How to use solarisation to remove weeds from your garden cheaply and effectively

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If you've got a big patch of weeds in a flat spot, you're in luck because there's a chemical-free solution that actually gets the job done. The water and sunlight combination effectively kills them and other soil diseases.

Here’s what you need to know.

What is solarisation?

Solarising in gardening is a method where you use the sun's heat to kill weeds or unwanted ground cover by laying down sheets of plastic to trap warmth in the soil. The main gear you'll need are black or clear plastic and something solid to secure it in place, such as rocks, soil, bricks or metal. Over time, heat from the sun will build up under the plastic, effectively treating the area without the need for pesticides or excavation.

You can also use solarisation to boost your overall soil quality, as heating the topsoil can also kill off pests and diseases.

6. Check for remaining weeds: If some weeds still remain, repeat the process to ensure the area is weed-free.

First off, remember that solarisation works best in areas that get full sun for most of the day. You can give it a go in a spot that gets partial sunshine, but you'll need to give it a bit more time for the process to take effect.

Once you've chosen your patch, follow these step-by-step instructions on getting rid of weeds using the solarising method.

1. Clear the area

Take out as many existing weeds, rocks and other debris as you can from your chosen spot. The solarisation process works best on cleared soil, but if there's still weeds there, you'll need to factor that into how long you leave the plastic in place.

2. Water the soil

Give the soil a good soaking to make sure it's nice and damp. This helps the soil conduct heat better and makes solarisation more effective.

3. Cover the soil

Cover the damp soil with a thick, black or transparent plastic sheet. Use a heavy-duty plastic that's resistant to the sun's UV rays to soak up as much heat as possible. Make sure the plastic completely covers the soil without any holes or gaps.

4. Secure the edges

Dig the edges of the plastic sheeting into the soil or use rocks to hold it firmly in place. This stops heat from escaping and creates a greenhouse effect under the plastic.

5. Leave to cook

Allow the plastic to stay in place for a long time, ideally 4 to 6 weeks during the hottest part of summer. This helps to get the soil temperature up enough to kill off weeds, seeds, and diseases.

In 2024, it was discovered that sunlight had a greater effect on soil temperatures than the surrounding temperature, with the assistant stating "soil solarisation can be planned around sunlight forecasts (e.g. UV index) rather than temperature forecasts."

Remove the plastic

After the solarisation period, carefully take off the plastic. Be careful of any trapped heat or steam. Remove any dead weeds or other rubbish and let the soil cool and dry out before planting.

4. "Pull weeds regularly" – Regularly

When weeds start to take over your garden, it's best to think about stopping them before they get out of hand. After you've put seeds or plants into the soil, there are a few things you can do to prevent weeds from growing back.

Add a weed barrier

Before building or renovating, check for pests that it may attract, such as termites, first.

Add a layer of organic matter to the soil.

It's a top way to stop weeds from sprouting. Apply a layer (about 5-10cm thick), and let it do its thing, stopping weeds in their tracks in your backyard.

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