Although moss is not a weed as such, we have included it, as it probably causes more problems than most turf problems and disorders. This especially true on garden lawns, where the turf is not as intensively managed as with sports turf.
Mosses are primitive plants , with many sources citing them as being the worlds oldest plant specimens. Lacking any kind of root structure, they rely on soil moisture to help them survive and reproduce. Although there are several thousand species, approximately 50 species affect lawns and turf.
Moss is more troublesome during the winter months in the UK. The reason for this are.
The lawn or turf surface is often wetter during the winter.
The day light hours are somewhat shorter, with many days dull and gloomy, often lacking sunlight.
Grass vigour is at its lowest during the winter, as growth is very slow or has stopped altogether.
All of the above contribute to the invasion of moss, but more about that later.
Types of moss
Although there are around 50 species of moss affecting turf, they fall into 3 different types.
Fern like or trailing
These are some of the most common types of mosses in turf. Often found in turf suffering from excessive shade and drainage problems, they have a fern like, almost feathery appearance to them. The two main mosses in this group are Hypnum and Eurhynchium, each producing spores in both spring and autumn.
A symptom of this moss is a spongy lawn, especially if the infestation is severe. They will establish in a wide range of conditions, from acidic to alkaline soils, as long as there is sufficient moisture in the soil.
As with most mosses, the optimum time for control is either spring or autumn.
These mat forming mosses are particularly troublesome in acidic conditions. They form a tight mat of vertical stems, measuring between 1 – 25mm high. They are quite aggressive and will form into large patches if left unchecked
The two mat forming mosses are known as Ceratodon and Byrum. Byrum is the tighter, more dense of the two. Ceratodon is often referred to as a winter moss, as it disappears during the spring, before returning again in the autumn, when conditions are favourable.
Similar to the previous type, upright mosses are more common in dry, acidic lawns and turf. However they are the least troublesome of the 3 types of moss. Known as Poltrichum, they can reach nearly 10cm high and will tolerate a cutting height down to 25mm.
Causes and prevention of Moss
Poor surface drainage
The primary cause of moss is excessive moisture or water retention on the surface of the lawn or turf. The most likely cause for this is soil compaction (especially where there is is high clay content), caused by traffic. When a soil is compacted drainage is impeded and the turf remains wetter for longer periods of time.
Regular aeration is the key to beating soil compaction and improving drainage, thus promoting a firmer, dryer surface. Aeration also encourages deeper rooting grasses, helps thatch breakdown and promotes thicker, healthier turf.
A lack of nutrition
Lawns and turf require essential nutrients to stay in good condition and maintain a healthy coverage of grass. If the soil is suffering from a deficiency in nutrients then grass growth is likely to be thin and weak. A thin and weak sward is an open invitation for moss and weeds to invade.
Ensure the turf receives adequate nutrition with a balanced feed program. A typical program would consist of 2 or 3 Nitrogen bases feeds during the spring and summer months. A high Phosphate and Potash should be applied in the autumn to help the turf maintain good vigour through the winter when moss is more troublesome.
Excessive shade and a lack of sun light
During the winter the days are often gloomy and grey with few days of sunlight and shade becomes more a problem on the lawn. Shade is also caused by other agencies such as trees, shrubs and buildings. Grass requires light to grow and retain good health, where as moss doesn’t and thrives in areas of shade.
Although little can be done about the weather conditions, we can still try and reduce areas where shade is a problem. This can include selective pruning of trees or cutting back shrubs and hedges. This will also improve the flow of air over the lawn, helping maintain a drier surface.
Excessive layer of thatch or organic matter
Thatch is a layer of organic matter that accumulates in the base of the turf or lawn. While a little is beneficial, too much causes problems and the lawn becomes spongy and water retentive. The end result is a weak lawn, giving moss the perfect opportunity to invade.
Thatch can be prevented and kept in check with regular scarification (spring and autumn) and aeration. Scarification physically removes thatch from the lawn and should only be undertaken during periods of good grass growth. Aerating the lawn encourages, soil microbes, these microbes feed on the organic matter, breaking it down and keeping the thatch layer under control.
Incorrect mowing practices
Mowing the turf or a lawn too short can place stress on the grass or scalp the lawn. This leaves the grass looking weak and patchy, perfect for an invasion of moss.
Raise the height of cut on the mower to siut the ground conditions and the management regime. Remember the closer the lawn is mown, the more intensive management program is required. Raise the height on the mower in the autumn, prior to the winter. This help retain a little more grass cover and reduce the stresses placed on the turf in the cold winter months.
Lawns and turf that suffer from constant neglect are more likely to be weak with poor grass coverage. When growth is poor it is vulnerable to a range of problems including moss invasion.
