Grafting joins two cacti into one plant: a rootstock (the bottom, with the roots) and a scion (the top, the plant you actually want to grow). San Pedro is one of the most popular rootstocks in the world because it is vigorous, tolerant of beginners’ mistakes, and quick to heal. A slow-growing collector cactus grafted onto it can grow several times faster than it would on its own roots.
Why graft?
- Speed. Slow species, such as many Astrophytum, Gymnocalycium and Mammillaria, gain size much faster on a strong rootstock.
- Rescue. A cactus with rotting roots can be saved by cutting off the healthy top and grafting it.
- Plants that cannot live alone. The brightly coloured “moon cacti” (Gymnocalycium mihanovichii forms) have almost no chlorophyll and only survive when grafted onto a green rootstock.
When to graft
Graft in late spring to midsummer, when both plants are actively growing and temperatures sit above about 20 °C. Water both plants a few days beforehand so their tissue is firm and full.
What you need
- A healthy, well-rooted San Pedro stock, ideally 2–5 cm thick for small scions
- A scion of similar or slightly smaller diameter
- A very sharp, clean blade (wipe it with alcohol)
- Rubber bands or soft string to hold the graft together
Step by step
- Cut the stock. Slice the top off the San Pedro straight across, a few centimetres above the soil, into fresh green tissue. Then bevel the outer edges slightly so the rim won’t shrink up and push the scion off as it dries.
- Find the vascular ring. On the cut surface you will see a pale ring, the vascular cambium. This is the living “plumbing” that must connect between the two plants.
- Cut the scion. Slice the base of the scion straight across in the same way. Work quickly: the two fresh surfaces should meet within a minute or two, before they start to dry.
- Join them. Place the scion on the stock so the two vascular rings overlap. If the scion is smaller, set it off-centre so its ring crosses the stock’s ring in at least two places. Twist it gently to push out any air.
- Secure it. Loop rubber bands under the pot and over the top of the scion to hold light, even pressure on the joint.
Aftercare
Keep the grafted plant in bright shade, out of rain and direct sun, and do not water from above. Remove the bands after about one to two weeks. A successful graft stays firmly attached, and the scion stays plump and green (or colourful). Within a month or so it should show new growth. If the scion shrivels or lifts off, simply cut both surfaces again and retry. San Pedro stock is forgiving.
Long-term care
Remove any shoots (pups) that sprout from the rootstock below the graft, or they will take energy away from the scion. Otherwise, treat the plant like any other San Pedro: free-draining soil, plenty of light and a dry winter.