Dear Sibe,

We have started to get moss on our lawn. When is the best time to remove it and what is the best product for the job? Can you please tell me why this happens, as this is the first year it has appeared.

Thank you,

Lynn

Our Gardening Expert replies:

Hi Lynn,

Moss is a plant that needs a moist atmosphere to thrive so grows in wet shady places and is very common growing around the roots of grass in lawns. If you've only noticed this recently in your lawn it's likely to have been there in the past to some small extent as few lawns in this country will be completely free of moss. Normally it's not a big problem - it's all a matter of the balance between grass growth and moss growth. When your grass is growing well, the moss cannot compete and will be at very low levels.

If you take steps to keep your grass growing vigorously, you will also need to control the moss. There are a number of possible reasons that may hinder this. One is poor soil. If your grass is starved of nutrients then feeding the grass with a nitrogenous plant food as soon as it starts to grow will get the grass growing more vigorously. Another possibility is that the soil is very acid. You need to get a soil testing kit to test the alkalinity of your soil to see if this is the case. Most fine grasses will grow well in slightly acid conditions, but if the soil is too acid, growth will be depleted and moss will benefit. If this is the case you can apply garden lime to bring the soil back to a slightly acid condition.

Another possibility is that the soil has been heavily compacted so the grass roots have difficulty penetrating and lack of air in the soil, again restricting their growth. The same effect would be caused by poor drainage conditions. If this may be the case you need to aerate the lawn - see UKTV Style's practical gardening guide' on Lawn Maintenance for more information.

A common cause of excessive moss growth can be cutting your lawn too short. Your grass should not be cut shorter than 20mm (3/4in). The reason for this is that the grass can be seriously weakened and you get hardly any grass growth and lots of weed and moss become established.

Of course, the opposite is also the case - leaving your grass too long can create the damp shady conditions that moss enjoys. On balance about 25mm (1in) high grass is probably the optimum to aim for, no shorter or longer and with regular cutting when the grass is growing well.

As for products to remove the moss, well there are lots of fancy things around in expensive looking packets, but the basic active ingredient in these is Sulphate of Iron (ferrous sulphate). As well as killing moss this has the effect of making the grass grow a lot greener! You'll find this in different brands of lawn sand which often also include nitrogenous fertilizers to get the grass growing again.

If you belong to an allotment or gardening society which sells garden chemicals in bulk you can obtain these quite cheaply, certainly at a small fraction of the price of packet products. Sulphate of Iron should be applied at the rate of about 1/2oz per sq. yd thoroughly diluted in water. Applying the dry powder will kill the grass and everything else in the lawn! I usually add about 2oz per sq. yd. of Sulphate of Ammonia, again thoroughly diluted. This will encourage grass growth and could be applied once a month throughout the active growing season.

Hope this helps!

Sibe

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