Encourage healthy conditions with good turf care practices. These can include applying adequate nutrition, regular aeration & scarification, irrigating during periods of drought etc. All will promote healthy conditions and a thick, tight sward, that will withstand many turf care problems and disorders.
The most common time of the year for controlling moss is early spring time. There are two main reasons why spring is the preferred time for moss control.
The most frequent time for moss to invade is during the winter, therefore spring time is the obvious time for control.
The grass is starting to grow again following the winter months. If the invasion of moss has been severe, the turf may be left looking thin when it has been treated and removed. In order to restore the lawn back to full health as quickly as possible, growth is required. Don’t be tempted to treat moss too early, it is better to wait for the ground to warm up and for the grass to start growing.
Controlling moss is relatively easy and there are numerous products available.
This is the traditional product used for killing moss and is still a very popular product. It is available as a powdered / fine granular formulation and is applied to the turf or lawn by hand or spreader (preferred method).
Lawn sand contain 3 ingredients, which are sulphate of ammonia, sulphate of iron and sand.
Sulphate of iron – This is the product that controls the moss and is used in a range of lawn care products, as well as lawn sand. It can also be applied to the lawn on its own.
Sulphate of ammonia – This is a nitrogenous fertiliser, which is ideal for spring use, as it works well in lower temperatures. It is great for speeding up recovery, once the dead moss has been removed.
Sand – The sand offers no benefit the the turf, it is simple used as a carrier to bulk up the product, which makes application easier.
Applying lawn sand
For best results and accurate application, lawn sand should be applied through a spreader. many gardeners and turf care professionals prefer to apply it at half rate by doing two passes over the lawn or turf. A typical application rate might be 100g/m2, but can avry bewteen manufacturers, so it is important to read the label prior to application.
If possible cut the lawn three days before application, apply the lawn sand, then leave at least another three days before mowing.
Avoid applying lawn sand in windy conditions, as it very powdery and liable to be blown about.
Apply on dry day when rain is not imminent. If no rain has fallen after 2 days of application, irriagte in thouroughly. Avoid walking on the lawn until the product has been watered in.
Don’t be alarmed if the lawn turns black, as this is quite normal when using products that contain sulphate of iron. It will be mainly the moss turning black as it begins to die.
Approximately 2 weeks after the application the moss should be dead and can be raked or scarified from the lawn. Any repair work can then be carried out to help get the turf back into tip top conditions.
Sulphate of Iron
A versatile product that is primarily used for moss control in lawns and turf. It is often incorporated into various turf care products as a moss killer, but it can in fact be used on its own.
It is very cheap and relatively easy to apply through a hand held or knapsack sprayer. It will also discourage worms and suppresses certain turf grass diseases.
Applying sulphate of iron
The product comes as a powdered formulation, that is mixed with water (it mixes better in warm or hot water) and applied to the through a sprayer.
Ideally mix the iron in a separate container or bucket and pour it into the sprayer. It is important to mix it thoroughly as it has a tendency to block nozzles and filters.
Sulphate of iron can contaminate clothes and concrete pathways, so wear old clothes or overalls and mix away from pathways and drives.
It should be sprayed onto the lawn or turf when the grass is dry, and no watering in is required.
Light treatments of sulphate of iron every 6 – 8 weeks during the winter will help keep moss at bay. It also has a greening effect on the turf without stimulating growth, great for a little added colour during the winter.
There are also other liquid iron products available for controlling moss. Most of the come as a concentrate and are simply mixed with water and applied through a sprayer onto the lawn, similar to the above.
Carfentrazone is a relatively new ingredient used as a moss killer in professional moss killing products, such as ‘Scotts Jewell’ and ‘Pan Glory’. In these products it is mixed with mecoprop-p, so the product doubles up as both a moss and weed killer.
The ideal time for use is between March and September (ideally April or May), when growth is active. Unlike sulpahte of iron, which turns the moss black, carfentrazone turns the moss white when it is dead. It usually takes about 2 weeks for complete control, when the moss can be scarified out of the turf.
A couple of weeks after treatment, the moss should have died and is ready to be removed from the lawn or turf. The dead moss can either be removed using a hand rake or a powered lawn rake or scarifier.
Removing moss with a hand rake is ideal for small, tight lawns where it would be difficult to manouvre a machine. A spring tine rake or purpose made ‘scrake’ are suitable for this task. The great thing about hand removal is that you can concentrate more on areas where the infestation was severe. The obvious draw back is hand removal is not really suitable for large lawns or areas of turf, unless you are looking for a good work out.
Powered scarifier or lawn rake
For larger areas of turf, a powered scarifier is the best option, especially the there is a vast amount of dead moss to remove.