You have to be brave to try repotting a cactus without at least wearing gloves! Photo: NayaAnn, depositphotos
By Larry Hodgson
How do you repot a ridiculously spiny desert cactus without getting pricked?
Almost any houseplant needs occasional repotting. Either the plant has grown a lot and you need a bigger pot to contain its ever-expanding roots. Or because it has difficulty standing upright and a larger pot with more soil will be able to act as a counterweight to keep prevent it from falling over.
On the surface, the repotting needs of cacti are not so different from those of other plants. In fact, because of their slower growth, cacti actually need less frequent repotting than the average houseplant. Maybe once every 3 or 4 years rather than every 1 or 2 years.
Also, the soil of plants growing indoors tends to become contaminated with excessive mineral salts after several years of watering with hard water or water containing fertilizers. But since we water the cacti less often than other plants, this accumulation occurs less quickly.
Even so, the time eventually comes when you feel the need to repot yours. How should you do it?
Ouch! Those spines Are Nasty!
What really sets cacti apart from the crowd when it comes to repotting is their covering in ferocious spines. How are you to handle a plant as prickly as a cactus without leaving blood on the table? And even if cacti are the most common spiny plants grown in most homes, there are other thorny plants that present the same problem. This is particularly true of other succulents such as euphorbias (Euphorbia spp.) and Madagascar palms (Pachypodium lamerei).
So, although I use the word “cactus” throughout this article, just take for granted that it also applies to any succulent with thorny stems or leaves.
Tools for Handling Prickly Plants
Here are some methods that can make handling prickly plants a bit safer.
Some cacti have slender, short or curved spines that are less likely to penetrate skin and objects. If so, you can then try to handle them wearing thick gloves, such as leather gloves or rose pruning gloves. Give the plant a gentle squeeze at first, then a little harder. You’ll quickly discover if your gloves are capable to handling the job!
Oven mitts may also work . . . but not always. (Mine don’t!) You always have to experiment before actually starting to repot.
In this method, take a section of newspaper, fold it in 4 or 5 and bring both ends together to form a loop. Now place the loop around the stem and squeeze the two ends of the loop against one another at the base of the stem. Staple them together just beyond the stem and you’ll find they form a handy and surprisingly solid plant holder. You can use it to handle the cactus as you wish, without ever having to touch it.
If you don’t have newspaper, a sheet of paper towel can be used in the same way, but for small cacti. Otherwise, you can use a strip of polystyrene sheeting or of leather to handle a larger one.
Of course, you can also lift and handle a cactus with a pair of kitchen tongs . . . but be careful not to squeeze too hard or you could damage the plant. Newspaper is much safer.
Details to Consider Before Repotting a Cactus
1. It’s best to repot a cactus when it is actively growing or soon will be actively growing. That will be sometime between the end of winter (early March) and the very beginning of autumn (September). Avoid repotting it late in the season, after October and especially during the winter. By then, the cactus will be dormant or preparing to go dormant. In that situation, any wounds to the roots, and they are pretty much inevitable during repotting, will not be able to heal. And a wound that remains open can lead to rot that can be fatal to the plant!
2. Water the plant about a week before repotting. That way, the soil will be barely moist at potting time. Just a tad of humidity helps the roots to slip free from the pot without breaking.
3. Many cacti stay small all their lives and never need a bigger pot than the original one. Or maybe yours has reached an interesting size and you don’t want to see it grow any further. But if you move it to a bigger pot, that can stimulate the plant to grow bigger. The goal of repotting, in these two cases, is not to stimulate further growth, but simply to change the contaminated potting soil with fresh soil. In such a case, simply repot in a clean pot of the same size as the previous pot.
4. For the cacti that you want to see continue to grow, repot in a pot 1 to 2 inches (2 or 5 cm) larger than the current pot. Only in the case of a really fast-growing variety would it be worth considering repotting into an even bigger pot. So, for example, a cactus in a 4-in (10-cm) pot could be potted into a 5-in (12-cm) or 6-in (15-cm) pot.
5. Many people prefer clay (terracotta) pots for cacti. That’s because their walls are somewhat permeable and are therefore deemed to “breathe better.” In fact, however, the difference between the air circulation within the root zone inside a clay pot compared to that of a plastic pot is so minor it’s almost undetectable. The real difference is that the pot allows evaporation. That means the soil will be able to dry out more quickly between waterings and that’s always important with cacti and succulents. However, if you want to use a plastic, fiberglass, ceramic or some other impermeable type of pot instead than clay, that’s easy enough to fix: just water a bit less frequently! As a result, the composition of the pot really isn’t a factor of major importance.
