Tuesday, 12 October 2010

Why is my grass full of weeds and so patchy?

This has to be one of the most common questions I get asked. I've seen it drive people to all kinds of vices (well not exactly). But I have noticed that in striving for picture perfect lawns people can get quite frustrated as they struggle with weeds taking over the lawn, or patches forming as their lawn becomes sparse.

The answer is usually very simple to diagnose.
Choose a grass that is happy to grow in the shade
Plants are just like us humans. We need the right food, water, rest, space and a pollution-free environment if we want stay healthy. The lack of any of those, causes stress, which makes us prone to disease. And just like diagnosing us humans, if you work out which one or more of those are causing the stress, you've most likely solved the problem.

Follow these steps to isolate the problem:
  1. Water - The most common source of stress on lawns is either too little or too much water. The amount your grass needs depends on many factors. Temperature, wind, soil-type, season all affect the amount of water that your grass consumes. Often the type of weed that's imposing itself on your grass will tell you whether you're giving too much, or too little water. The presence of moss or algae on the soil is a good indicator that there is too much moisture around (they often signal poor drainage). Make sure your irrigation system is correctly adjusted for the seasons. Sandy soils drain very quickly causing the grass to dry out easily. Clay soils become waterlogged, and cause several problems as a result.
  2. Food - Plants have 2 main ways of getting their food - nutrients via the soil, and sugars via sunlight. Lawns almost always love as much sun as they can get. If your lawn is sparse or patchy in the shady areas but looks good in the sunny spots, its most likely due to a lack of light. Thin out the canopy of any trees around the trouble spots by removing some of the branches. Pruning trees right back is almost always the last resort, because they will quite likely grow back thicker than before.
    If light isn't a problem, then you may have a lack of nutrients in your soil. You can get your soil tested quite inexpensively - this will tell you what nutrients are missing and how best to treat your lawn. Generally though, feeding your soil with compost will do wonders for your grass. Compost usually has all the micro- and macro-nutrients your soil needs and will improve the soil over time. Feeding your grass with chemical fertilizers is like feeding your kids nothing but vitamins. It might seem like the same thing as real food, but in the long-term they will have health problems. Organic fertilizers or compost are always best.
  3. Space - Grass needs room to grow - both down and across. If you've had builders on site, make sure they haven't dug a hole in your garden, and buried their rubble, leaving just a shallow layer of soil for your grass to grow in. It sounds ridiculous, but I can't tell you how often I see this done.
    Other short-cuts can also be the problem - if paving or pathways or concrete is too hard to remove, sometimes soil is just used as a cover, and grass is grown over the top. You can usually see the signs during times of drought - a light green weedy patch usually forms over these areas. Thatch (a layer of grass clippings that forms a layer above the soil) can be a problem from time to time, especially if you don't use a grass box when cutting. Diseases and mould can form in this layer, which negatively affects the lawn. Clean out any dead grass cuttings once a year by cutting the grass very short and raking the clippings out.
  4. Rest - If your grass gets a lot of traffic, and it doesn't get enough time to recover properly, bare patches will begin to form. Often, pathways form along the most used areas. Consider formalizing a pathway in these areas, or changing to another type of soil covering i.e. hardy ground-cover, gravel or paving.
  5. Pollution - This can be almost anything that creates a toxic environment for the plants. The most usual suspects are animal urine, soapy water, cement, swimming pool water, fuel or oil from lawnmowers, paint, chemical fertilizers, herbicides and pesticides. If the soil is particularly poisonous, the only route that may be left is to remove the soil and bring in new soil. Often though, water can help leach the offending substance out of the soil. Unfortunately, this only results in the toxins being washed into the groundwater. This may not be a problem with animal urine and some substances that break down easily, but for the most part these substances are causing huge long-term health and environmental problems.
Usually by eliminating one or more of the above factors will dramatically improve the health of your lawn.

Sometimes though, if you are really battling with growing lawn in an area, giving up is actually the best solution of all. As beautiful as a virid green lawn can be, its an addiction that we gardeners have become a slave to - there are very few environmental benefits to a perfect monoculture lawn. Work with nature and plant a mixture of low growing groundcovers instead. Or better still, plant a meadow with wild grasses and flowers.
Like any addiction, only once you stop do you fully appreciate the bountiful benefits.

If you have any questions that I haven't answered about your troublesome lawn, feel free to leave a comment?
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