Repotting carnivorous plants: when, how and in what

Signs that a plant needs repotting

Carnivorous plants are repotted less to give roots room than to renew the soil and reset a plant that has outgrown its space. The sources name these signs:

• The plant has grown into the edge of the pot. Flytraps grow across the pot until they hit the side ^[1], and Sarracenia reach the rim and start growing down ^[3].
• The soil has worn out. In flytraps, salty soil makes the traps on new leaves fail to develop ^[1]. The CPN article adds that roots can die and new traps blacken before opening, and that a plant that will not eat should be repotted as soon as possible ^[5].
• Moss has taken over. In pots of temperate sundews, a dense moss mat can stop plants rooting into the soil or separate from it, and the plants decline ^[4].
• Old growth is choking new growth. Sarracenia rhizomes in the middle of a clump grow over each other and weaken ^[3]; in Mexican butterworts a thick thatch of old leaves eventually keeps new roots from the soil ^[6].
• A salt crust on the surface, a reason to repot butterworts early ^[6].

A crowded root ball is usually not the reason. Flytraps have few roots and do not get root-bound; tall pots are there to keep the plant at the right height above the water, not to make room for roots ^{[7, 8]}.

Do not rush a new plant. The ICPS checklist says to keep a newly bought flytrap in its small pot until it has adjusted and is growing well ^[7], and the New York Botanical Garden says a new flytrap should be fine in its original pot for two years or more ^[9].

How often, and when, by plant

Sarracenia: spring or fall?

Two ICPS pages give different timing, and each states its conditions. The division step-by-step calls just before spring growth the best and only good time, adding that plants divided at other times survive but take much longer to recover ^[3]. The rhizome rot page recommends dividing in late fall, right as plants go dormant, in mild climates such as USDA zones 9 and 10 or in greenhouses, so the cuts can callus over winter before growth starts; in zones 7 and 8, it says to wait until late winter for outdoor plants, after the period of extended freezes ^[16]. The New York Botanical Garden transplants during dormancy and calls winter or early spring best for divisions ^[11].

Repotting a Venus flytrap

The ICPS leaf pullings page walks through a full repotting ^[8]:

1. Unpot the plant with planting forceps.
2. Break off the old part of the rhizome, which rots as the plant grows, and pull some outer leaves down and away whole. Keep these pieces for propagation.
3. Prepare the pot with fresh peat and coarse sand. Never use standard planter mix, which has lime and fertilizer; perlite is risky because it can be salty.
4. Set the soil level so the roots and base of the rhizome sit in the peat and sand, leaving room on top for 1 to 2 cm of pure sand. The author finds this works best, though many growers fill with mix to the top.
5. Plant slightly off center, with the growing point facing the middle of the pot, since the plant keeps growing in that direction.
6. Backfill with sand, spray with water and put the pot straight into its water tray so the peat hydrates.

The CPN article adds two points: feed the plant well and repot a few weeks later, unless it has stopped eating, and do not reuse the old soil ^[5]. Pot choice matters too. The leaf pullings page uses taller, wider pots for plants outside, because they keep the plant at the right height above the water, are less likely to tip over, and buffer the few roots against temperature swings ^[8]. When a newly bought plant does need a bigger pot, the checklist suggests one about 8 cm (3 in) wide and 10 cm (4 in) tall ^[7]. The leaf pieces are covered in leaf pullings, and splitting a clump in dividing a Venus flytrap.

Dividing and repotting Sarracenia

The ICPS division page explains why: Sarracenia like to grow into open soil and make their best pitchers at the edge of a clump ^[3]. Its method in brief ^[3]:

• Use a 50:50 mix of peat with perlite or coarse sand.
• Pull the plant out by its leaves, then work large sections back and forth to find weak points in the old rhizome where it breaks naturally; use shears or a knife only when needed.
• Aim for at least three growth points per division. Single growth points struggle for a year or two.
• Peel off old leaves and remove all brown leaf bases, since that thatch is ideal habitat for mealybugs. Check for soft spots and pests.
• Fill the pot halfway, set the plant at its final height, water, then fill and water again.

The rhizome rot page goes further on cleaning: pull dead leaves off at the base, the way you pull a bract off an artichoke, and cut back dead rhizome until no brown tissue remains, even if the plant gets smaller. It also advises quarantining new plants for a week or two ^[16]. For mature specimen plants the Sarracenia guide recommends pots 16 to 20 cm (6 to 8 in) wide ^[2]. Full steps are in dividing Sarracenia, and rot in rhizome and root rot.

Cold temperate sundews in spring

The ICPS repots these as the hibernacula begin to open ^[4]. Lift the winter buds, clean off moss roughly (it will return from spores anyway), keep the old soil if it is still good, and top the pot up with fresh peat and sand. A shallow layer of sand protects the newly planted buds and discourages fungus gnats and crane flies, whose larvae can devastate a pot of sundews. In fall, the same page suggests pushing hibernacula that sit on stems down into the soil and adding sand around buds on the surface so they do not dry out in winter ^[4]. More sun means less moss, though D. intermedia, D. rotundifolia and D. hybrida do better partly shaded in Sarracenia pots ^[4].

Heliamphora and Cephalotus need extra care

The Heliamphora guide calls division a dangerous time, especially for large plants ^[13]. It suggests foliar feeding the week before and watering well the day before; unpotting the plant on its side and keeping as much soil on the roots as possible; snapping or cutting the rhizome between growth points; and potting divisions without air pockets by adding soil a little at a time and tapping the pot rather than pressing with fingers. Afterward, put water or very dilute fertilizer in adult pitchers, hold off soil fertilizer until the plant is growing again, and bag it for about a month if terrarium humidity is below 85% ^[13]. See Heliamphora.

Cephalotus does best in tall pots. When a plant starts to collapse, the ICPS advice is to unpot it, cut off healthy stems for propagation, remove any rotting or black underground parts and repot what is left in new soil. To prevent trouble, keep all plant parts at least 5 cm above the highest water level the pot may see ^[14]. Crown divisions also thin out dense plants and can give nicely growing new plants in under six months ^[14]. See the Cephalotus profile.

Other groups

• Mexican butterworts are best repotted in winter, when they carry small succulent leaves ^[6].
• Nepenthes in a house need larger pots and a heavier mix than greenhouse plants ^[17]. Rooted cuttings stay in their bag until new growth appears before going into their growing pot ^[18].
• Terrestrial bladderworts keep invading fresh soil, so a common technique is to remove half the soil and plants from a pot and replace it with fresh soil ^[19].

Mistakes the sources warn about

• Repotting a newly bought flytrap before it settles; if it is unavoidable, bag it for a few weeks ^[7].
• Using planter mix, with its lime and fertilizer ^[8]; see soil.
• Dividing Sarracenia into single growth points ^[3].
• Leaving brown leaf thatch, which shelters mealybugs ^[3]; see aphids, mealybugs and scale.
• Dividing Heliamphora in hot weather ^[13].
• Setting Cephalotus too close to the water ^[14].