Advice for Top Dressing Lawns

Need advice for top dressing lawns? Keep reading to find step by step advice from start to finish.

Top dressing is the process of applying compost, soil, or sand over the surface of your lawn. It has been performed on golf courses since the sport was invented in Scotland, but has only recently become popular on home lawns.

Good soil is living soil. That may sound like a cliche, but it's true. One tablespoon of soil can contain billions of microorganisms. These microscopic organisms are one of the reasons we have plants and trees. In nature, soil microbes enrich soil by converting fallen leaves, limbs and other debris into nutrients plants can use. Since many home lawns have poor quality soil, top dressing becomes even more important. Top dressing is simply a way of adding organic material and restoring the balance to home lawns, building better soil and increasing soil flora.

Below is a list of some of the benefits when topdressing lawns.

  • Top dressing adds organic matter to soils.
  • Top dressing can build up the soil flora.
  • Top dressing combined with core aeration can place organic material deeper into the soil.
  • Organic top dressing can change soil structure.
  • Compost top dressing with the right biological components can help reduce lawn diseases.
  • Adding compost helps reduce traffic stress.
  • Compost incorporated into heavy soils helps relieve compaction problems.
  • Compost incorporated into sandy soils helps with water retention.
  • Top dressing with the right materials can help reduce the need for fertilizer.
  • Top dressing can help reduce thatch.
  • The Cation Exchange Capacity of compost is approximately ten times higher than most loam soils.

A Note About Soil pH

Be sure to correct any soil pH problems before or after top dressing lawns. Here's why.

Bacteria are by far the most abundant form of soil microbes in your soil. Low soil pH, at 5 or lower, will begin to favor fungi over bacteria, including pathogenic fungi. Since beneficial bacteria feed upon many pathogenic fungi and help to keep their numbers in check, it is important you favor bacteria. (Unless your specific plants prefer acidic soil) For additional help, please see our page on Understanding Soil pH. It will also show you how to correct any problems.

Since compost is neutral or slightly alkaline, if your soil pH is slightly low, the compost alone may help to bring it up to where it needs to be.

The Basics for Top dressing lawns 

Choosing the Right Materials

Professionals topdress for different reasons using different materials. Golf green, for example, are most often topdressed with sand.  However, top dressing lawns is better performed using compost. The goal is to build better soil structure and a better environment for macro and microorganisms. Choosing the right compost material is important, since most composts are not equal in nutrient levels.

To lower the cost of the topdressing, some have mixed the compost with topsoil or sand. If you decide to do this, it is very important to match the soil you plan to use with the soil you have in your lawn. Not all soils are compatible.

The rule for sand or sandy/loam soil is: when top dressing lawns, do not spread finer textured sand over a coarse textured soil. Most problems occur for those with sandy/loam soils, when a much finer sand is mixed over a more coarse sandy/loam lawn. The very fine sand can fill the air pockets in the soil ruining the structure. Sand comes in different textures (sizes), so you will need to use the coarsest textured sand. (Fine sand is small grain- Coarse sand is larger grain sand) This will usually be construction grade sand.

In addition, grass types that form thatch will be more problematic than grass types that don’t form thatch. Instead of mixing, the top dressing will frequently form a barrier on the surface. Over time, and with repeated topdressings, you lawn can become layered. These layers can form almost impenetrable barriers that prevent nutrients, insecticides, and even moisture from reaching deeper into the soil. Where this occurs, lawns may require dethatching or heavy core aeration before top dressing is applied.

For those who are seeking an organic lawn care program and will be depending on the nutrients within the compost, it could be especially useful to check the nutrient analysis first. Nutrient levels will vary greatly depending on the materials. If you are not sure what's in it, you can always have it tested. Your university extension office can provide information and instructions on where to send the sample. Some extension offices will even send the sample in for you. There is usually a nominal charge for the test.

There is a lot of talk these days about fertilizers and nitrogen leaching below root depth. The statement below is one of those fun facts most people don't know.

The facts are: Anytime top dressing is applied using compost or even organic fertilizers and the available nutrient content exceeds the nutrient requirements of the turf, the nutrients that are not immediately absorbed into the roots may leach below the root zone. (University of Maryland, Agronomy Department) This is something most people attribute to chemical fertilizers, but the same can occur with any fertilizer or compost. This concern is increased with low fertility turfgrasses and sand-based soils.

So remember, top dressing lawns consisting of low fertility grasses, such as centipedegrass, could be problematic. Centipedegrass doesn't need much fertilizer and grows best in low fertility sites.

The best single time of the year for top dressing lawns is in the fall for cool season grasses and in the spring for warm season grasses. This also allows you to combine other cultural practices, such as overseeding, with the top dressing for the best results.

If you do not plan on overseeding your cool season lawn, you can apply topdressing in early spring, so it starts working as the soil heats up.

Steps for top dressing lawns

When top dressing lawns, there are several important steps that can be done to ensure good results. They are listed in the order they should be performed. Not all these steps need to be done on all grasses, so just eliminate the steps you are not performing.

