Growing cacti from seed
The Takeaway Tek
This technique is a classic aussie way of growing cacti from seed. Everyone has their different adaptions and preferences but this is mine. I've been growing this way for many years with great success.
Take some seed raising mix, propagation sand and zeolite and mix in equal parts. This is all available from bunnings. The zeolite is sold in the pool section as zeo-clor but is quite expensive so can be omitted from this if needed. if you choose to omit it then just use 50/50 seed raising mix and propagation sand. An interesting addition can be a little bit of ground cinnamon for its anti-microbial properties.
Put a thin layer 3-4cm or so in a plastic takeaway container. Ideally this will be reused waste, saved from going to landfill! Tamp the mix down into a level layer using something flat.
Once cool take a permanent marker and write the date and species you are sowing. I also like to include a plant label inside the container because the permanent marker fades over time. Graphite pencil lasts for decades on plastic plant labels so I recommend using that.
Sprinkle the seeds evenly across surface. A max of around 50 – 100 seeds per tub. Then tamp down again lightly and spray evenly and lightly with seaweed solution. Add just enough water using the sprayer so its just damp, not sopping wet. You don't have to use seaweed solution like seasol but I highly recommend it.
Close the lid and place in a bright spot well away from direct sun, if there is any danger of direct sun at anytime cut a piece of 50-75% shade cloth and drape it over the tub. You may need to double it up initially, if the seedlings go red, you need more shade. I find that they really need minimal light when germinating and in the first few months. Down the side of my house is perfect or you can leave them on a windowsill.
Germination starts in 2-3 weeks, spring and autumn being good times for most cacti with moderate temperatures.
Leave the lids sealed for up to 6 months, it acts like a mini terrarium, recycling moisture. After 6 months it’ll need a drink, but then you can reseal up to the 12 month mark by which time they should be ready to separate out and pot on. Mine are ready for the big world after about 1 year.
Only open if you see fungus starting, in which case cracking the lid a while so excess moisture is decreased. I tend to spray with a 3% solution of hydrogen peroxide (available at the chemist) if I notice any mould growing. This will not harm the cacti but kill the mould instantly.
If its too dry, re-wet with a 1/8 strength solution of seasol or even powerfeed.
The cacti are ready to move on once they have a proper set of spines and a little girth. I find small cacti grow better communally, only being divided to their own pots once about 10 – 20mm tall.