On this page is a variety of information to help plant growers: instructions on how to grow cacti and other succulents, on sowing, diseases, pests and more.
Sowing cacti is an easy task, but it requires precision. Sowing failure is mainly due to bad seeds, watering mistakes and poor control. Healthy seedlings should look like on right picture.
Seeds lose germination over time, even if stored in the refrigerator. The seeds of most species of cacti are best sown soon after harvest. Seeds of Astrophytum, Frailea, Copiapoa, Strombocactus and many others no longer germinate after one year of storage, and in most other species the germination rate is zero after two to three years. If we sow old, non-fertile seeds, they will usually mold within a few weeks after sowing.
Sometimes the seed doesn’t mold, and not germinate either. In that case, we don’t know if the seed is bad or we did something wrong. We continue to take care of sowing, as germination can be affected by humidity, temperature or the seed is dormant. In the latter case, it will germinate only under special conditions, so sometimes it helps to change the circumstances.
Pictured left is a pot sown with aged Astrophytum seeds two months after sowing.
Bad germination rate
Old, uncleaned or poorly stored seeds may still partially germinate, but the germination rate is low. In most cases, seedlings from such sowing soon die due to infections or poor vitality.
The seed coat is attacked by storage molds, which are not dangerous for seedlings, but cause rot. That attracts fungus gnats (Sciara coprophila) and continues to development of pathogenic fungi.
Here is the case of Astrophytum seeds from last season, harvested after few months and stored uncleaned in a box on hot place. Although a few seedlings have sprouted, the seeds are covered with mold.
Disinfect or not?
If the seeds are well washed after harvest, disinfection is not necessary. It is best to extract the seeds from fresh fruits and wash it under running water in a cotton cloth.
It is also not necessary to disinfect the substrate if it is good. For sowing I use a mixture of 70% volcanic sand, 20% clay and 10% Hygromull. Under such conditions, mold cannot appear or spread.
If the seed is already moldy in the fruit or if it is poorly washed, mold will appear soon after sowing.
On left picture is the Gymnocalycium seed, which was already moldy in the fruit and began to rot despite cleaning. In such cases, the mold quickly spreads and destroys all the seedlings. The left pot has a few seedlings they have already become glassy and will rot in a few days
Among the pathogenic molds that destroy seedlings are mainly Phytophtora and Fusarium. They most often occur from infected seeds or grow on dead tissue of fallen plants. They can also be transmitted by insects. Under favorable conditions they grow quickly and can destroy healthy plants also. The growth of fungi is promoted by organic nutrients, high humidity and high temperature, but it is prevented only by ventilation. Prevention of fungal infections with fungicides or disinfection is not effective, it helps ventilation and removal of infected material.
If the infection is local, as in the Fusarium case in the picture, this can be removed with tweezers, hopefully the infection has not spread to the substrate.
The biggest mistake when sowing cacti is drying out at the time of germination. If the germ dries out too much, it dies and after re-watering becomes food for fungi. Such seedling must be removed immediately, otherwise the rot will spread to all plants.
On the picture on the left, in the left pot are dried seedlings, but they are still stable because the substrate is still dry. In the right pot, the seedlings have already started to rot due to watering.
Spread of infection
Infections spread quickly if we do not notice this in time, and do not take any action. This is why precision at sowing is so essential. Sowing should be inspected at least every other day and any problems should be rectified immediately. During the period of intensive fungal growth, fungicides treatment and disinfection do not help.
If the rot spreads as shown in the picture on the right, it can only be prevented by removing all the infected part and drying the substrate. Nevertheless, we must expect the spread of the fungus to continue after watering.
If the seedlings are large enough, they can also be transplanted.
Peat based substrate
If the seed is of good quality, sowing on an organic substrate is usually very successful. The substrate must also be of good quality, suitable for sowing, not for planting adult plants. Seedlings in such a substrate grow faster because they have more nutrients and the substrate retains water longer. The bad side of this variant is that the infections spread from the seed or seed coat and spread very quickly (in one day) in the peat substrate to other seedlings. In case of infection, it helps to remove empty seed pods and aerate the sowing.
At too low a temperature, the seedlings may stop growing. Often the mold appears from the seed coat and damages the apex tissue. This occurs mainly in Thelocactus, but may also occur in Astrophytum and other cactus seedlings. The apex of the plant turns brown and sometimes it looks like there is a little hole on top. The seedling no longer grows and dies after a longer time.
Frequent transplanting accelerates the growth of seedlings, but it is very time consuming. When the seedlings are tilted in a pot, the substrate retains water longer and the seedlings begin to rot. The seedlings can be transplanted directly into a larger pot, where they can grow to a size for transplanting into mini pots. In addition, an even more airy but richer substrate can be used for transplanting, which accelerates growth and prevents plant rot.