Moss – Why is it in my yard?

Yesterday I received this question on our Viette discussion board:

Moss is taking over the yard and choking out the grass.

Moss creeps into the lawn when grass is thin and weak due to unfavorable growing conditions.

Hmmm, this sounds familiar! Much of my lawn is more moss covered than grass covered.

The thing is that moss doesn’t really choke out the grass but rather it slowly creeps in and thrives under conditions that are unfavorable for the growth of most turfgrasses. Chances are that the areas where the moss is growing did not have a healthy, vigorous stand of grass to begin with. I know that’s how it is at my house. Generally moss cannot compete with grass but it can become established in the lawn when the grass is weak and thin due to poor growing conditions.

How can you get rid of moss in the lawn?

There are several products that can be sprayed or spread on the lawn to kill moss but, unless you figure out and fix the environmental conditions that allowed it to become established in the first place, you will be throwing your money away because chances are good that it will just come back.

So what are the conditions that favor the growth of moss?

The simple answer is they grow well under the cultural conditions that are the worst for growing grass – namely shade, low soil fertility, compacted soil, poorly drained soil, acid soil …

The trick to eliminating moss growth in the lawn is to improve the growing conditions for the grass, at which point the grass will easily outcompete the moss.

Improve the soil. The first thing to do is get your soil tested. Unlike turfgrass, mosses grow well in areas of low pH (acid soils) and low soil fertility. A soil test will provide you with information on nutrient availability and the soil pH. The analysis from these tests will often include recommendations for amendments to improve the pH and nutrient content so the soil is perfect for the optimal growth of turfgrasses (and the demise of the mosses).

Moss absorbs water and nutrients through its leaves so it is able to establish in areas with poor soil fertility.

Aerate your lawn. When the soil is compacted, grass doesn’t grow well because nutrients, air, and water cannot penetrate the soil and get to the roots. This doesn’t affect the growth of mosses because they are non-vascular plants that absorb water and nutrients through their leaves; the “roots” function solely to anchor them to the soil. Core aeration reduces soil compaction and encourages the development of a deep healthy root system for the grass. This should always be done when the grass is actively growing so the roots have time to recover. A core aerating machine can be rented for the job.

Improve drainage. Wet soggy soils lack adequate oxygen for the growth of healthy turfgrass. Improper watering practices and/or poor drainage can lead to overly wet soil. When you water your lawn, be sure to water slowly and deeply every 10 days or so unless there is a soaking rain. This will allow the water to seep deeply into the ground and will encourage the formation of a deep root system. Be especially careful not to over water grass that is growing in shade. It doesn’t use as much water and over watering can lead to disease problems.

Core aeration will help improve drainage but sometimes other measures must be taken including the installation of drainage tiles or filling in depressions.

This shady section of my lawn has more moss than grass! Even a shade tolerant grass selection didn't perform well.

Reduce shade on the lawn. Probably the main reason that moss invades our lawns is that the yard is too shady. Most varieties of turfgrass do not grow well in these conditions and when the grass is thin and weak due to inadequate sunlight, that’s when the mosses take hold – they love shade! I know this is why we have so much moss in our yard. The parts of our lawn that are covered with moss are in fairly deep shade.

This is probably one of the hardest conditions to correct. Often the selective removal of a few trees is all that is needed to reduce the amount of shade on the lawn. In my case, since we are surrounded by woods, this would not be practical. Sometimes simply removing some of the lower branches of the trees is enough to increase the sunlight that reaches the grass. Another approach is to thin the tree canopy (but never remove more that 20%-25% of the limbs in any one season). It is usually wise to consult a certified arborist before doing any major tree work.

Of course the other alternative is to renovate and reseed the shady areas of the lawn with a shade tolerant grass seed blend. This works well if the area is not in deep shade. If your problem is deep shade and you can’t increase the sunlight, you’d better just give up on grass and plant a nice shade tolerant ground cover like vinca or pachysandra!

Once you’ve figured out why your grass isn’t growing well,  you can correct the problem and THEN you can take steps to kill or remove the moss. After the moss is gone, you can reseed the area with the confidence that your grass will come in strongly and the moss will be history!

Read more about moss growth in lawns.

Until next time – Happy Gardening and Happy New Year!