Lawn Weed Control and Moss Control on Garden Lawns
Lawn Weed Control
The appearance of a lawn is marred when there aregrowing in it, and many people seem to have considerable trouble in dealing with them.
This is partly because they have not been managing the lawn correctly, with the result that the grass has become weak, and the weeds have been able to establish and spread without much competition. Another reason is that a great many of the weeds onare the kind that can adapt themselves to the existing cultural conditions.
Two Main Classes of Weeds
Lawn weeds can be divided very roughly into two classes:
- the kind of weed with a flat, rosette habit of growth which enables it to escape the mower, such as plantains, daisies, and
- to a lesser extent, docks and dandelions, which under lawn conditions tend to grow flat on the ground; the other, the creeping, trailing type of weed, which roots at each leaf-joint, such as , mouseear chickweed, pearlwort and sea milkwort. This kind of weed often also has very small, and sometimes hairy, leaves which make it unlikely to absorb sufficient hormone weed killer at any one time to kill it completely.
Of course, there are other weeds which do not fit into these two categories, and which have their own, different methods of survival, but this does explain how weeds have adapted themselves to an unnatural environment.
Weed seeds are always liable to be introduced into a lawn by one agency or another, but when new lawns made from seed are infested with weeds it usually indicates that the preparatory work was skimped and in particular that the ground was not allowed to lie fallow long enough to allowto be dealt with thoroughly.
Weed Control Methods
There are various efficient ways of dealing with weeds. If only a few are present, it is a waste to treat the whole lawn with selective weedkiller; indeed, it may not be necessary to do more than dig them out with a two-pronged fork, if they are the rosette, tap-rooting kind, or to spot-treat them with a selective weed-killer (applied either from an aerosol or a puffer pack), or with a special tool which injects weed-killer into and on to the leaves of the weed.
For bad infestations it will be necessary to treat the whole lawn, and here a word or two about the way in which the “hormone’ or selective weedkillers (which only kill certain types of plants) work is necessary. The main thing to remember is that once they have been sprayed on to the plant, they are absorbed through its leaves into the sap, and are then circulated round the plant’s system, reaching every part of it. Hence, they will be more effective if applied when the plant is growing fast, and the sap is at its most active in the late spring and early summer.
This type of weedkiller is a solution of plant hormones, which stimulates the plant cells so that they multiply too rapidly in certain parts of the plant, particularly the growing points at the tips of the shoots, and thus the plant’s metabolism is upset to a fatal extent. Another point to remember is that using as fine a spray as possible, and covering as much of the leaf and shoot surface as feasible, will provide the maximum effect. It is most important not to make up a solution at a greater concentration than is recommended in the manufacturer’s directions.
A lawn made from seed must not be treated with ordinary selective weedkiller for at least three months after germination (there is a special weed-killer for such young grasses), and the same precaution applies to treating a lawn grown from turf.
Selective weedkillers contain chemicals known by such names as 2,4-D, 2,4,5-T, MCPA, mecoprop, dichlorprop, and fenoprop. These will kill or drastically check most weeds found in lawns and some of them are particularly effective against certain weeds. A combination of 2,4-D and 2,4,5-T is particularly good; mecoprop is especially effective against clover and pearlwort. Speedwell is one of the very few which is virtually unaffected, and requires the use of another material. In this case lawnsand might be used or a solution of tar-oil winter wash mixed with water.
Especially useful are the combined selective weedkiller-fertiliser mixtures which do two jobs at once by killing the weeds and feeding the grass at the same time. Where spot treatment can be carried out, it is sometimes better to use the weedkiller known as paraquat, which kills all plants through their green foliage. This, of course, includes grass, so if used it must be very carefully applied to the leaves of the weeds only. One way of doing this is to ‘paint’ the solution on to the plants, and this could be quite useful when dealing with isolated weeds in a newly sown lawn after the first two or three weeks of germination.
I mentioned lawnsand (a mixture of sulphate of ammonia and ferrous sulphate, with sand to act as a carrier) earlier on; this is an old remedy for getting rid of weeds, and still a useful one. It works by burning the top growth of the weeds and turning it black; it may also discolour the grass, but this is only temporary. Best results are obtained if no rain follows its application for 48 hours, but after this it should be watered in. As it contains nitrogen, it has the two-fold merit of feeding the grass as well. It also helps to remove dog lichen, a greyish-black leathery growth which appears on some lawns where the grass is starved.
Another major trouble on lawns can be moss. Although green and soft to walk on, it tends to die away during the summer if the weather is dry, and is easily scratched up by birds and so on during the winter, so that once it has spread all over the lawn and choked out most of the grass, it does not form a very good substitute. Also, weeds tend to spread to mossy areas.
The chief reasons for its invasion are:
- poor drainage and compaction of the surface;
- starvation of the grass; mowing the grass closely;
- deep shade;
- and, occasionally, too acid a soil,
but the last-mentioned is not nearly as common a reason for the presence of moss as is generally thought. On the whole, any environmental factor, particularly poor drainage, which tends to weaken the grass will encourage moss to spread. Unless the fundamental cause is removed or modified, moss will be persistent and, while it may be removed in the first instance by the proprietary moss killers, it will return to those lawns where the growing conditions are not improved.
Lawnsand can be used to burn it out, and can be applied at any time of the year. Mercurised lawnsand can also be used and has a slightly longer-lasting effect in that it kills the spores of the moss from which new moss plants are formed, as well as burning out its top growth. Liquid moss-killers containing anthracene oil (a tar acid) can also be used. But remember to improve the drainage, eliminate compaction of the soil surface, and feed the grass, if you want to prevent moss from returning. This really is the only way to go with regard to moss control.