On the other hand, clay pots weigh more than plastic pots and this can be useful for large cacti that having trouble standing upright when their pot is too light. Clay, concrete and ceramic pots might be the best for the “big guys.”
6. What is important, however, is that the chosen pot must necessarily have one or more drainage holes to let out any excess water. The belief that a layer of pot shards, gravel or clay pebbles at the bottom of a pot without a drainage hole can help drainage in any way is to just an old garden myth.
7. As for potting soil, there are commercial potting soils for cacti on the market that are generally fairly good to very good quality. Usually, the manufacturer has simply added extra drainage materials to their regular potting mix. Also, modern potting mixes actually drain very well. You’ll likely discover you can use them as is in repotting cacti and obtain great results. Even many cactus experts just use standard potting mix straight from the bag these days! If you want a coarser, heavier soil blend, though, just add about one third coarse sand or bird grit (the latter available at pet stores and agricultural cooperatives) to your favorite commercial potting soil.
Before You Begin
If you want, you can place a sheet of newspaper, a paper towel or a used coffee filter in the bottom of the pot before you start. This “filter” will let any excess water drain out while keeping the potting soil inside the pot.
On the other hand, never put a “drainage layer” of pot shards, gravel, clay pebbles, etc., at the bottom of a pot. Contrary to popular belief, it actually reduces drainage and can lead to rot. Read more on this common garden myth here: Drainage Layer Woes.
Two Different Planting Techniques
There are two techniques for repotting a cactus. Let’s start with the lesser-known “fast-and-easy” method.
Fast and Easy Repotting
Repotting a cactus is easiest if you use the fast-and-easy repotting method, where you use an empty pot to create a mold the shape and size of the plant’s root ball, then simply drop the root ball into the resulting hole. This method applies especially to large, fairly fast-growing plants, such as columnar cacti (Cereus, Cleistocactus, etc.) and candelabra spurges (Euphorbia lactea, E. trigona, etc.), which you repot not so much to change their aged potting soil as to give them more room for root growth and extra weight to hold them upright.
- With this method, in addition to the new pot that is 2 in (5 cm) larger than the old one, you also need to find a pot of the same shape and size as the pot the plant currently grows in.
- Start by placing a filter at the bottom of the new pot as mentioned above.
- Now pour potting soil into the bottom of the pot, enough so that the root ball will be at the same height after transplanting as it was originally.
- Center the smaller pot inside the bigger one, on top of the potting soil.
- Fill in all around the smaller pot with potting soil and tamp it down well.
- Remove the small pot and you will have a perfect mold of the plant’s root ball.
- Unpot the plant using one of the tools described above (gloves, rolled newspaper or tongs).
- Insert the intact root ball into the mold.
- Tamp down the soil a little around the plant so it is held upright.
- Voilà! It’s done!
Here is the “traditional” method for repotting a cactus.
- Start the same way as for fast-and-easy repotting, that is by placing a filter at the bottom of the new pot and adding enough potting mix so that, when you’ve finished, the root ball will be at it’s original level.
- Remove the plant from its pot as explained above.
- With a finger, a pencil, spoon or chopstick, knock as much of the old soil free as possible without damaging the roots. This soil can go into the compost bin.
- Center the plant in the pot and hold it so it remains at the proper height.
- Fill with potting soil. Be careful to work it in and around the roots. Don’t leave any air pockets.
- Firmly tamp the soil down, adding a little more if necessary to bring it to the same height as the root ball.
Sometimes it’s necessary to stake a tall cactus for 2 or 3 months after you transplant, giving the root system time to settle in. By then, they’ll again be strong enough to support the plant’s own weight.
Don’t Water Right Away!
Perhaps the most surprising thing about repotting a cactus or succulent is that it’s best not to water right away. This appears odd to many gardeners, because normally watering is the last step in any planting process. But for these arid-climate plants, it’s best that the soil remains dry for the first 2 weeks. That way, any damaged roots will have time to heal before being exposed to water. If you start to water too soon, there will be a risk of rot setting in.
After repotting, simply return the plant to a suitable location. For most cacti and succulents, that will be in full sun or at least very bright light.
After 2 weeks (even 3 or 4 in the case of very large specimens), start watering again. Resume the usual watering regimen for succulents, that is, watering thoroughly 2 or 3 days after the soil is dry to the touch. (5-7 days later during fall and winter.) You can find more information on the subject in the article 5 Simple Rules for Watering Succulent Houseplants.
And there you go! A cactus well settled in a new pot that will make you proud for many years to come!