Wet climate cacti species.
We are located on the southern part of Taiwan, which is Sub-tropical in the north and tropical in the south (our location). This part of SE Asia receives very heavy rainfall in the spring, summer and fall and experiences typhoons (like a hurricane) in the summer. These types of storms bring in MASSIVE amounts of water, and kill many unprotected cacti species as its just too wet!
Here we will share what works good outside in these kinds of wet conditions. If it grows here in the rainy seasons, it can likely grow anywhere in the wet world. Please note that this page does not take into account *COLD* climates! All temps here are above 20C when it is this wet, that is very important to keep in mind!
Species that grow well outdoors year round here (Taiwan).
Notes on growing cacti in wet climates
There are some factors that play a large role in whether or not a cactus can survive in a given climate. Ground moisture, humidity, temperatures, sun strength, soil, pests etc. No one thing should be overlooked, as there is a balance that must be met. For example, Hylocereus undatus is well adapted to tropical areas and can be grown almost anywhere that is warm and a little wet. Gymnocalycium anisitsii, despite being on the same list above, must be treated far different from Hylocereus as it is not so well adapted to the wet. The soil must be different, it is best kept in pots so that it can dry out faster, for example. Below are some thoughts and experiences we have had growing cacti outside in this quite wet environment.
Soil: Perhaps the most important thing to consider is the soil type being used in the climate, that goes for all climates not just wet ones! In a wet climate we must look at a few things in a soil. Frist, how is the plants ability to deal with prolonged wet periods? 1 day, 1 week, 1 month, always? This will depend largely on the specie, but also the individual plant. Letís pretend we have a plant that cannot take prolonged periods of wet substrate and will show signs of rot after a week or 2, in our experience Gymnocalycium anisitsii is like this. With this in mind, we will probably want the soil more free draining, as to let water fall through better. Also using substrates that do not absorb water well are great ideas. Things like sand/grit/rocks, pumice, perlite are excellent options for this, and in fact make up the majority of our outdoor substrate mixes.
Perhaps we have a species that grow well in wet circumstances but do not grow well in hard substrates or clay heavy substrates, Pereskiopsis spathulata for example. When grown in hard soils, they tend to rot far easier than with slightly looser substrates. One must also think about the substrates invitation to fungus, bacteria and insects. Obviously half rotted compost is going to host things, both beneficial and not, which could possible lead to problems in your cacti....like rot.
In ground vs Potted: When planted in ground, your plants are really at the mercy of the weather. Some species such as Opuntia, Cereus, Hylocereus etc are well suited for just about any soil type in wet areas, but not all plants are. The ground tends to take longer to dry, in comparison to the same substrate in a pot. More surface area with a pot for the sun to hit and dry things out, so naturally we prefer pots for species that are not so tough with water. Also choosing a nicely drained, loose substrate will aid in faster drying times which may open the doors to more species outdoors in your area. In short, in ground is good for super tough, rot resistant species. Pots are ideal for slightly more sensitive plants.
Pests: Sometimes a cactus is perfectly fine sitting in a puddle of water for a week, certainly not the happiest times, but they push along regardless. Then along comes a snail and takes a chunk out of it. Much like breaking the front lines in your favourite war movie, this also breaks the front lines of the cacti defense (the skin) and this is often where rot sets in. Anything can cause this, but we find snails/slugs and caterpillars to be the biggest menaces to outdoor cacti! Many small pests like mites, mealy, scale etc are not present when its this wet (they get washed off by the rain more often than not). It's the bigger vegetarian critters that we need to watch out for. Other things like rodents, birds, ants, millipedes etc are all known to make some damage now and then. Your best bet is to bring the cactus under cover when this happens, if this is not possible, try to keep the area dry and treat it with sulphur.
Light: Drying times may be of concern with a certain plant, so placing plants in more sun is obviously going to dry things out faster. More sun=faster drying times, less sun=slower drying times. Pretty straight forward.
One more thing to consider, and this is especially true if the air is polluted where you live (acid rain) is the rain-sun-rain situation. With some species, when it rains then gets hot and sunny really fast, then rains and so on this can leave bad marks on the skin of the plants. it's the same reason you donít spray the leaves of your garden plants in the hottest time of the year. Here in Taiwan this causes some damage to some more sensitive species and leaves scars of brown when it is all finished.
Cold: A quick mention on cold, although this page is not talking about cold above. Many cacti species are able to handle quite cold temperatures, mainly the desert species as the desert usually reaches below freezing temps in the winter months. Tropical species are often far less tolerant of cold! One thing with cold is they should be kept ***DRY***. I grew a few cacti outside year round in southern British Columbia Canada with good success, but the trick is to keep them bone dry. Water and cold=ice=dead plants. Some can tolerate cold and wet, but it's a gamble often lost. Keeping them under cover is generally a good idea to protect from rain, snow and frost. And for Pete's sake, don't water them!