Growing cacti successfully in our part of the world presents a nice challenge for the enthusiast. Most if not all of us who have taken a fancy to this highly interesting plant group, whether it’s purchasing one or two plants for the window sill, or building a large, diversified collection housed in a greenhouse, have probably killed a plant or two in the past. I’ve been growing these plants for over 20 years now, and I’ve killed my share of plants during that time span. There’s nothing wrong with that, as long as we learn from our mistakes and try to figure out how to do it better the next time. And don’t worry, even the best growers around the world, even in the cactus heartlands of the Americas, have killed their share of plant material. But growing the plants well vegetatively, and maybe even seeing them flower, these are sights that are truly rewarding and worth striving for.
Before getting into some general basics on how to successfully culture these plants over here, a few words on our environmental challenges are in order. Besides the increasing pollution and dirt in the atmosphere which tends to leave a dusty layer on the plants’ outer skin (and this has an adverse effect on the plants’ photosynthesis process), there’s always our tropical climate to contend with. The Philippines really has three distinct seasons — a very rainy season from June to September, a cooler (relatively speaking, of course) and less rainy season from October to February, and a hotter and mainly drier season from March to May. In Metro Manila, average temperatures are around 25-28 degrees centigrade, with a range of between 20 and 35 degrees centigrade. Average humidity is between 70 and 85%, but 100% humidity days are not uncommon.
Cacti come from North and South America and occur in a very wide range of climates. However, most cacti come from dry (vs. humid), temperate climates of the southern US and Mexico. These regions have average annual temperatures of about 18 degrees centigrade, although the range spans temperatures slightly below freezing to well over the 30s. While the days are hot, the nights are cool, and I mean cool. And remember that these areas also experience winter, without the snow but with prolonged cold temperatures. Cacti like ariocarpus, most mammillarias, turbinicarpus, gymnocactus, epithelanthas, lophophoras and astrophytum, prefer environments with fairly hot days but nice cool nights. These plants also go dormant (or stop growing) during the winter time. Quite a number of these North American cacti detest high levels of humidity and rainfall, something we have plenty of here in tropical Metro Manila. Baguio’s climate, with its average annual temperature of 20 degrees centigrade, warm to hot days and mostly cool nights, would approximate most closely what North American cacti have in their native habitats. Tagaytay would be next. Someday, I hope to have greenhouses in Baguio and Tagaytay. I’m sure my plants would grow even better in these areas.
Many South American cacti, on the other hand, come from areas that are a bit more tropical than their North American brethren. Here we are looking at annual average temperatures between 20 and 25 degrees centigrade with increased precipitation (i.e., rainfall). As such, many South American cacti like gymnocalyciums, discocactus, melocactus, uebelmannia and even some copiapoa seem to be easier to grow in our climatic conditions. Some South American cacti like rebutias, however, need to be treated more like their North American cousins, since these plants come from mountains and other highlands that also have quite cool nights.
But I have found that most of the genera of cacti mentioned above can still be grown quite well in Metro Manila. Flowering production generally suffers, though, because the plants really need the difference of hot days and cool nights to produce optimal flowers, particularly in the case of North American cacti. But in my case, I collect the plants essentially for the plants themselves, and it is just as rewarding for me if I can achieve the plants’ true vegetative form and growth patterns. Of course, the occasional flower is a nice bonus.
Different growers have different growing conditions and techniques which generally still produce good results. There are no one or two proven solutions. What works for one grower may prove absolutely disastrous for another. Here are a few basic tips to remember based on my experience and preferences:
Clay pots or plastic? Given that we are in the tropics with a high moisture content (humidity) in the air, one is safer with a clay pot. However, plastic also does quite well and is generally tidier and nicer to look at than clay (for me anyway). In my greenhouse in Makati, I grow my plants exclusively in plastic with generally decent results. The one thing to bear in mind when choosing a container for your plants is this: Plastic pots tend to dry out a lot slower than clay which is porous and absorbs moisture. You will need to water a lot less if you use plastic versus clay, something a very busy person might appreciate. For example, in the heat of summer, I water my plants no more than once per week, and when there is less direct sunlight toward the November to February time frame, I water once every two or even three weeks. On the other hand, I have friends who use clay pots, who may water even every other day during the summer!
There are two key elements to a good growing medium. The first element is the part which provides the nutrition to feed your plants. This first element is generally a good garden loam (soil), but organic material such as a well-rotted horse manure or leafmould (compost) can also be used or mixed into a soil base. There are other mediums which don’t have any soil but utilize peat and coconut coir. I personally would use these ingredients more for other succulents but not for my cacti. The second element is the part which improves the porosity of the growing medium, thereby allowing excess water to drain freely out of the pot, and also allowing the plant’s roots to "breathe". Sand has been the traditional component here, but the sand must be very coarse, or else it will tend to compact too much, retain water, and generally kill your plants in time. The fine dust-like particles from sand must be sieved and discarded. Beach sand is definitely a no-no. For me, I’ve stopped using sand and am using more perlite, broken brick and small gravel. These don’t cake, thus allowing excess water to flow away.
