Mosses are plants comparatively simple in structure and function and, with the Liverworts, comprise the Bryophyta family – one of the least complicated groups of the plant kingdom.
Mosses are found in very many situations, for example, on stones, tree trunks and turf. If you have moss on your lawns then it is primarily an indicator that you are not looking after the millions of individual grass plants that make up your lawn.
About 600 species of moss occur naturally in this country, but only a few are common on turf. Distinguishing three types of moss is helpful, as each of the three groups of turf-inhibiting mosses tends to occur under rather different conditions.
Although it is generally assumed that moss infestation in lawns is a direct result of acid, waterlogged and compacted soil conditions, some species favour chalky or alkaline soils. Others can be found on light, sandy soils.
Where moss is a persistent problem, it often indicates some fundamental weakness in the turf and treatment with a moss killer is often only a short-term answer.
From the ‘Causes of Moss Invasion list’, it should be obvious that persistent moss problems are an indication of some fundamental weakness in a turf area. The presence of significant quantities of moss for long periods each year suggests that the turf may be excessively acid, lacking in fertilizer dressings or excessively wet with a small percentage of actual grass content.
Correcting these deficiencies will result in stronger grass growth and the moss then tends to disappear naturally because of the increased competition presented by healthy grasses.
Simple treatment with a moss-killing chemical is, therefore, often not the complete answer to moss trouble. Cultural control should always be considered first. Prevention is always better than cure.
A lawn should have nothing in it except good dense healthy desirable grasses – neither weeds nor moss.
Causes of Moss Invasion
1. A moist turf – poor drainage encourages the fern-like and tufted mosses
2. A soft, spongy sward with a thick fibre layer
3. A very dry soil, e.g. over drains, on mounds and ridges.
Inadequate watering or over-drainage encourages the upright type
4. Bare areas remaining after weeds have died
5. Cutting the grass too low
6. Diseased turf
7. Dry acid soil
8. Low fertility, e.g. deficiencies of plant nutrients
9. In appropriate maintenance
10. Inadequate or poor grass cover and growth
11. Low nutrient status
12. Neglect
13. Over-consolidation of the soil - compaction
14. Poor surface levels which may lead to scalping
15. Shade from trees, hedges and buildings and topography – north facing lawn
16. Turf that is not growing under ideal growing conditions
17. Weak and sparse turf
18. Compaction & over consolidation
19. Prolonged periods of wet weather
20. Time of year – autumn, winter and spring
There are three main groups of Moss
Type 1: Hypnum and Eurhynchium species
Fern-like mosses usually trailing amongst the grass stems. Present in many types of turf but characteristic of moist, rather spongy swards where there is a soft surface mat and a quantity of loose litter. Such mosses are often a problem in turf.
Type 2: Ceratodon purpureus and Bryum species
Tufted or mat-forming mosses that are particularly common on excessively acid soils. Ceratodon purpureus is common and is the so-called "winter moss", as it appears to die in spring when native growth starts, only to reappear in the autumn. Tends to become progressively worse unless checked on lawns.
Type 3: Polytrichum species
Upright variety of moss, most common on dry mounds surrounding golf greens etc. Not normally very troublesome, except occasionally under acid conditions.
Mosses are quite distinct, possessing a simple or branched delicate brown stem, which bears directly, and on its branches, thin green filamentous leaves. The plant is anchored to the soil by means of rhizoids, (root-like structures similar to root hairs on flowering plants). The rhizoids also absorb water and mineral salts that are transported via the stem to the leaves. The leaves are delicate, thin and flat and only one cell thick except at the midrib. Because the leaves are thin, carbon dioxide can enter them more easily, resulting in more efficient use of poor light, but the frailty of the leaves also makes mosses very susceptible to drought.
A few mosses such as Polytrichum have extra rows of cells, making the leaves harder, drought-resistant and more difficult for chemicals to penetrate. Along with broad-leaved weeds, moss is the commonest invader of lawns. It will quickly colonise a lawn if conditions are favourable, preventing the establishment of the turf grasses.
Moss Invasion in Lawns
Moss soon establishes on weak and thin swards where there is a lack of competition from vigorous turf. Most moss killers are palliative – the weed soon returns unless the factors responsible for a thin sward are removed. A strong healthy turf is the best answer to moss prevention.
