Carnivorous Plants

Venus flytraps, sundews, and pitcher plants evolved in nutrient-poor bogs where the water contains almost nothing. Their roots are adapted to an environment where total dissolved solids rarely exceed 30 ppm. Tap water in most of the UK, with its calcium and bicarbonate, will kill them. Not slowly, not maybe: mineral-rich water causes root burn, stunts growth, and eventually kills the plant.

The mechanism is straightforward. Carnivorous plants get their nutrients from insects, not from the soil or water. Their root systems are designed to anchor the plant and absorb water, not to filter or regulate mineral uptake. When you water them with hard tap water, the calcium, magnesium, and bicarbonate accumulate in the growing medium (usually sphagnum peat or perlite). The salts build up with each watering cycle because the plant cannot process or expel them. Within weeks, the roots are sitting in a mineral concentration their biology was never designed to handle.

The universal care advice across every carnivorous plant society and nursery is the same: use rainwater, distilled water, or reverse-osmosis water. The International Carnivorous Plant Society recommends water with TDS under 50 ppm. Most experienced growers aim for under 30. Venus flytraps and sundews (Drosera) are the most sensitive; Sarracenia (trumpet pitchers) are somewhat more tolerant; tropical Nepenthes are the most forgiving, but even they do better in low-mineral water. This profile targets a TDS of roughly 15 ppm, which is close to what clean rainwater or a basic RO filter delivers. If The Water Dictionary's tap water lookup tells you your water is 280 mg/L hardness, this profile is telling you why your Venus flytrap is dying.