Wicking beds: a short guide

Wicking beds can be a smart way to water. So how do you make and maintain them - and how do they work?

Water smart: wicking beds have many benefits

There’s lots of enthusiasm for wicking beds, especially to grow vegetables, so what’s the deal with them?

Basically, they’re a garden bed constructed with a water reservoir below the soil that provides a steady supply of water to plants, drawn upwards through “wicking” (technically known as “capillary action”) to the root zone. Watering from below significantly reduces the amount of water needed to grow healthy plants and means you don’t have to water every day. It’s peace of mind if you’re away on short breaks, and labour saving if you’re busy. Typically the reservoir will last a week in summer and several weeks in winter but that varies greatly depending on your climate, soil, weather and what you’re growing. In mid-summer it can mean the difference between crops surviving and thriving; the soil surface also stays dryer than if you’re watering from above, and this can mean fewer weeds germinating and fewer fungal problems.

The reservoir is filled with coarse-grained material such as gravel, pebbles or scoria to add strength to the wicking bed while holding a substantial amount of water. Over this goes a sheet of water-permeable geotextile fabric to stop soil or roots getting into the reservoir, then the layer of potting mix or soil that the plants will grow in. The optimum soil depth is 30-35cm, or a bit more for fruit trees. There’s a vertical inlet pipe from the top to the reservoir for refilling, and an overflow pipe. A dipstick lets you check the reservoir’s water level; let it nearly empty before refilling so the soil is not constantly saturated. You need to completely flush out the reservoir at least twice a year because fertiliser salts build up in the water.

There are plenty of online tutorials showing how to make your own wicking beds, or you can buy kits or complete systems (see waterups.com.au, modbox.com.au, wickingbeds.com.au and vegepod.com.au). Some have frames to support climbing vegies and covers to protect against animals; others have bases with wheels so you can move them around as needed.

Studies have shown wicking beds perform as well or better than precision surface irrigated pots (which is a commercial standard no home gardener will achieve) in terms of water efficiency, crop yield and quality, and labour. Low-tech and scaleable, they’re likely to play an important role in the future for small-scale urban agriculture.

Q&A

Can you repot what I call “supermarket” orchids – the small ones crammed into tiny pots – to hopefully re-flower? It’s a shame to throw them out when the flowers die. Eve Smith, Sydney Moth orchids (Phalaenopsis) are often treated as long-lasting cut flowers but you can re-pot every year or two, after flowering, using a coarse orchid mix and a wider pot with ample drainage holes. They thrive in warmth, high humidity and bright, indirect light. Apply soluble orchid flower fertiliser monthly. A period of cooler night temperatures helps initiate new flowers after a two-month rest period. New flower spikes can sprout from old ones that stay green, but remove them if they go brown.

A blue-flowered flower – I think it’s Commelina – is invading my buffalo lawn, especially with the rain. How can I eliminate it without killing the grass? Laurence Watson, Berry, NSW Selective lawn herbicides safe for buffalo grass are readily available and should treat Commelina cyanea, a native, moisture-loving species. Or try “lawn sand” – equal parts of dry sand, iron sulphate and ammonium sulphate; drop a good pinch on damp weeds and repeat as needed. Beware, it stains.

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for June wins $150 worth of products from Neutrog to nourish your garden.