GROWING CRASSULA(S), a beginner’s guide.
What are they?
Crassula is a large, diverse and widespread genus of succulent plants with well over 200 different species. There are also many hybrids and cultivars. In nature, the majority of 150 or so mostly grow in the Western and Northern Capes of South Africa winter rainfall areas. Some are also found in the Eastern Cape summer rainfall zone and even a few which may receive rain at any time. They can endure periods of drought, so they can survive on moisture from fog, mist and morning dew. Many enjoy the shade and protection of bushes but may also be found in the open, on plains, in and under cracks in rocks, in grit pans and on mountain tops. Many different ones can often be found growing together and they invariably grow with other succulent plants such as mesembs.
Most Crassulas are perennial but there are also annual ones. They are extremely variable in size and shape. Some are dwarf miniatures, some grow into larger bushes or small trees. A few are monocarpic so die after flowering and some grow from corms and tubers. It's a fascinating group of plants to collect and grow.
How do I grow them?
For the majority, in the spring and autumn with cool or cold nights and warmer days, they are actively and visibly growing, producing new leaves. During the longer days of and summer and cold, dark days of winter they prefer a “resting” or dryer period. So they need water while growing but little or none when resting. Those from the Eastern Cape will need some summer watering so it's interesting to research where they grow. You can then look to find seasonal rainfall information which adds more interest to the hobby.
Water well when you do but be sure to let them dry out between watering and if in doubt, don't water. They are succulent plants so survive drought better than being wet for too long. Use rainwater if you can. They prefer their growing medium and water to be just on the acid side of neutral.
When growing vigorously, Crassulas produce lots of new leaf growth which requires food and minerals. They do appreciate some feeding but how much depends on what growing medium you use. If grown in a grit-soil mix or a commercial compost, they need less additional feed at first because it's already present in the mix. If it's inert like pumice then they will certainly need regular low nitrogen liquid fertiliser. Some growers advocate feeding at the beginning and end of of the growing season, to give them an early boost and then to help them through a dryer period. In general I recommend half strength low-nitrogen liquid fertiliser occasionally in the main growth periods of spring and autumn. One has to be careful and watch the plants. If the growth is too green or too soft then don't feed as much.
Crassulas can be very colourful plants but will remain green and soft if they are fed too much. A common mistake is watering the plants during the heat of summer. It's never an exact science, but generally when night time temperatures are never below 15C – 60F, they shut down and won't take up any water. So the roots may rot which then travels up into the plant and kills it.
Where should I grow them?
Crassulas are quite tolerant and will grow in a greenhouse, on a windowsill or under artificial lighting. They will grow in whatever country you live in, be it in the Northern or Southern Hemisphere, as long as you can provide the conditions they require.
They need good light, especially when growing. If they are grown in natural light some sort of shading is often beneficial in summer. Some growers move their plants outdoors when suitable. They can be damaged by scorch in a just a couple of hours if they get too hot, so if grown indoors, air movement with a fan can help with cooling. In habitat they can tolerate freezing conditions for short periods in winter, but there it invariably warms up during the day. Elsewhere in cultivation, winters can remain cold for long periods so less water will be needed by the plants then. A minimum winter temperature of 3C - 37F will suffice. Anything over 32C - 89F in summer can cause damage, especially with no air movement.
If you have no natural daylight and want to grow them, LED lighting is the way to go, but that's a whole different game of which I have no experience. However, in theory, it should be very successful as both light and temperature can be controlled to provide the necessary conditions.
What do I grow them in?
Growing medium, soil, compost, substrate......all terms for what Crassulas can be grown in. What they grow in best is often the topic of much opinion and debate. Some growers will only use a mineral blend, others prefer a soil and grit mixture. It really depends on what you can find and buy locally or get delivered. Essentially the growing medium just needs to hold water for a short period before drying out, so needs to drain well and not stay wet for days. It's interesting to experiment and see what works best for you and your individual growing conditions.
Most people find standard plastic pots are fine but others prefer ceramic or even fancy ornamental ones. Again it doesn't really matter as long as the container drains freely and the basic growing principles are followed. Whatever type of pot you choose need not be large. I grow my plants in 5cm (2 inch) plastic pots to start with, then only pot on to something larger as required.
Where can I get them?
It's great to visit a nursery to choose plants, but most people buy their plants online these days. This can be risky, as although Crassulas are mostly not as expensive as some other succulents, many sellers are only in it for a quick profit, selling poor quality and often wrongly-named plants. So do some research before buying. Perhaps join one or two Facebook `groups` (e.g. Crassula Collectors) to see where others are buying and ask for advice. Find recommended sellers.
These plants in most cases will grow quickly and easily from leaves and cuttings. Leaves can be carefully removed from the stems and will produce roots and new plants from the heel of the leaf. Some growers plant them immediately into trays or around the sides of pots. Some will leave them on the surface, others will bury the heel. I prefer to leave cuttings in air until roots appear, before planting them. Try different ways to see what works for you.
