Conservation Comment: Native sundews and how to grow them

Drosera spatulata potted. Photo / Supplied

Sundews are a variety of carnivorous plants. They are adapted to live in nutrient-poor areas such as alpine environments, peat bogs and clay pans. Sundews are found throughout the world including Asia, Africa, parts of the Americas, and Oceania. They belong to the genus Drosera, meaning “dewy”. There are at least 194 species of Drosera worldwide.

Sundews have modified leaves covered in specialised hairs. The hairs secrete a sticky substance called mucilage. They also produce a sweet smell that is attractive to flies and other insects. The insects land on the plant and stick to the mucilage. Some sundew species will curl and fold over their prey. The insect is digested by the plant and absorbed via the hairs, and nutrients such as nitrogen and phosphorus are extracted, helping the plant to grow.

Species found in New Zealand include Drosera arcturi, D. articulata, D. binata, D. peltate, D. pygmaea, D. spatulata, and D. stenopetala. D. stenopetala is the only one of these that is endemic. Others have a wider distribution, for example D. spatulata is found from southern Japan all the way to southern Aotearoa.

There are also two species that have been introduced into the wild in New Zealand. D. capensis or cape sundew is a native of South Africa that was introduced as an ornamental plant. It is known from only two sites in Auckland and the New Zealand Plant Conservation Network suggests to notify the regional council if it is found in the wild. It occasionally grows as a weed in boggy areas and may piggyback in pots with other houseplants. D. neocaledonica is endemic to New Caledonia and is also a coveted specimen for plant collectors.

Sundews can be grown as attractive and interesting houseplants. Some species such as D. spatulata are suitable for beginner houseplant or carnivorous plant enthusiasts. Most sundew species like high light levels so are best placed on a windowsill or under a growing lamp. Sundews can be planted into a mixture of perlite (a pH-neutral substance made from expanded volcanic glass) and peat moss, in about a 50-50 ratio. You can also use pumice, silica sand and sphagnum moss as the substrate. Never use fertiliser when growing sundews because they have evolved in nutrient-poor areas and cannot tolerate the nutrient levels in fertiliser.

Because they are also sensitive to minerals and pH levels in water, they should be watered with only rainwater, reverse osmosis water or distilled water. They should be potted in plastic or glazed pots, not unglazed ceramics, because minerals may leach from the pottery. D. spatulata is a small plant that would only reach the size of your palm. D. binata can grow up to a metre tall. You will need to feed your sundews insects so they can obtain the required nutrition. You can feed them fruit flies or other small flies once every few weeks. You will need to place the insect onto the sticky mucilage and the plant will do the rest.