There are about 10,000 species of mosses which used to be classified with the Liverworts and Hornworts, but the latter are now in a their own divisions. They are bryophytes which means they do not have a vascular system, having leaves and stems but no roots; attachment to the substrate is by fine colourless or brown hairs called rhizoids. Often the leaves are only one cell thick.
They are a common dweller in the lawn, encouraged by our damp climate. In the woodland garden they form a beautiful carpet and are used extensively in Japanese-style gardens. The 19th century gardener and writer, James Shirley Hibberd, advised that moss was essential for inclusion in the lawn so as not to bruise the elbows when rolling on the grass!
Moss is ever-present as the spores float around in the air, invading the grass sward when the fertility is low and the soil is wet.
Sphagnum moss has very good absorption qualities when dried, and has been used to make nappies, sanitary towels and wound dressings. During the World Wars many tons were shipped to the front after being compressed into cakes, sometimes using the same machinery that made the munitions. It has mild antiseptic properties and these were boosted with garlic juices. There is some evidence that use as a wound dressing may go as far back as the Bronze age.
Bog peat is the dead remains of mosses which have been pickled for thousands of years, but still retain their absorbent properties. This makes peat an ideal growing medium which holds moisture and nutrients that are easily available to plant roots, and despite much research nothing has been found to match it perfectly.
Keep the lawn well fed and don't cut it too short, especially when the growth rate is slow in the winter. Improve the drainage by pricking or spiking. Brushing coarse sand over the surface after spiking helps to keep the new pores open. Scarifying can help to spread the moss if it is growing actively, so it might be best to kill it first. This is done with a chemical treatment like Dichlorophen, a weed-and-feed treatment or Lawn Sand. The latter contains Ferrous Sulphate which can be obtained form hardware shops in powder form and is watered on at a rate of 6g per m². (Make up the mixture on a tray or plastic sheet as any spills will leave a rusty stain on paving).
When the moss is blackened and dead use a spring-tined rake or a mechanical scarifier to remove it. An electric or petrol driven form of the latter can be hired, depending on the size of the job. This will only give temporary removal as the problem will return if the cause is not remedied, ie. relieve compaction, improve drainage and don't cut the grass too short, especially at the end of the season. An autumn feed with a low nitrogen content will also strengthen the grass to help it through the winter.
On flowerbeds a good time to remove it is after a frost which will have lifted it and it is easily gathered from the surface. Maintaining a loose dry mulch with a hoe on open soil, keeps moss away. Any sort of applied mulch will eventually be invaded in shaded moist areas, but the lose surface makes removal quite easy.
Sometimes the moss is accompanied by Dog Lichen which grows as greyish, flattened scales. See also Pearlwort, Liverwort and Blue-green Algae.
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