Why do my cuttings rot instead of rooting?

A cutting has no roots, so it cannot replace water, and no defences at the cut surface, so it is vulnerable to rot. Everything about the technique is a balance between those two: humid enough that the leaves do not dry out, open and airy enough at the base that the stem does not sit wet.

What you'll need

• A sharp clean blade or secateurs
• Gritty free-draining mix — half compost, half perlite or sharp sand
• Small pots
• A clear bag or propagator lid
• Rooting hormone (optional)

Step by step

1. Diagnose which failure you have.Base black, soft, slimy, and the cutting pulls out easily: rot. Tips brown and papery, stem still firm: drying. Leaves yellow and dropping while the stem stays firm: usually too dark, or too long without rooting.
2. Cut square, immediately below a leaf joint.The node concentrates the plant's own rooting hormones and the tissue there is dense and slow to rot. A cut in the middle of a stem section leaves soft pith below ground with little rooting capacity.
3. Strip every leaf that would sit below the compost.A buried leaf rots, and the rot spreads up the stem. Take them off cleanly rather than tearing, which leaves a wound.
4. Reduce the leaves that remain.Two or three at the top, and cut large leaves in half across. Every square centimetre of leaf is water the cutting cannot replace.
5. Take off any flowers or buds.A cutting cannot flower and root at the same time, and it will try to flower. Pinch buds out at the moment you take the cutting.
6. Use a gritty mix, not multipurpose.Roughly half seed compost and half perlite or sharp sand. Rich compost holds water against the stem and feeds the organisms that rot it. Cuttings need air at the base far more than they need nutrition.
7. Insert around the edge of the pot.The compost at the rim drains best and warms fastest. Several cuttings round the edge of one pot is the traditional arrangement for good reason.
8. Water once, then leave the compost only just damp.One thorough watering to settle it, then let it be. The humidity you need is in the air around the leaves, not in the compost around the stem.
9. Cover the leaves, but keep the cover off them.A clear bag held up on four sticks, or a propagator lid. Condensation dripping onto leaves that are touching plastic is a reliable route to rot.
10. Bright shade, never direct sun.Inside a bag in direct sun the temperature rises catastrophically within an hour. North-facing light, or under a bench in a greenhouse.
11. Ventilate briefly every few days.Take the cover off for a few minutes, wipe the condensation off the inside, and put it back. It clears the stagnant air that causes most of the fungal problems.
12. Take more than you need, and take them in the morning.The plant is fullest of water first thing. Carry them straight into a bag or a bucket of water and pot them within minutes — a wilted cutting has already lost.

Tips

• Cleanliness matters more than most people think: a clean blade, clean pots and fresh compost remove most of the rot risk before you start.
• Bottom heat with a cool top is the professional combination — it speeds rooting and reduces the time available for rot.
• If half a pot rots, take the survivors out, repot them into fresh gritty mix and start the humidity again rather than leaving them in contaminated compost.

Common mistakes

• Rooting cuttings in ordinary multipurpose compost — It holds too much water and too many nutrients against a stem with no roots. Half perlite or sharp sand transforms the success rate.
• Cutting in the middle of a stem section — The node is where the rooting capability is. Mid-stem cuttings root far less reliably and rot more.
• Leaving all the leaves on — The cutting loses water it has no means of replacing, and the crowded leaves inside a bag stay wet and rot each other.
• A bag touching the leaves — Water sits where the plastic touches, and that is where rot starts. Four short sticks hold it clear.

If it doesn't work

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