Potting is quite an art when it comes to Venus Flytraps – they love to have some room to grow so you don’t want to pot too tightly, but in the summertime the growing medium can dry out too quickly if the growing medium is too airy.
The solution we’ve found is to pack in the bottom 1/3 or so of the growing medium so that it’s tight, and therefore will hold on to water for much longer. The rest of the growing medium can be looser, sort of like the density of a wet sponge, with some bounce to it but firm enough to hold the plant upright.
You’ll want to repot about every 6 months, optimally. You can go longer, but I’ve noticed Flytraps really love a re-pot, and all sorts of things build up in the growing medium over time, so fresh growing medium is very helpful for Venus Flytrap growth and health.
Make sure you use the appropriate growing medium, one that is mineral-free or minimum. If you use peat moss, you can flush minerals out of it by potting up your Flytraps, then running water from the top of the pot through to the bottom and letting it drain out and away. If you do this 3 times or so, you should flush out most minerals.
You can test the mineral content of your growing medium by soaking it in mineral-free water (Distilled, for example) and then then testing it with a TDS (Total Dissolved Solids) meter, which is usually just only $10 or so. Interestingly, the best growing medium we’ve used so far, premium long-fibered New Zealand sphagnum moss, has a high TDS count (ppm), but is perfectly safe for Venus Flytraps. My guess would be that whatever dissolved solid(s) are in it are OK for Flytraps while those in peat moss are not. A good TDS number is going to be between 0-40 ppm.
When you pot/re-pot, make sure the rhizome (the white-ish “bulb”) is underground but no baby traps should be underground. If the plant is shoved down too far into the growing medium it won’t grow well at all. Sort of like Tom Hanks stuffed down in that blanket-hole in The Money Pit, ha.
Make sure your pot has some insulation, thicker plastic pots or fiberglass pots are best. Ceramic, metal, and glass don’t insulate hardly at all, so should be avoided, especially if you’re growing your Flytraps in extreme temperatures.
So, just like humans, Venus Flytraps don’t like to be held too tight, but like a strong foundation, and appreciate a safe insulated home.
Happy flytrapping and potting!