Repotting an Agave: Timing, Gritty Mix and Handling the Spines

When it actually needs doing

Agaves are slow, and they do not mind being snug. A plant that has filled its pot is often a better-looking plant than one swimming in fresh compost, because restricted roots keep the rosette compact. Repot because something is wrong or because the plant has genuinely outgrown the pot, not on a fixed two-year cycle.

Most agaves in pots need moving every three to four years. Signs that the time has come are roots coming out of the drainage holes in quantity, a pot that dries out within a couple of days in summer, a rosette wider than about twice the pot diameter so the whole thing tips over, or compost that has broken down into something dark and water-retentive.

Do it warm and do it dry

The right time is late spring into early summer, once the plant is clearly growing and there are months of warm weather ahead. Roots damaged during repotting need warmth to heal, and a plant repotted as autumn arrives sits with fresh wounds in cooling, damp compost. That is the classic way to lose one.

Let the compost go completely dry for two to three weeks first. Dry compost falls off the roots instead of clinging in a wet lump, you can see what you are doing, and the inevitable small root breaks stay clean and dry instead of taking in water. Never repot a wet agave.

Do not repot in winter, and do not repot a plant that is already soft at the base. A rotting plant needs cutting back and drying, which is a rescue operation, not a repot.

Pot and mix

Go up one size only, an inch or two (2.5 to 5 cm) more diameter than the old pot. A big pot holds a large volume of compost that the roots cannot reach, and that unused compost stays wet for weeks. Weight matters as much as size, because a mature rosette is a sail: terracotta or a glazed pot with a heavy base beats plastic every time, and terracotta also breathes moisture out through its walls.

The mix wants to be at least half mineral. A workable recipe is one part peat-free potting mix to one part coarse grit or pumice, plus a handful of coarse sand. If you can squeeze a fistful of the moist mix and it holds together as a ball, there is not enough grit in it.

Do not put a layer of crocks or gravel in the bottom of the pot. It raises the saturated zone rather than lowering it. One large drainage hole kept clear does more good.

How to repot one without getting hurt

The spines are the practical problem. A mature agave cannot be picked up by the leaves, and it cannot be held against your body. Solve the handling before you start, not halfway through with the plant out of the pot in one hand.

1. Protect yourself first Thick gloves, long sleeves and eye protection. Your face passes close to upward-pointing spines when you lean over a rosette, and the sap irritates skin, so keep bare arms away from any cut surface.
2. Make a handling collar Wrap several sheets of folded newspaper or a piece of thick cardboard round the outside of the rosette and tie it loosely with string. You now have a safe cylinder to hold, and the leaves cannot spring open at you.
3. Free the pot, do not pull the plant Run a long knife round the inside of the pot, then lay the whole thing on its side and slide the pot off. Pulling on the plant tears the root plate away from the stem.
4. Clean up the roots Crumble away the old dry compost by hand. Cut off anything brown, hollow or mushy with clean pruners and leave the firm pale roots alone. Do not wash them.
5. Take offsets while it is out Any pups around the base are easiest to separate now. Cut each one free with a short piece of its own connecting stem and set it aside to dry.
6. Replant at the same depth Put a layer of mix in the new pot, hold the plant so the base of the lowest leaves sits at or just above the final soil surface, and fill around it. Never bury the crown.
7. Firm, top-dress, and stop Tap the pot to settle the mix rather than pressing hard, add an inch (2.5 cm) of gravel on top, and remove the paper collar. Do not water.

The fortnight afterwards

The temptation to water in a freshly repotted plant is strong and it is wrong. Broken root ends need a week or two of dry warmth to callus over. Water them immediately and those open ends are an entry route for rot, which is the commonest reason an agave declines after a repot that otherwise went perfectly.

Keep the plant in bright light but out of the fiercest direct sun for the first week, out of rain, and completely dry. After ten to fourteen days give it one moderate watering, then return to the normal long intervals.

Write the repotting date, the pot size and the mix you used on a label pushed into the pot, and note it in your records. Three years later that label is the only thing that will tell you whether it is due again.