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Moss and lichen

Wintertime brings out the cold weather, the dark days and the moss and lichen.

MOSS

Because most grasses fail to thrive in winter, moss is able to establish and dominate a lawn in a relatively short period of time. It loves damp conditions; unlike grass, it does not require a good supply of oxygen in the soil to survive. Thus, waterlogged areas with poor drainage are prone to developing moss. Moss also likes shade, and one example where moss can thrive is the area beneath trees.

Control:
There are several chemicals on the market that will control moss, but it's important to note that these will give only temporary results. Moss is a symptom and not a cause of unhealthy lawns. The best thing to do is to remove the moss and improve your lawn's health to prevent moss from reappearing.

  • Remove moss. Run a rake over the surface of your lawn to remove the moss. This will also remove any thatch (a build-up of old grass) which can form a spongy layer on the lawn's surface and retain water. If the moss is difficult to remove, apply sulphate of iron. Iron compounds kill moss and stimulate grass growth. (Mix it with water in a watering can and apply). The moss will eventually turn black and can then be raked off.
  • Aeration. Simply aerating your lawn with a garden fork may be enough to improve drainage conditions. 
  • Reduce shade. Remove lower branches of trees or shrubs to allow for more sunlight, and when mowing, set your mower at a higher setting. Mowing too closely to the ground will weaken the grass, or may even scalp the surface and leave bare patches, allowing for the moss to take over, particularly if it's in a shady area.
  • Lime. Moss enjoys acidic soil conditions, so a dressing of lime will discourage moss. It won't kill it, but it will encourage better grass growth.
  • Fertilise. And finally, feed your lawn regularly to encourage strong, healthy grass. Use a specially blended fertiliser high in nitrogen and apply in autumn and spring.

LICHEN

When lichen is wet from rain or dew, it grows actively. It also likes sunshine, and will grow well in winter after the leaves have fallen from deciduous trees and no longer block the light, or on trees with badly thinned canopies.

If you have lichen growing on the trunks or branches of your trees or shrubs, don't panic. Lichen will not actually harm your trees. That's because it takes its nourishment from the air rather than from its host. Lichens are often blamed for the decline and death of shrubs and trees because they are commonly found on dead branches and limbs. In actual fact, exposed limbs on damaged plants simply give lichens access to the sun they need for growth with little competition.

Lichen will grow on all sorts of surfaces — rocks, woody debris, soil, fence posts, rusty metal, sand and, of course, tree bark — where they don't have to compete with other plants. They tolerate the most extreme environments, from hot dry places, to the wettest rain forests or arctic conditions.  

Lichens act like sponges, taking in everything that is dissolved in the rainwater. They cannot excrete the elements they absorb from air and rainwater. For this reason, they're an excellent indicator of poor air quality. Lichens will not grow where there are toxic elements of polluted air. So if you have lichen in your backyard, it's got to be a good thing!

Control:
There is no need to do anything, as lichen is not detrimental to the health of your plants. But if you do wish to get rid of it — if it's covering ornamental bark, for example — there are a couple of very simple things you can do. First, you can get a scrubbing brush and water and gently rub off the lichen. Or you could cover the trunk or limb for a while with shade cloth; eventually the lichen will die from a lack of sunshine.

Jane Wrigglesworth

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH
 
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Last updated: June 2, 2004