The invasion of turf grass areas by moss plants seems to be on the increase. Poor surface drainage has always been considered responsible for the invasion or mosses, yet many prestigious arenas have been troubled by the incursion of mosses in spite of their intensive care programmes of scarification, aeration and soil modification and over seeding with new grass seed. Most modern chemical control materials seem to be short lived and repeated applications become necessary.
Perhaps lawn owners are not applying the chemical controls accurately enough for a positive response, or are the chemical controls being applied at the wrong time in the moss plant life cycle? Are the moss plants becoming more resistant to the available chemical controls?
There is one point that does spring to mind – there are two periods of growth each year. The first period is in the spring, and then following the compaction of the soil surfaces during use over the summer. At this time of the year, lawn owners begin cultural operations in earnest, including thorough scarification. If the germinating moss spores are not controlled, prior to scarification, the mosses will spread by vegetative reproduction and produce another crop of spores. These will remain dormant, protected by actively growing turf grasses through any dry spell until the autumnal rains occur. Once again the moss spores will germinate and moss growth will be rapid while the soil is still warm.
Most lawn owners will budget for recurring moss invasion each year; but not for a second crop in that year. Again it is interesting to note that after a very dry summer, moss growth can be seen as soon as the soil becomes moist again.
Control of Moss – Cultural Practices
A whole variety of different causes may be responsible for the establishment of one or more species of moss in quantities detrimental to the turf. These causes and their remedies are listed as follows:
Certain mosses are encouraged by lack of subsoil drainage, a compacted or water-saturated surface, or excessive rolling. Excessive moisture in the surface soil, if only a temporary winter phenomenon, may be relatively unimportant, but if the moss becomes established, the porosity of the surface must be improved by aeration, scarifying and the application of sharp sand, or in some cases Charcoal, Gypsum or Lime.
Soil impoverishment leads to scanty covering of grass and the establishment of quite different moss species. Fertilizer applications – Sulphate of Ammonia at 9 grams to 18 grams per sqm, to which some Ferrous Sulphate or Super-Phosphate, both of which scorch but do not kill moss, may be added – encourage thickening of the sward, something that is easily achieved with regular application of a suitable lawn fertiliser every three months. Timing is important, as the moss also benefits from the addition of plant nutrients, so that fertilizer should be applied at the period of maximum grass growth, preferably in February to October.
Some moss species including the troublesome Polytrichum, as well as tough flat lichens like Peltigera canina, develop on acid, sandy or peaty soils, and must be treated with lime or alkaline fertilizers. Similarly, Pohlia nutans can be controlled to a certain extent by making the soil more alkaline. Conversely, Barbula fallax, which generally occurs on calcareous soils, can be gradually reduced by the judicious use of acidic fertilizers such as Sulphate of Ammonia.
The overall problem is that if lawn owners actually looked after their lawns like the turf grass science books advise, they would not have all the problems with their lawns that escalate with the rapid reduction of quality. This assumes that the quality of the lawn is good when they start the ownership of the area.
The lawn renovation process is to turn the tide on the percentage of moss to grass ratio so that grasses are dominant whereas the moss is not.
Control of Moss – Non Cultural
This works well in the long term only if it is combined with cultural control. Do not plan to kill the moss off if you are not going to over seed the lawn to improve the grass content.
Sometimes moss can be encouraged in the short-term on even the most well managed turf areas and lawns. A particularly wet spell of weather or cold conditions when grass growth is limited can, for example, encourage a temporary outbreak of moss. Under these circumstances treatment of the area with a suitable moss killing chemical is often an adequate answer to the problem although underlying factors that can encourage moss should always be considered.
The traditional chemical for moss control in turf is Sulphate of Iron known as Ferrous Sulphate, applied in the calcined form, with or without Sulphate of Ammonia. It is often the form of moss control in the majority of lawn fertiliser sold in Garden Centres. Sulphate of Iron gives a fast kill and is cheap, but is not long lasting. It is often baulked with a carrier such as kiln dried sand, especially in winter, but is more often used for spring/summer application in Lawn Sand. For example, a mixture of 1 part Sulphate or Iron: 3 parts Sulphate of Ammonia: 10-20 parts carrier (sand or compost). This mixture is used at 140g/m2 (4oz/yd2) and is commonly known as "Lawn Sand". You can also purchase soluble Sulphate of Iron which you mix with water and apply as a foliar spray to the lawn.