  • If your lawn has more than ½ inch of thatch, dethatch or core aerate your lawn first. Dethatching will leave a lot of debris on the surface, so you will need to remove it before mowing or top dressing. That can be done in the next step.
  • Mow the lawn as low as possible without stressing the grass too much.
  • Bag or remove all of the grass clippings and dethatching debris, if you haven't already done so.
  • When to use core aeration on the lawn: If you have poor soil, i.e. heavy clay, core aeration is recommended first. Consider removing the cores from the lawn surface. If the soil is not too bad, leave the cores on the grass to break down naturally.
  • Spread top dressing over lawn to a depth of ¼ to ½ inch. It is okay to fill in holes, especially if you have poor soil.
  • Lightly brush the grass with the backside of a rake. The object is to get as much top dressing touching the soil as possible.
  • If you plan on overseeding, do this after the topdressing is down. The reason for doing it after you top dress, is so you don’t bury the seed too deeply.
  • If you overseed, remember to keep the soil moist, but not too wet, until seeds have germinated. Some compost can be too hot for newly germinated plants. Aged compost or compost mixed with good topsoil is better in this situation.

With sufficient moisture, much of the top dressing should work into the soil in as little as a few weeks.

Cultural practices often performed when top dressing lawns

Detailed Descriptions of the Steps Listed Above.

Dethatching

When top dressing lawns, you will gain the best results when it is combined with other cultural practices.

Many lawns develop thatch. Thatch is not soil, but an organic layer consisting of shed roots, grass stems, and other grass debris that develops on the soil surface. Thatch with a thickness up to ½ inch doesn’t pose many problems, but any thicker than that should be removed. Thatch is spongy, dries out quickly, traps pesticides and herbicides and makes a poor growth medium. During prolonged dry spells, excessively dry thatch can become hydrophobic. Hydrophobic thatch is a condition where water pools on the thatch surface instead of being absorbed. Roots can’t tell the difference between thatch and soil and will often grow into the thatch.

If the lawn needs to be dethatched, it is better to do that first before the topdressing goes down. Not all grasses make thatch. Grass types that produce stolons or rhizomes tend to be the ones that produce thatch. Warm season grasses are the most susceptible. Among cool season grasses, Kentucky bluebrass has been known to develop thatch. If thatch problems are severe, dethatching will leave a lot of debris on the grass surface.

There are several types of dethatchers available to homeowners. Power dethatchers can be rented at equipment rental stores. You can purchase an inexpensive, non-motorized dethatcher that you pull behind your mower. They work well and can be weighted down with sand bags or bricks for greater depth.

Core Aeration and Compost

One of the most beneficial things you can do for your lawn is "core aeration". Core aeration relieves soil compaction by removing plugs of soil ¾ inch wide and 2 ½ to 3 inches long. The removal of these plugs allow more water and oxygen to the root zone. Removing these plugs does not hurt the grass. Multiple passes is better than a single pass with the aerator.

Core aeration can be done on warm season grass just as the grass begins growing and on cool season grass in late September through October. Core aerators can be rented at many rental equipment stores. One concern with aerating in spring is to ensure the soil doesn’t dry out too much in the days following aeration. Depending on your soil, you may have some weed growth since the soil has been disturbed and seeds may be brought to the surface.

If your soil is of poor quality, such as high clay content, remove the cores from the grass surface before top dressing. If the soil is loamy, leave the cores on the surface to break down naturally.

When applying compost, spread approximately ¼ inch evenly across the lawn. It is okay to fill in the holes left behind by the aerator. As compost gets down into the soil, it can help change soil structure.

There are now many pull behind compost spreaders on the market. Find the easiest method that works for you. You may find that using a shovel to fling compost in a fan shape may work well. Snow shovel are light and work well if you can handle it. This can be hard work, so make sure you are healthy and are up to the challenge before starting.

With the increased use and interest of compost, there is now equipment made especially for spreading. Prices range from over $100.00 to over $1000.00 for home and landscape models. Motorized models begin at a 1000.00 dollars. However, a number of lawn companies are now specializing in top dressing lawns, but it can be pricey. In larger cities, you may be able to rent a motorized top dressing machine.

Over-Seeding

People have asked about the best time to seed, before top dressing lawns or after. If you are very accurate with spreading the 1/8 to 1/2 inch of compost, you can overseed first. Most people are not that accurate. It is common to have a ¼ inch in one spot and 1 inch or more in another. Most seed should not be covered with more than ¼ inch of soil or it may have difficulty growing. It may be better to spread your seed after top dressing and then lightly comb over the seed using the back of a rake. This will also help move the compost from the grass surface to the soil.

It is okay to fertilize after top dressing. Nutrients from compost are released slowly from microbial activity, so fertilizer could give your grass some immediately available nutrients.


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Did You Know...?
Top Dressing with organic material can add a significant amount of benefits to your lawn.

Organic top dressing can revitalize your soil microorganisms creating healthier plants, while allowing you to use less fertilizer.