How to Grow Cacti From Seed

If you’ve got the patience, growing cacti from seed is extremely rewarding

It’s often much easier to find and procure seeds than it is to find adult plants of rare species, and far more cost effective.

It can also be fun to pollinate your plants yourself, creating new hybrids or crossing existing hybrids to create new flower colors and types. 

I’ve come to learn that almost all cacti can be sown in much the same way, although I’ll preface this resource page with the warning that I have not grown every single species on planet Earth myself. There may be some species that don’t respond as well to these methods, or they may not work exactly this well for you compared to my own growing conditions. That’s okay! 

When it comes to learning to grow cactus from seed, I highly recommend picking up some cheap, easy to grow seeds (Astrophytum capricorne or Astrophytum myriostigma are particularly forgiving) and experiment until you find what works for you. What I detail below is what works for me, and I sow at least 1000 seeds each year! 

I’ve been trying to grow cacti and succulents from seed since 2018, and have tried many techniques to find what I do now that works best in my situation. Over the last few years, I’ve finally dialed in my technique well enough to consistently grow seedlings and raise them to a size large enough to sell. 

cactus soil

First: the dirt for your seeds

You don’t need to overthink this too much. Prepare your soil much like you would for a normal cactus mix, but leave some room at the top of the pot.

I use the same ingredients for my seedlings as I do for my older plants, but in a slightly different ratio: 

I mix this up, then fill in the pots with room at the top. It should seem too big and chunky for seeds, and you’re right! If you left it just this way, you’d get really uneven seed distribution. For seed sowing, I add a thin layer of rich houseplant soil to the top of this mix. Just enough to even out the surface, and it gives the seeds an early boost of nutrients to help them gain size quickly. 

Sterilize Your Soil!

Next, before you start adding seeds to the soil, you need to sterilize it! It’s hard to make out in the photo above, but I have all of my pots arranged in a plastic nursery tray. I get a batch of these plastic growing trays every couple years and they work perfectly with both 2″ and 4″ square pots. The tray needs to have a solid bottom so the water sits in it! 

Some growers do this *before* they add the soil to the pots; I am a little lazier. I boil a large pot of water, get it to a rolling boil, then carefully pour it in each pot to saturate the soil. This immediately disrupts the thin layer of soil on top, so using my little Bonsai Rake, I just even out the surface again after I’ve poured the water. It’s okay if the surface isn’t completely, perfectly flat, as long as there’s some of the rich soil that the seeds can grab onto.

After this, leave it to sit and cool off for at least 5 to 10 minutes, preferably longer. The hot water sitting at the bottom will continue to heat up and steam the soil, and that should kill off any bugs or fungus. 

When you’re ready to start sowing, the pots should be comfortable to pick up and hold, and preferably be around 80 to 90F.  While the soil cools down from being sterilized, begin preparing your seed sowing station. 

Seed Sowing Station

Because this can make a mess and you’ll be dealing with very wet, recently saturated pots, it can help to put a towel down where you’ll be working. I use an old dog towel folded up so the water doesn’t pool on our counter.

I also  have a few items set next to me that are dedicated for just seed sowing. Anything that might also be a kitchen instrument I keep separately and labeled for the plants so I don’t have to worry about getting dirt and debris in the kitchen drawers.

I keep a box of Cling Wrap – basically, the non-sticky plastic wrap – next to me.

I also have tape handy; I cut up strips of packing tape because it’s what I have loads of, but scotch tape works well. If anything, scotch tape is better because it’s less sticky and won’t damage your pots when you take it off later.

PLANT LABELS are critically important. You will not remember what you planted or when. Write on the label using a pencil, not a pen or sharpie. Black markets and pens fade in sunlight, often faster than you expect, but pencil sticks around.

I like to have a set of tweezers handy, with this set being the exact set I’ve got for seeds and in the greenhouse for plant care. You can use them to place seeds precisely if you need to, rearrange things, etc.

A cup with play sand or just desert sand and something small to scoop it with is also needed.

Last but not least, a small squirt bottle with hydrogen peroxide. Any kind of bottle will do as long as it can make a fine mist; you’ll be using this as a final sterilization step.

It can seem like a lot, and it honestly sort of is, but for the number of seeds I sow this works very well. Some growers use plastic bags instead of my cling-film method, but I always have issues with mold, funk, or poor ventilation. 

freshly sown cactus seeds

To Sow The Seeds 

Finally, it’s time to sow them! 

You can use tweezers to carefully place them in neatly arranged rows, and include on your label how many you’ve sown so you can keep track of germination rates. I make sure my label has the full latin name, any seed lot numbers, and other details that came with the seeds. On the back of the label, I’ll put the date I’ve sown them to help me keep track of how old my seedlings are. 

Most often, I just tip the seed packet over and lightly sprinkle the seeds as evenly as I can over the top of the soil. I use the tweezers to even out any thick pockets of seeds, then cover the top with a very thin layer of play sand. 

Using my bonsai rake, I even out the sand and gently pat the sand and seeds into the soil, giving them a firm “set” in the dirt. 

