Pro Gardeners Swear by This Greenhouse Self-Watering System That Keeps Seedlings Hydrated – And Removes the Risk of Overwatering

Watering seedlings and young plants in a greenhouse can be daunting. There is one technique I have used that can take some of the fear away, and other gardeners also advocate for it. That is to use capillary matting as a self-watering system for plants.

Using this flexible, absorbent material in a greenhouse offers a fool proof way of efficiently watering plants. There is no fear of plants drying out or being killed by overwatering, as the capillary matting keeps them all consistently moist and healthy. It is suitable for a wide range of plants, including seedlings, and a capillary matting watering system is easy to install.

I found that using capillary matting in the greenhouses I worked in was a stress-free way to keep seedlings, cuttings, and small potted plants healthy and hydrated. Plus, the material is non-toxic and can be used for many years. If you want to find out more, I spoke to other gardeners who also use capillary matting to reveal why it works and how to use it in a greenhouse.

What Is Capillary Matting?

Capillary matting is a soft, highly absorbent material made from eco-friendly or natural materials that can be laid on greenhouse staging or benches. It evenly draws water across the fabric and releases it into trays or pots that gardeners sit on top, and it efficiently keeps plants hydrated without overwatering.

‘Capillary matting is a flexible material, often made from recycled materials, that is ‘bonded’ together much like felt rather than woven or knitted,’ explains Lucie Bradley, gardening and greenhouse expert from Easy Garden Irrigation.

‘As it is specially produced for use by gardeners, it will be non-toxic and be rot and mold proof to help keep your plants free from disease, and allows you to reuse it season after season.’

Capillary watering was originally produced for commercial growers, but home gardeners can now buy a capillary matting roll to install a DIY watering system in their greenhouse. You can get a nine-foot x 25-inch capillary matting roll at Amazon, which can be cut to size to efficiently water plants.

The Benefits of Capillary Matting in a Greenhouse

It has been mentioned that a capillary matting watering system can efficiently provide moisture without overwatering plants, so how does it work?

It acts as a self-watering system; provided the capillary matting remains damp, the pots and trays can absorb water whenever they begin to dry. The soil in the pot absorbs moisture through ‘wicking’, the natural process by which it draws water up against gravity via capillary action to hydrate roots gently and efficiently.

Luke Newnes, a gardener and content creator known as The Pink Gardener who is part of the Hillarys Interior Squad, describes capillary matting as a ‘brilliantly simple’ bit of gardening kit.

‘When you rest plant pots on it, the moisture is pulled into the soil as and when the plants need it. There’s no overwatering, no dry spells… it just quietly keeps everything hydrated,’ he says.

‘For busy gardeners, it’s a real lifesaver. It’ll make you wonder why you didn’t try it sooner.’

Slowly absorbing water through wicking is a gentle way for plants to stay hydrated, and it reduces the risk of roots getting waterlogged and damaged. And capillary matting can efficiently water many plants at one time.

I used capillary matting primarily to keep vegetable and flower seedlings, plant cuttings, and trays of microgreens hydrated in the greenhouses I worked in, as they really benefit from consistent moisture. It offers an efficient way to water seedlings without waterlogging them or damaging young plants by overhead watering.

But the system will work for any young plants in containers, too, provided the pots have drainage holes in the bottom and are filled with a light potting mix.

However, it is not great for all plants. Andrew White from Rhino Greenhouses advises against using capillary matting to water plants that prefer drier roots. He warns: ‘Cacti, succulents or Mediterranean herbs, are generally less suitable unless they’re carefully monitored.’

Luke Newnes

Luke Newnes is also known as The Pink Gardener. He is a new-build gardening specialist and content creator. With a talent for transforming outdoor spaces into stunning sanctuaries, he shares expert gardening tips and inspiration, encouraging others to embrace the beauty of nature. 

How to Install a Capillary Matting Watering System

If you are kitting out a greenhouse and want to include a capillary matting watering system, you need a flat surface, a waterproof liner, and a water reservoir (though you can use capillary matting without a reservoir, and we’ll explain how a bit later on). It can be quick to set up.

Firstly, greenhouse staging or benches need to be level; otherwise, you risk water puddling in lower areas rather than the capillary matting being evenly moist. Lucie Bradley advises covering benches with a ‘thick layer of polythene ' to create a smooth, level surface. A product like this PVC waterproof membrane at Lowe's is ideal to use as a base layer.

A plastic barrier prevents water from damaging benches, especially wooden benches, which can grow mold or fungus when constantly damp. Most importantly, it is a waterproof base liner. Alternatively, you can use a plastic tray as a base, such as these heavy-duty trays at True Leaf Market. The capillary matting roll can be laid out or cut to size to fit the base.

There are several ways you can keep the capillary matting damp. You can have a water reservoir at one end, with a strip of matting extending into it to take up water as the matting dries out.

Lucie says you could use a drip irrigation system to drip water onto the surface. She says: ‘Rather than using one dripper per pot, you can use just a few drippers on the surface of the matting as the water will spread evenly across the matting to ensure even distribution.’

A third option, and the one I used in the past, is to monitor the moisture levels of the capillary matting and use a watering can to hydrate it as required. This does require regular monitoring, as the material will stop wicking altogether if it dries out.

But I found it easy enough to use my hand to assess if there was moisture in the matting, and top it up with a watering can as required. It is important that the capillary matting is thoroughly soaked before you place any pots onto it, as dry matting won’t wick efficiently.

‘Being a flexible material, this is easy to do by simply soaking it in a bucket of water before lifting it out and laying it across the surface of your greenhouse bench,’ reassures Lucie.

Some gardeners cover their capillary matting with perforated plastic to keep it clean and prevent plant roots from growing into the material. Such a perforated plastic still allows water to transfer to the soil, and makes it easier to wipe down any mess rather than wash the matting.

Lucie Bradley

Encouraged to garden since she was old enough to walk, Lucie has been working in the gardening industry for over 28 years. This has meant she has been lucky enough to talk to both amateur and professional gardeners every day of the week and is always learning. She believes you can never know everything about gardening as it constantly evolves.

Proper watering is crucial for healthy seedlings, but so is warmth. This is especially the case with early sowings, where seedlings need the protection of a warm greenhouse to get off to a strong start. You can heat a greenhouse by using fan heaters (such as this portable greenhouse fan heater at Walmart), hot beds, or by insulating as much as possible, such as by applying bubble wrap to the glass.

Keeping the temperature up is important in colder climates, especially considering that the minimum greenhouse temperature for seedlings is around 45°F. If it drops any lower at night, it can damage seedlings.