets out in full: if the cause is deep shade you may be choosing between a moss lawn, a shade-seed lawn and something that is not lawn at all. Iron does not enter into that decision.

What to do in the week after

1. Rake the dead moss out. A mat of dead moss blocks seed-to-soil contact and holds water against the crowns of the grass you want.
2. Look at what is underneath. Bare soil needs seed. Thin grass needs overseeding — how to overseed has the method.
3. Fix one cause. Aerate, test the pH, or raise the mowing height so the grass shades the soil rather than the other way round.
4. Expect to repeat the treatment. If the shade has not changed, the moss has not been told to leave.

What we cannot tell you

How fast either product works. Scotts publishes no time to effect for the bag or the jug, no grass-type exclusions for either, and no coverage figure or active-ingredient percentage for the jug at all — which is why the 1,250 sq ft figure on this page is explicitly our inference from the bag's rate. We have applied neither product and measured no result. Scotts publishes no staining warning, so the caution about concrete is ours, drawn from what iron compounds do rather than from the label. We also hold no non-Scotts moss product with manufacturer-published specifications: a liquid ferric sulfate concentrate exists and is widely sold, but its figures appear only on retailer listings, so it is not ranked here. And no product page will tell you whether your moss problem is shade, compaction, drainage or pH — which is the only thing that decides whether you buy this once or every year.