After that, I mist the top with the peroxide, making sure the sand gets coated. This helps significantly in keeping algae from growing and leading to rot. 

Your final step is to tear off a bit of cling film, cut it to fit, and then use the tape to cover the top. 

Why the cling film? 

The reason you need to add the cling film on top is to keep humidity high for the seedlings. This is far from the only way to do so! There’s another grower in my neighborhood who sees a ton of success just using a sandwich bag to seal up his freshly sown seeds, opening it up from time to time to check on them or add water. 

I’ve heard of other growers just putting a pane of glass or plexiglass over a full tray of seeds, which would be ideal if I had to choose. It would just require some craftsmanship to build the case for it, and I am not quite that handy. 

I’ve tried using those little 6-cell garden seed starter kits, but found them to not keep humidity high enough and to be extremely finicky to work with and transplant seedlings. I’d notice seedling roots coming out of the bottom of the trays before the seedling bodies were big enough to support being transplanted, which is a frustration of such a short germination tray. 

The pots I use are 4″ square, but I’ve also had decent success with little 2″ square pots. 

How Long to Keep Seeds Covered? 

Once the seeds are sown, you should place them somewhere very bright but not in direct afternoon sun. I keep mine in a corner with east and north facing windows, so they get morning sun that fades to shade by noon. 

I also use a seedling heat mat to encourage germination, as the heat definitely seems to encourage them to pop up much faster than without. 

As for how long that should be…anywhere from a few days to a month! It depends entirely on the species you’re growing. This is one of the reasons I recommend Astrophytum capricorne or Astrophytum myriostigma as great candidates to learn with: they should germinate within a week at most. Their seeds are nice and big, easy to see, and it’s really easy to see when the tiny first plant bodies appear as little green nubs. 

You’ll want to keep the seeds covered for at least a few more days. Check your tray and keep the water topped up so the soil doesn’t dry out. With the seedling mat, they should be warm enough that you consistently see condensation on the cling film, which you can gently tap to see inside if anything has germinated. 

I eyeball my cacti to determine when they should be aired out. Once the plant bodies plump up a bit, and they at least double (preferably triple) in size compared to when they first germinated, that’s usually when I remove the cling film. For most of my cacti, that’s within the first week, sometimes two. I take the cling film off quite early compared to other growers I know, but as I keep them in a tray with water, they tend to not dry out too bad. If you’re really worried, a quick mist with a squirt bottle keeps the top of the soil moist. 

Once the seedlings are a few weeks old, they need light!

This next phase is the hardest part. The seedlings need plenty of light or they’ll etiolate, and in seedlings that causes such weak growth they rarely make it past the first year.

Good grow lights help, but you need to be cautious, as the same intensity that your cacti and succulents need to grow when they’re larger plants will scorch the seedlings.

I sow and grow my cacti during mid to late spring and through early summer, when nights are mild and days are rarely over 80F. This means after two or so weeks indoors, I can move the germinated seedlings to a shaded spot outdoors, and slowly migrate them to at least a few hours of outdoor morning sun.

I generally move mine out to the greenhouse to under my benches within 2 to 3 weeks, and move them to the top of the benches 2 to 3 more weeks after that.

You’ll know the seedlings are ready for more sun/light when they begin to get spines (if it’s a spine-growing species), and resemble extremely tiny versions of their adult counterparts.

Below, with my finger pointing at them, are some 2 month old Coryphantha elephantides seedlings. You can see the initial growth of spines, indicating adequate light, but the bodies are still generally green and plump. They’re also still quite small! 

ferocactus seedlings

At left, you can see some Ferocactus peninsulae seedlings the same age as the Coryphantha seedlings below them (2 weeks younger than the picture above, actually). They’re larger, have more spines, and are pink. 

If you look closely, you can also see that some of the Coryphantha seedlings are a dark green, almost brown color. 

This photo was taken when we’d had a few days of higher temperatures, and the tray had dried out before I could add more water. As a result, the seedlings showed signs of both water stress (too dry) and heat stress (too hot). If offered adequate water, the seedlings often tolerate high temperatures just fine. The photo above of the greener hued Coryphantha was after multiple days of highs in the greenhouse at 90F+. 

The difference?  I kept their water tray full, so they had plenty of available moisture to keep growing. 

At right are some Ariocarpus retusus and a few other friends showing what happens when you don’t sterilize your sand on top with the hydrogen peroxide. The algae isn’t a death sentence, but it does make it challenging for the seedlings to thrive. 

You can counter the algae by letting the soil dry out for a day before refilling your bottom-watering tray, or try misting with a 50/50 peroxide and water spray. 

As temperatures heat up and the soil dries out more, the algae will die off naturally, but it’s definitely frustrating to encounter on your seed trays. 

ariocarpus retusus seedlings

Growing cactus from seed is highly rewarding, and worth the effort!

Even if you’re not raising them to resell them as I do, learning to grow cacti from seed allows you to enormously expand the range of species you have access to. It also allows you to cultivate your own plants that are highly adapted to your growing conditions, which can be a major asset with some of the more finicky species.

If you’d like, try visiting my shop and ordering some of the same seeds I grow!