In terms of recipes, there are many possible combinations. If you are using a clay pot, a mix of 1 part garden soil, 1 part well-rotted leafmould or horse manure, and 1 part perlite with small gravel and broken bricks should do well for less water-sensitive cacti such as most mammillarias and gymnocalyciums. If you are using a plastic pot, I would cut the garden soil and leafmould to 50% and the perlite/gravel/broken bricks to 50%, thus improving the drainage capability of the medium. Finally for now, if you are growing some of the Mexican rarities like ariocarpus, strombocactus, epithelanthas and turbinicarpus which are quite water-sensitive, I would reduce even further the garden soil/compost part to no more than 30%, and increase the perlite/gravel part to 70%.
For cacti, I try to give as much direct sunlight and open air circulation as possible, given the constraints posed by my greenhouse location. While there are certain genera which prefer more shading, like most gymnocalyciums which grow amongst tall grasses in the wilds of Argentina, Bolivia, and other parts of South America, I find that these plants can also take a lot of direct sunlight, even noonday sun, if their roots are well-established and the plants are well-watered. But be careful with new plants which you are introducing into your general collection. If these had been housed in a sun-less environment for even a day (like the cacti you buy in
tiangges at the Ortigas Shopping Center, for example), don’t move these under direct sunlight right away, or their outer skins may burn and tarnish the overall appearance of your plants. What you should do is gradually acclimatize these plants to the sun by moving these from a bright shaded area gradually into the direct sunlight.
There’s a really simple rule of thumb for watering cacti. When in doubt, don’t. This is especially critical in our moist and very humid environment. If the roots of most any cacti are water-logged for a period of time, the plants will turn to mush and rot. Again, bearing in mind your container, your growing medium, the light conditions and the type of cactus plant, my philosophy is to water the plants only after the growing medium has completely dried for at least a day or two, maybe even longer in some cases. Most cacti are killed from over-watering than from any other cause. But these can survive even for a year without any watering (although the plant will not be in good shape, and we don’t want this either). In my case where I use plastic pots, I water once per week from around March to September, then only once every two or three weeks from October to February. If you are using clay pots, you may even have to water twice per week during the hot summer and succeeding months, then taper off to once every week or two during the rest of the year. Also, water more heavily during the summer months and give less water during the other months. One last thing here: I don’t like watering cacti when it’s raining or in generally gloomy, sun-less weather. These types of weather will cause the growing medium to dry out a lot more slowly, so I just don’t take any undue risks.
Cacti and other succulents do not require high doses of fertilizer. In fact, if you use general fertilizer and follow the instructions on the label, you will end up over-fertilizing your cactus and, ultimately, kill it. Cacti should only be fertilized during their growing season which, in the Northern Hemisphere (which is where the Philippines is located, but just barely!), is from around March to September. I refrain from giving fertilizer for the other months. I like balanced fertilizers like 20-20-20 (nitrogen-potassium-phosphorus). Look at the recommended dosage on the label, then dilute to only _ strength of this recommended dosage. You can fertilize every other watering. This also allows the plants to grow more evenly.
In the tropics, the two key pests I have encountered with my cacti are scales and root mealy bugs, with the occasional spider mite attack from freshly imported plants. I will write more about these pests in the future. I’m an advocate of using less rather than more insecticide, not just because I have small children around but because insecticide use is just plain bad for you. If I can avoid using these, I will. For scales, if the infestation isn’t significant, I remove the pest by scratching them off with a pointed instrument, usually the sharp tip of a plastic plant label. However, if the infestation is more severe, I use an insecticidal soap spray (which is generally much safer because of its more natural ingredients like pyrethrins) like the ones you can buy in supermarkets and garden stores in the US. Unfortunately, we don’t have insecticidal soap sprays available in Metro Manila (at least, none that I am aware of). This is quite amazing, and I hope the plant shops take note of this. In certain cases, I will use systemic insecticide granules mixed directly into the soil. The poison is then absorbed by the plant and any sucking insect is killed after it tries to suck the plant’s sap. Once or twice a year, I will get everyone in my house out for a day, I will don a face mask and rubber gloves, and spray the entire collection with a malathion mix. But do be careful when using this or any other insecticide. And read the instructions carefully before using these chemicals. Remember, your health is infinitely more important than your plants!
