Seed raising is one of the most rewarding aspects of our hobby. Seeing a plant that you have nurtured from a tiny seedling grow into a flowering plant is something of a joy, although you may have to wait an awfully long time for some species!
The general principles for raising cacti and succulents from seed are the same: a fine, free-draining compost that is not going to compact or shrink too much, and cover the seeds with fine-grade vermiculite unless they are dust-like (which some are) or with compost if they are huge (which very few are).
Germination of cactus seeds is more predictable than that for other succulents, probably because succulent seeds are not as robust and have a limited ‘shelf life’ whereas cactus seed can lay in the desert sands for years before an rain falls.
In 2018 I sowed over 300 packets of cactus seeds and got 86% germination (of at least one seed), compare with 73% germination from 120 packets of succulent seeds. Within each packet of seeds the number germinating can vary from one to all! While most cactus seedlings will survive the winter, it’s trickier with succulents, as I will explain later. Sow your seeds early in the season (if you can) to give them a good head start before the winter.
Cacti that are easy to grow from seed include Astrophytum, Echinopsis, Ferocactus, Gymnocalycium, Stenocactus, Turbinicarpus, and most Mammillaria species. More difficult include Austrocactus, Parodia, Sclerocactus and Strombocactus.
Succulents that are easy (although germination is less reliable) include aloes, agaves, most mesembs, Crassulaceae species (the seed is dust-like), a number of caudiciforms (particularly Cucurbitaceae) and, surprisingly, most stapeliads.
Compost
I use the same compost for succulents as for cacti, in 2018 trying out something I’ve dubbed ‘Quail Mix’, based on recipe from BCSS member, David Quail, which has yielded excellent results (like David, I don’t sterilise it). Here is it:
- 40% sieved John Innes seed compost (although No 1 or even No 2 will do) – use a 5mm sieve
- 30% horticultural sand
- 15% vermiculite
- 15% Biosorb or sieved cat litter (2-3mm sieve)
By the way, you can buy sets of fine sieves online (they are sold for bonsai growers) but you could use a kitchen colander.
Pots
Cactus seeds can be sown in very small pots as they are slow growing and a 2″ pot can happily accommodate up to 30 seedlings. Succulents are likely to grow more quickly but you should be able to prick them out within a few months. The size of the seed will dictate the size of the pot. Use a 3″ pot for opuntias, for example, and an even larger one for whopper seeds of some succulents. If you have only five seeds to plant, a 2″ pot will be fine. Use your judgement.
I put a small amount of gravel in the bottom as it makes the pot a bit heavier and more stable. Fill to within 5mm of the top and press down gently using the bottom of another pot. Don’t compress the compost.
Watering & sowing
Stand the filled pots in a tray of water until you start to see wet patches on the surface of the compost. Take them out and put them on a dry tray to drain for 10 minutes.
If you have the patience, you can place each seed individually on the surface or you can be lazy like me and scatter them randomly so you end up with clumps of seedling that you then have to separate. Very fine seed can only be scattered but do it carefully.
Don’t cover very fine seeds at all. Ones that are 0.5-2mm in diameter can receive a sprinkling of fine-grade vermiculite. Larger seeds I usually press into the surface and sprinkle with vermiculite. Big seeds I just press in and cover with compost.
The bag method
As the name implies, you need some (clear plastic) bags. Label each pot clearly and place each at the bottom of a bag. Self-seal bags (eBay is a good source) are ideal as you can open them up to take a peek (although you can usually see any seedlings through the bag). Alternatively, use the cheapest supermarket plastic bags you can find and seal with the wire ties at the top. Obviously, the bigger the pot, the bigger the bag.
Place the pots in a heated propagator or on a tray on a windowsill in your house and wait for them to germinate. This can begin within five days for some succulents and 7-10 days for cacti, but you need to give them at least two months before deciding whether to continue.
A propagator set to 20-25C will yield quicker germination but most will germinate when the ambient temperature rises anyway.
When cactus seeds germinate you can leave them in their bags for several months; in fact, some growers leave them there until the following spring. I usually allow 3-4 months but with a few fast-growing species (opuntias mostly) I take them out sooner.
The ‘bag method’ does not work as well for most succulents except for initial germination (a seed tray with a clear lid may be better). Left in the bag, succulent seedlings are more prone to damping off and species that grow quickly will stick to the condensation on the inside of the bag.
Keep a careful lookout for germination and when a few have sprouted, undo the top of the bag to let in some air. When they begin to look like they are thriving take them out and put the pot in partial shade. With too much shade some species get leggy; too little and some get frazzled. I hope I’m not putting you off but it’s really down to judgement.
General problems
Damping off is cause by a fungus and kills newly germinated seedling, causing them to topple over. It’s by no means unique to cacti and succulents and is said to be the result of cold, damp conditions.
I don’t have a problem with this so it’s clearly nothing to do with not sterilizing the compost. The lack of ventilation is said to be an issue but with the ‘bag method’ there is absolutely no fresh air. Back in the 1970s you could buy something called Chinosol®, a very old antiseptic no longer available but widely used at the time to prevent damping off. Copper-based fungicides are also banned in the UK. I am not convinced either really helps.
Seedlings are most vulnerable within the first couple of weeks. If you see any seedlings keeling over, remove the pot at once and discard it.
Overgrowth by moss or algae happens sometimes but it takes several weeks to develop and I only get it when no seeds have germinated as germination seems to suppress moss growth. Moss may not prevent late germination but it clearly isn’t helpful to have a tiny seedlings sitting in a forest of bryophytes.
How long to wait?
In general, most cacti and succulents will have germinated in 1-2 months at around 25C. Some species germinate all at once while in others germinate sporadically. You may get some seeds germinating very much later than the rest, even the following season. It depends on the species.
In my experience, the percentage of seed that germinate varies widely: sometimes one or two, other times the whole lot! Succulent seed tends to have lower germination rates.
As mentioned above, after a few months you may start to get moss overgrowth in pots where there has been no germination, in which case you are probably better off calling it a day. I have tried keeping pots of sown seeds until the following year but have rarely ever found further germination. Some cacti are said to need a period of dormancy before they will germinate, including Austrocactus spp, which replicates what happens in the wild then the rains don’t come. If you can, allow any ungerminated pots of seeds to dry out in September and try watering them the following spring.
Pricking out
Leave all cacti (except the fast-growing and larger Opuntia types) until the following spring before planting them on. The miniature cacti should survive the winter but I suggest keep them at 5-10C and occasionally giving a light spray of water.
Some succulents seedlings are tricky to establish as they are very delicate in the first few weeks. This particularly applies to many Crassulaceae where the dust-like seeds produce tiny seedlings. In contrast, some succulent groups grow rapidly and you may need to prick them out after a couple of month. Some may be ready to sell by the end of the season, while a few will even flower in the first year!
Over-wintering
The dilemma with those that are winter-growing succulents in the UK is whether to keep watering them through the winter, which is what I tend do sparingly, even mesembs which have a strict watering regimen as adult plants. The exception is caudiciforms which can be allowed to die back (they probably will anyway). All seedlings need to be kept above 10C over the winter.
Lastly . . .
If you love growing things I would encourage you to have a go at some of the ‘nearly succulents’ you will come across in your search for seeds. There are a number of bromeliad seeds around, such as Hechtia, Puya and Deuterocohnia, and also Southern African bulb seeds, such as Albuca, Tulbaghia, Eucomis and Drimia.
Growing from seed
Propagation from cuttings
Where to buy seeds