Choose water that is low in mineral content
Using pure water that is low in dissolved solids is essential to the health of a Venus flytrap. Tap water in most of the world will not be suitable for Venus flytraps. Using tap water on your Venus flytrap can quickly lead to poor health and death.
The minerals dissolved in tap water, commonly called dissolved solids, are detrimental to the health of your Venus flytrap. Sodium, calcium, alkaline salts, sulfur, chlorine, and magnesium are regularly found in tap water and are lethal to Venus flytraps.
Although it may not be immediately apparent with a few waterings, over time the dissolved solids will begin to build up in the soil. This buildup of minerals can lead to a sickly looking Venus flytrap and eventually death of the plant.
Use distilled water, rainwater, or reverse osmosis water (from an RO system) when watering your carnivorous plants. Tap water may be safe to use if it measures fewer than 50 parts per million (ppm). Measure the total dissolved solids (TDS) with a TDS meter, which can be obtained for around $15.
Although higher levels of TDS, up to 100 ppm or so, can be tolerated. The growing medium should be flushed regularly if the TDS of the water used is over 50 ppm. This can be done by watering several times over a period of several hours or perhaps a day.
Any plants being watered with high TDS water will also benefit from repotting once per year or more frequently.
Keep the soil moist, not soggy for too long
During their active growing season, Venus flytraps should be monitored, especially during hot and dry weather, to ensure that their growing medium does not completely dry out. Ideally, the growing medium should be evenly moist, not soggy or waterlogged.
Therefore, the tray method, described and pictured below, is best used only while Venus flytraps are in direct sunlight in warm weather.
The above photo shows the tray method for watering Venus flytraps. The “tray method” involves setting a pot with drainage holes in a tray of distilled or other pure water. Venus flytraps soil is very good at retaining water. The media (soil) will soak up water from a tray or bowl almost like a sponge.
When plants are in lots of direct sunlight and the weather is warm, the tray method works well. Growers use this method during vacations when they are away and unable to monitor soil moisture levels. However, the tray method is not a good method to use all year long.
Watering during Venus flytrap dormancy
If the Venus flytrap and growing medium can be regularly monitored, it is best to allow the soil to dry until just moist before watering again. Especially avoid keeping Venus flytraps too wet during their dormancy or when the weather is cool or cold.
During dormancy, it is best to allow the growing medium to become almost dry before watering again. Sometimes this means watering only 2-3 times per month during dormancy.
The frequency that Venus flytraps need to be watered depends on the weather, humidity, and the size of the pot. Larger and deeper pots will retain water for a longer period.
A good general rule is to keep Venus flytrap soil “moist, not wet” most of the time. Soil should be kept less moist during dormancy when the air temperature is cool to cold.