Why water matters
Water is the most common way to lose a carnivorous plant, and it's rarely the water itself that's the problem. It's what's dissolved in it.
Carnivorous plants evolved in bogs, fens and other wet, open places where the soil holds almost no nitrogen or phosphorus. Plants that could draw extra nutrients from insects had an edge, and over millions of years their leaves gradually became traps. Every trap you see, from a flytrap's jaws to a pitcher or a sundew's sticky tentacles, is a modified leaf, and most produce their own digestive enzymes to break down what they catch. Carnivory evolved this way several separate times, in plant families that aren't closely related. Today carnivorous plants grow wild on every continent except Antarctica, from the tropics to the Arctic.
Growing in such pure, mineral-poor conditions, their roots never developed a way to cope with dissolved mineral salts. That's why water that's fine for a houseplant can slowly kill a Venus flytrap or a sundew.
What's in tap water
The concern isn't chlorine. Municipal chlorine and chloramine cause no real problems for carnivorous plants. The real issue is dissolved mineral salts, mainly calcium and magnesium, along with sodium and chloride. They're dissolved right into the water, so an ordinary filter won't catch them. They build up in the growing media over time, slowly damaging roots that are adapted to low-mineral conditions.
A water softener doesn't remove minerals. It swaps calcium and magnesium for sodium, which is just as harmful to these plants. If your home has a softener, treat that tap water the same as hard water.
How much is too much
Water quality is measured in TDS, total dissolved solids, given in parts per million (ppm). Under 50 ppm is safe for every plant we sell.
Tolerance varies by genus. For Venus flytraps, sundews, butterworts and Heliamphora, treat 50 ppm as the upper limit and aim as low as you can. Sarracenia and Nepenthes are noticeably more tolerant, and many growers run them on tap water up to around 100 ppm.
Whatever you grow, flushing the pot with pure water on occasion is a great way to clear out mineral buildup in the soil and keep the roots happy.
Testing your water
A TDS meter is the standard tool, usually $15 to $25 and sold for aquariums, hydroponics or drinking water. It measures how well your water conducts electricity and converts that into an estimated ppm. It's accurate enough for this, and worth owning if you grow more than a plant or two.
Test straight from the tap or your rain barrel, not from a tray that's been sitting under a plant. Standing water picks up pollen, algae and bits of leaf litter, which raise the reading without meaning there's a mineral problem.
Collect or buy pure water
The simplest route is water that's already pure.
Great if you have a spot on your property for a rain barrel. Keep the collection surface clean and away from overhanging trees. Let the first few minutes of each rainfall run off before collecting, since it rinses dust and debris off the roof.
A handy winter option in most of Canada. Collect clean snow well away from roads and driveways, where road salt ends up, and let it melt indoors.
The easy choice for a plant or two. Boiled water is not the same thing, since boiling leaves the minerals behind, more concentrated than before.
Making your tap water safe
If you'd rather use your own tap, test it first, then filter it if it needs it.
Tap water varies a lot from one town to the next, so the only way to know is to test it. If a TDS meter at your own tap reads under 50 ppm, you can use it as is.
A pitcher-style filter that removes dissolved minerals, not just chlorine, and comes in sizes from small pitchers to larger countertop dispensers. It includes its own TDS meter. The filters wear out faster with hard tap water.
Pushes water through a series of filters and a membrane fine enough to filter out dissolved minerals. The Aquatic Life RO Buddie is a popular, affordable place to start. It connects to a faucet or garden hose with no plumbing, and the 4-stage version adds a DI cartridge that brings hard tap water close to 0 ppm.
Brita and PUR style filters, water softeners, boiling and letting tap water sit overnight don't remove dissolved minerals. A softener actually adds sodium.
Mineral buildup
Tray watering
Plants that sit in a tray of water, which is most of what we sell, are more exposed to mineral buildup than plants watered from the top. As the tray water evaporates, whatever minerals were in it stay behind and concentrate in the media with every refill. That's why water purity matters most for flytraps, Sarracenia, sundews and butterworts.
Best practice is to empty and rinse your trays, or swap them out, every few months or once a growing season, depending on your water and conditions.
Signs of mineral damage
Damage shows up gradually. Minerals travel with the water from the soil up into the leaves. The water evaporates, but the minerals stay behind and are deposited at the leaf tips and edges, so over time those start to die off. The roots take a hit too, turning black, and the whole plant slows down into stunted growth.
Watch for:
- Black leaf tips, including the tip of new growth
- Blackening along the edges of leaves, traps and pitchers
- Less dew on sundews and butterworts, as minerals clog the dew-producing glands over time
- Traps that stop responding
- A white, crusty residue on the surface of the media
- Slow or stunted growth
Fixing a buildup
Flush the pot with pure water. Take it out of its tray, then pour the water through from the top and let it run out the drainage holes, away from the tray. This washes the minerals out of the media instead of concentrating them further. Many growers flush every spring and fall as routine maintenance.
