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Growing Cacti From Seed

Cactus Propagation By Cuttings

There are advantages and disadvantages to growing cacti from seed. On the down side, it is slower than from cuttings, has a higher mortality rate, and the offspring is not always predictable in form and genetics. On the up side, this genetic variation may be exactly what you are looking for. Seed is also a lot easier to trade across state and national borders, and most seed is not affected by conservation regulation (CITES). Seed is also usually a lot more abundant than cutting material, especially when out of the native growing area.

Growing cacti from seed is easy, but a few rules need to be followed. These will be outlined in the following paragraphs along with some general recommendations and personal experiences.

In their natural habitat cacti usually germinate during the rainseason. The humidity is high and water abundant. This lasts for a few months and then dries up. Those seedlings best established will survive. In an artifical setting, this climate can be emulated, but we can extend the wet season somewhat to increase survival rates. The natural cycle however dictates that the arid zone cacti (eg Lophophora) need to be exposed to dry conditions within a certain time, or they are likely to die from fungal attack. Wet zone cacti (eg Trichocereus) will enjoy the extended wet period as long as it is warm enough to keep growing. When creating the environment for cactus germination you should always keep their natural requirements as outlined above in mind.

The medium should be mostly sand. Most growers use a mixture of 2/3 coarse sharp sand and 1/3 fine peat. This is also the usual cactus potting mix you can buy at garden centres. We have found the peat component to be a problem for some species as it locks in the grain and promotes fungal growth (especially under artificial lighting). We use well prepared coarse sharp sand only. You can either buy coarse sharp sand from your garden centre or cactus supply, or you can make it yourself.

To prepare the sand you can start with any grade, but the coarser it is, the less work you will have. Take a kitchen sieve and place a couple of cups of sand in it. Fill a large bucket with water. Now jiggle the sieve in the water so that small particles get washed out into the water (they settle at the bottom eventually). Keep doing this until no more particles wash through the holes. Keep the sand that is in the sieve - it is called 'coarse sharp sand'. This process is important, as it eliminates the small sand particles and silt that lock up the structure of the sand. Without removing this fine stuff most seed will rot rather than germinate.

To prepare the peat, use the same sieve and put in some fine peat. Agitate the peat and rub against the mesh. Collect the fine flakes that fall through as this is what you need to use for cactus mix.

Once you have your components for the mix (or just the sand), they need to be sterilised. This is important, as the young cacti are very prone to fungal attack and the more pathogens can be eliminated from the start the better. Place medium in oven at 200 deg C for 60 minutes. Once the medium is cool it should be stored dry and well sealed, or used straight away.

Most cactus growers will recommend to prepare your seed bed by watering with a systemic fungicide first. I have found this to be unnecessary in most cases, but it should be kept in mind if you have problems. Some systemic fungicides can inhibit seed germination and this is just one of many reasons why I prefer not to use them.

Sow you seed like you would any other, by placing at a depth of twice the size of the seed grain. Very tiny seed can raked into the surface or covered by sprinkling a small amount of sand onto them. Using a separate punnet for each species is recommended, as different cacti have different growth rates and growing parameters and may need to be moved at some time. Place all punnets (regradsless of species) into the same initial environment, which should be under a propagation dome (for high humidity), in 20% light (cool white fluoro preferably) at 25-28 deg C (soil temperature!!!). Cooler temperatures may slow or stop germination and increase the risk of fungal attack of the seed. If heating the propagation tray is a problem, temperatures of 20-25 deg C are sufficient, once seed has germinated.

Keep watering the seed and seedlings, ensuring that the surface never dries out. Initial growth of the seedling is fast for a few days, but slows as it uses up its reserves. After about 15-20 days the seedlings will require regular watering with a 1/8th strength fertiliser solution or hydroponic liquid. Wet zone cacti can stay in this environment for several months, but dry zone cacti will need to be weaned off the humidity over a period of several weeks by slowly increasing ventilation of the propagation dome. It is only the humidity which is a problem for them, but they will still like to be watered every few days. It is best to time the emergence of the plants into early spring, so that they can make use of a full growing season before going dormant in winter. When potting up, keep in mind that the bigger the cactus seedling, the better the chances of survival. I generally leave my seedlings in their punnets until they get too crowded.

Note: I have also germinated cactus seed in perlite, but the coarse structure did not allow proper penetration of the roots into the medium and all seedlings had to be moved soon after germination.