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I have a lot of fairly thick, short moss growing on my lawn. The grass seems to be growing through it and looks healthy, but I still have a carpet of moss. I try raking it, but it's relentless and continues to grow. What can I do about this?

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Good luck. I've aerated, top-dressed, reseeded, gypsumed, raked, used chemicals... with no significant results, except maybe the chemicals (Moss Away), which I'm reluctant to use very often. This is in a shady area with occasional sunlight during the day, with lots of Norway Maple roots. –  Ed Staub Apr 11 '12 at 17:45
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I know it's kind of subjective, but why not just learn to love moss? –  Peter Turner Apr 12 '12 at 17:42
    
I'm new to a moss-loving region. I'm hoping I'll just learn to love it. In the interim, I have been told that occasionally using a dethatching blade on your mower can help. (I will say, a LOT of moss can make for a less usable yard, though...hard to play soccer on a foot of spongey ground) –  DA. May 21 '12 at 4:00
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2 Answers

up vote 2 down vote accepted

Moss loves acid, compacted soil. Ph is merely a measure of H+ ions in the soil. Rain will leach other cations from the soil, such as Ca++, Mg++, and K+ in about that order and with Ca++ being mostly leached. When this happens, H+ takes their places. This produces an acid soil. Also, the presence of Ca++ in abundance in soil will cause the clay particles to flocculate, or draw close together. Having the clay particles close together actually does the opposite of what you'd guess... it makes the soil looser and resistant to compaction.

So the solution to a moss problem is extremely easy. Just add calcium. The Ca++ will displace H+ ions and reduce acidity. The Ca++ will flocculate the soil and reduce compaction. Grass will again want to grow in the area.

Aeration does very little. The soil will fill in the little holes and go right back to its compacted nature since the cause of the compaction has not been addressed, namely, lack of Ca++.

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Are you saying that compacted soils are due to a lack of calcium? –  kevinsky Aug 4 '13 at 10:52
    
thanks, how would you add the calcium? –  Danger Fourpence Aug 4 '13 at 12:47
    
@kevinsky Yes, I am saying compacted soils are due to lack of calcium. If calcium is adequate in the soil, you could drive a truck over your soil and not overly compact it. See cals.arizona.edu/pubs/crops/az1414.ppt if you have powerpoint. If not, see sierravistagrowers.net/growild/sites/default/files/… for a similar presentation. –  Randy Aug 4 '13 at 19:55
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@DangerFourpence You could add calcium in many ways. Lime will add calcium and counteract acidity. Gypsum will add calcium and sulfate (sulfate is also heavily leached by rain). Calcium Nitrate is a water soluble method of adding calcium. CaNO3 is the fastest way to deliver calcium because it readily dissolves in water. –  Randy Aug 4 '13 at 19:59
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From the eBook "The Nature and Properties of Soils" on page 305 we can see that CaO is leached at 98ppm compared to SO3 at 25ppm and MgO at 5ppm. Then on page 307 we see that the annual drainage losses for CaO are 557lbs per acre compared to SO3 at 132lbs and K2O at 86lbs. Calcium is by far the most leached and will be subject to deficiency in any area receiving more than 30 inches of rain annually. If moss grows, it is assumed rainfall is high, soil is acid, and therefore Ca is deficient. –  Randy Aug 4 '13 at 20:20
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Moss cannot compete with grass under ideal conditions for grass. You could cultivate a moss garden. It never needs mowing!

To improve conditions for grass you can do some or all of these:

  • more light: can you cut back any trees or shrubs to let more light in?
  • reduce compaction due to foot traffic or absence of organic matter
    • add a hard path where people walk
    • sow more grass seed and then top dress twice to 1/4" to 1/2" yearly with weed free compost or topsoil
    • aerate the soil: the best method is to physically remove plugs of soil (takes more work than using a hard rake)
  • drainage: does water sit in puddles after a rain? some regrading to let water flow off the turf might help
  • use a hard rake to physically remove the moss before seeding and top dressing
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Doing a soil test is a really good idea. Finding out the pH, % organic matter, and NPK numbers can help you determine what you can do to improve the conditions for growing grass. –  JGurtz Jun 6 '12 at 18:44
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