Today something about (re-)planting the big (columnar) cacti and euphorbias.
It’s simple: Plant it in such a manor that it can resist a strong wind without ‘bending over’ ending on the ground. And that you prevent the plant from neck-rot.
Make a hole deep and wide enough; better a bit too deep and too wide. Make a soil mix as described in the contribution about cuttings.
Loosen the soil on the bottom of the hole and mix it with the self-prepared soil.
Top this with a layer of approx. 5 cm self-prepared soil.
Place carefully the plant in the hole and spread the roots. Top the roots with a layer of 10-15 cm of self-prepared soil.
Put large rocks in the hole around the plant with a distance of 5 to 10 cm from the stem. And that their tips stick a little bit above ground-level.
Put the rest of the self-prepared soil in such a way that you compact the soil between plant and rocks. And that you shape a small heep around the stem ending at the outer-side of the rocks. This will let the surplus of rain water drain away from the plant keeping the neck as dry as possible.
This method has the ‘disadvantage’ that you have to plant deeper as they were at the nursery or in the pots. This extra depth means a year (or more) of growth before the plant, above ground-level, is as high again as you bought it.
The big advantage of this general method is, provided you did it right, that the columnar cactus or euphorbia will stand as a rock in the wind.
We learned this method in a natural way in one of our gardens. When this first cactus garden in South Africa was planted almost a 100 years ago Marthinus Malherbe planted all the collumnar cacti and euphorbias that way. During the restoration of this garden we had to take (after 24 years of neglect) almost all succulents out and remove the contaminated soil. Removing the big ones was quite a job for their root-system was covered with huge rocks. But not one columnar cactus or euphorbia ’tipped’ in 90 years despite the heavy winds every now and than.