It is always the Sulphate of Iron in the lawn treatment that will turn the moss black very quickly and stimulate a rapid greening up of the turf area.
New chemicals are most persistent. One of the most popular is Dichlorophen but the use of this active ingredient has now been withdrawn. It had a rapid effect and which persisted for some time. Phenolic moss killers also have their uses and also help control the weed Speedwell, which is a bonus. Some discolouration of the grass can occur unless the material is carefully applied. It is important that the moss is thoroughly wetted with the control chemical too.
A downloadable .PDF version Moss and Moss Control in Lawns is available here
What/When are the best time's of year to treat Moss.
Reply - Anytime like now when the ground is not frozen, there is some grass grass growth and also moss in the sward. See www.thelawnshop.co.uk and Moss Control for some Soluble Iron to treat it.
Posted by: Pete | January 22, 2012 at 16:35
I put a new lawn in May but it's gradually being eaten up by moss. I've already put down some moss killer but it has returned with vengence and now I wonder if I can put more treatment down at this time of year i.e. in the middle of a mild winter.
Reply - Apply a Soluble Iron to the lawn at the end of January or sooner is weather mild. Overseed the lawn in the spring once you start mowing the lawn. Each 3 months, over seed again, especially if a north facing lawn. There are lots of articles about moss control on this blog to help you and overseeding and grass seed.
Posted by: trgdudley | December 27, 2011 at 22:34
It looks awful. I have scarified it and have now put down a lawn conditioner but there are bare patches every where.
Reply - over seed it with new lawn seed and the bare patches should quickly fill in otherwise they will soon have weeds and moss in these areas.
Posted by: Mississauga Real Estate | November 10, 2011 at 04:51
Good stuff as per usual, thanks. I do hope this kind of thing gets more exposure.
Repy - thanks!
Posted by: | October 31, 2011 at 06:18
Very informative thanks. I will now commence operation bowling green!
Posted by: rick smith | September 18, 2011 at 14:29
Hi what is the best way to over seed after scarification do I put compost down on bare areas thanks.
Reply - Peter, use a drop fertiliser spreader or a rotary spreader but you will have to stay away from the flower borders otherwise the gras seed will get into these. Make sure you apply at least 15 grams per sqm across all of the lawn. You can top dress afterwards to restore the micro levels. Search Blog for Grass Seed, Over Seeding and Top Dressing to find the articles you require to help you. Apply seed as soon as you are able to take advantage of the rain :-)
Posted by: Peter chaloner | June 22, 2011 at 21:24
Hi, I have an infestation in my lawn of some type of ground covering weed, it looks like blanket weed that you'd find in a pond. The usual granular weed and feed doesn't touch it. It is rapidly spreading throughout the whole lawn and seems to smother the grass and ultimately kill it off. Please help!
Reply - pictures are always great - email to sales@lawn.co.uk
Posted by: Rich | June 19, 2011 at 20:06
I have applied a well known 4 in 1 treatment for my lawn two weeks ago. It looks awful. I have scarified it and have now put down a lawn conditioner but there are bare patches every where. Will the grass grow back?
Reply - we bet that is had not rained since it was put down either? Applying a 3 in 1 or 4 in 1 multi roduct can 'shock' a lawn, especially if in drought or semi drought. Always best to apply seperate products. Over seed the lawn once rain promised infact you should always overseed a lawn following scarification. Hope this helps!
Posted by: Caroline Jones | May 23, 2011 at 21:54
I have put lawn weed & feed on my lawn two weeks ago and have just scarified it. I have removed a vast amount of thatch and moss but unfortunately there is a dearth of rain at present. I have been watering the lawn at dawn and dusk, is this the correct procedure.
Reply - Yes. Best to over seed your lawn after scarifying it too. Pray for more rain too!
Posted by: Trevor Prince | May 02, 2011 at 11:49
ive moved in to my house a year ago and now having the time and weather i have used a scratcher machine to pick up the moss from my lawn and applied feed and weed and moss killer to it, will this work?
Reply - always apply lawn treatments at least two weeks ahead of any mechnical work like scarifying. The trick is to kill the moss with Soluble Iron and then after two weeks, scarify it out and then over seed the lawn.
Posted by: andrea | April 22, 2011 at 12:31