How Long Does It Take for Grass Clippings to Decompose?

Grass clippings left on your lawn after mowing will decompose in 3–4 weeks on average. Within 1–2 weeks the grass clippings will often no longer be visible, because they will reach the soil level and begin to break down. Grass clippings added to compost will break down fully in 1–3 months. The easiest way to manage grass clippings is to make sure they are spread evenly on the lawn after mowing, so they can decompose and return nutrients to the soil.

How long does it take for grass clippings to decompose?

Is it OK to Leave Grass Clippings on Your Lawn?

Leaving grass clippings on your lawn, also known as “grasscycling,” is one of the best things you can do for your grass. Grass clippings contain essential nutrients that were pulled from the soil for blade growth. As they break down, these nutrients return to the soil. In fact, grass clippings are the equivalent of 4-1-2 fertilizer for your yard. This means grass clippings contain 4% nitrogen, 1% phosphorus, and 2% potassium. These are all nutrients your lawn needs.

  • Leave grass clippings on your lawn for enhanced grass health.
  • Grass clippings will decompose faster in your lawn than anywhere else.
  • Think of grass clippings as fertilizer that return essential nutrients to the soil.
  • Bagging and trashing grass clippings removes nutrients from your yard.
  • Yards where grass clippings are removed and trashed require extra fertilizer to maintain growth.

The practice of disposing of grass clippings consumes time and energy. Plus, it leads to poor lawn health. Grass clippings contain organic matter that the grass extracted from your soil. By throwing lawn clippings away, you’re trashing soil nutrients. You’re robbing yourself, whether the nutrients were there naturally or put there by your own fertilizer applications. If you remove grass clippings you will have to apply more fertilizer to your lawn to maintain healthy growth.

When Should You Trash Grass Clippings?

If your lawn is diseased—such as with brown spot, rust, or fungus—then it is best to throw away grass clippings. This helps remove diseased material and prevents the disease from spreading throughout your lawn. Diseased grass should be thrown away or burned. It is not suitable for compost.

  • Bag and trash grass clippings if your lawn currently has a fungal disease.
  • Do not attempt to use diseased grass clippings in compost. The compost can harbor the disease.
  • If grass clippings are piling up in your yard and smothering grass, spread them evenly or remove them.
  • Excess, healthy grass clippings can be used for compost.

In periods of extreme growth, sometimes mowing can produce excess grass clippings that form clumps in your yard. In most cases, these grass clippings can be raked to spread them evenly and begin decomposition. If the grass clippings are smothering the living grass even after attempts to spread them, remove the excess clippings and dispose of them as lawn waste to keep your lawn healthy.

How Do You Make Grass Clippings Decompose Faster?

Dethatching your lawn will help your grass clippings decompose more quickly. Grass clippings left on your lawn do not cause thatch, but excess thatch slows grass clipping decomposition. Thatch is made up of grass roots, runners, and stems that form a barrier between the growing grass and the soil. When this barrier is more than 1/2 inch (1 cm) thick, it blocks grass clippings from reaching the soil and prevents soil microbes from breaking down the grass clippings.

  • Excess thatch prevents grass clippings from decomposing.
  • If your thatch layer is more than 1/2 inch (1 cm) thick, dethatch to encourage faster grass clipping decomposition.
  • Warm, wet conditions cause grass clippings to break down faster.
  • Water your lawn regularly during the growing season to speed up the grass clipping decomposition process.

Heat and moisture trigger grass clippings to decompose. Although you can’t control the temperature of your yard, you can add water. Watering your lawn deeply twice per week during the growing season not only encourages a healthy lawn, but also causes fresh grass clippings left on the lawn to break down more quickly.

Can You Put Grass Cuttings in Compost?

Grass clippings are excellent compost material. They are considered a nitrogen-rich compost ingredient, which is necessary for compost. In your compost pile you want to achieve a 30-to-1 ratio of carbon ingredients to nitrogen ingredients, by weight. So, for a simple compost pile you will want 30 pounds of fallen leaves for 1 pound of grass clippings.

  • Grass clippings are an excellent nitrogen source for compost.
  • Ideal compost has a 30:1 ratio of carbon sources to nitrogen sources.
  • Use grass clippings sparingly in compost. Because they are a nitrogen-rich ingredient, an excess of grass clippings your compost can release ammonia gas—which has a noxious smell.

Pay close attention to your compost nitrogen ratio and add grass clippings accordingly. If you add too many grass clippings your compost will suffer from nitrogen overload and produce foul-smelling ammonia gas. It’s best to add grass clippings to compost a little at a time. Leave most of the grass clippings on your lawn.

Is it Good to Put Grass Clippings in Your Garden?

Grass clippings make an excellent natural mulch. Plus, it’s free! Simply rake up your grass clippings and lay them 3–4 (7.5–10 cm) inches thick in your garden, as you would with any other mulch. The layer of grass clippings will insulate the ground against extreme heat and cold, help the soil retain moisture, and suppress weeds.

  • Use a 3–4 inch (7.5–10 cm) layer of grass clippings in your garden as mulch.
  • Grass clippings are an effective mulch that protects your plants, stops weeds, and retains soil moisture.
  • Grass clipping mulch will decompose and feed your garden soil with organic matter.
  • Because grass clipping mulch will break down in 2–3 months, plan to add more mulch periodically.

Grass clippings used as mulch will break down rather quickly. In 2–3 months, a 4-inch layer of grass clipping mulch will completely decompose. This is good for your garden because all those nutrients in the grass clippings will be put to work feeding your plants. However, you’ll need to replenish your grass clipping mulch 3–4 times per year.

How Quickly Do Grass Clippings Decompose?

How quickly grass clippings decompose depends on the way the grass clippings are used. Here are the decomposition timelines for grass clippings in different applications:

  • Grass clippings left on the lawn: Full decomposition in 3–4 weeks.
  • Grass clippings in compost: Full decomposition in 1–3 months.
  • 3–4 inch layer of grass clipping mulch: Full decomposition in 2–3 months.

The practice of “grasscycling,” or letting grass clippings fall back onto the lawn as you mow, yields the fastest grass clipping decomposition rate. This is the ideal use for grass clippings because they will break down and fertilize your lawn, fueling future growth. This reduces the need for lawn fertilizer and keeps your lawn healthy. At the same time, it saves you the effort of bagging and trashing grass clippings.

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