Not my choice, but some people use “water culture” which can also work. Place a cutting just into or over water and wait for roots to appear before potting up.
Many growers advocate taking cuttings as soon as possible to have spares to experiment with in different conditions (growing medium, location, etc.) to see what does best in your particular environment. Growing a few spare plants will also give you material to share or trade with other growers to increase your collection.
Can I grow them from seed?
Certainly, but Crassula seeds are rarely commercially available. Many growers with the skills and ideal conditions will produce their own seeds by carefully cross-pollinating different plants. Due to the popularity of Crassula hybrids, many growers like to try producing their own.
But assuming you have obtained good seeds, you need to understand a few basics for success. Once again there are many opinions and methods of how best to proceed. Some growers sow in autumn but others have success sowing in spring, so both will work.
The seeds are usually dust-like, so treat them carefully. The same growing medium you use for plants can be used to sow seeds, although some growers prefer to sieve out the mix of larger particles. Some advocate sterilizing soil before sowing but others consider it detrimental. I know many successful growers who microwave the sowing medium on high for 5-10 minutes, letting it cool before sowing.
A variable temperature range of 15-20C (60-70F) during the day to 5-10C (40-50F) at night works well for germination as it mimics what they experience in habitat.
Small pots or trays may be used. Sow the seeds evenly and gently water them from above or let the pots or trays stand in water until the surface is wet. Some growers sow onto a shallow top layer of fine grit. Fine sand is not recommended as it can harden or “cake” when it dries out. If sown onto fine grit, the seeds should be carefully washed down between the particles. This is my preferred method as the grit supports the seedlings as they grow and also inhibits any growth of moss or algae on the surface. The pots and trays will benefit from being covered by either clear plastic or glass, to maintain the humidity. They can also be put inside plastic bags. Whatever is used should then be shaded from the sun. Under the right conditions healthy seeds will usually germinate within a week to ten days. Any cover should then be removed otherwise the tiny green seedlings can rot. They appreciate air moving over them with a small fan and should be kept out of direct sunlight for the first few months.
Keep them growing by lightly watering all the way through their first year. They should be kept moist (but never wet for long periods) and as they increase in size can dry out for a day or so between watering. After this they should be large enough to be treated as adults.
What about bugs and other nasties?
Cultivated Crassula plants can suffer from mealy bugs both above and below soil level. Red spider can also appear and shows as browning of the leaves. Most generally available pesticides will control them. A more persistent pest is Western Flower Thrips. They will feed on new leaf growth, leave ugly brown marks and are not at all easy to kill. Acephate is a good systemic pesticide which controls thrips but is not available in many countries due to its extreme toxicity.
Seedlings may be attacked by Sciara flies, also known as mushroom flies or fungus gnats. They lay their eggs in the soil and the larvae eat the seedlings. A general systemic insecticide, especially Imidacloprid, will usually control them. Another problem for very young seedlings is damping off. This is a fungal disease that usually occurs when the soil is too wet and there is not enough air moving over the seedlings. It can be controlled by using a solution of copper sulphate.
Other fungal problems such as Rust may effect Crassula and prevention is best by regular spraying with a systemic fungicide. It' s not fatal but marks the leaves and once seen, the damage is done.
Other pests and animals which can cause serious damage are slugs, snails, caterpillars, crickets, birds and mice. All of them can appear suddenly and unexpectedly, so need to be considered and kept away at all costs.
I'm ready to give them a go. Any last words of advice?
It's all about experimenting and seeing what works best for you in your conditions.
Remember that all this advice is guidance. Every grower has a different environment and conditions and this will affect how their plants grow, so it's a process, a learning curve.
Everyone has successes and failures along the way, but every success is a joy and assuming you discover why, every failure should help to understand more about Crassula and how you can grow them better.
There is so much more to learn about these fascinating plants. Not only all the different species but the challenge of growing them well and building a varied collection.
For more information I would suggest you take a look at ICN, The International Crassulaceae Network;
The accepted and revered work on the genus is the Crassula “bible” by H. R. Tölken. His 1977 two volume, “Revision of the Genus Crassula in Southern Africa” is a must for any serious student of them. It's often reprinted and inexpensive.
The alternative and later 1985 “Flora of Southern Africa Vol.14 Crassulaceae by H. R. Tölken is also inexpensive and worth having if you can find a used copy.
Crassula, a collectors guide, by G. D. Rowley is a nice coffee table book with lots of information and photos, although there are quite a few mistakes with plant identification. It's been out of print for many years and commands a high price if you can find one.
A classic old book from 1936 is Vera Higgins "Crassulas in Cultivation". It's an easy to read guide, has nice watercolour illustrations and can usually be found reasonably priced online.