The three most important variables:
We’ll examine these three conditions in greater detail shortly, but first let’s note that there are at least two different groups of cacti. There are the desert cacti which is certainly the first type to come to mind whenever someone hears the word “cactus”. However, there are also jungle cacti which grow in rain forests and other environments that most would consider the least likely habitat for a cactus plant.
Jungle cacti include those species in genera such as Acanthocereus, Disocactus, Epiphyllum, Hatiora, Hylocereus, Lepismium, Rhipsalis, Schlumbergera, Selenicereus, and perhaps a few others. Almost everyone has seen at least one representative from this group even if they were unaware that the plant was actually a cactus. The most common of these are the holiday cacti, Easter Cactus- Hatiora gaertneri, Thanksgiving Cactus- Schlumbergera truncata and Christmas Cactus- Schlumbergera x buckleyi. These plants are all true cacti despite their lack of big spines and inability to withstand the harsh conditions of the desert.
Most Jungle cacti are either epiphytic or lithophytic meaning they grow in trees or grow on rocks respectively. This type of plant gets its nutrients from the air or from dead leaves and other debris that may have collected in crotches, cracks, or crevasses. Those that grow in trees do so for support, but do not sap nutrients from their host. For best results we’ll want our soil to mimic these natural conditions.
Coarse orchid bark (about 25%), mix in some potting soil (25%), peat (25%), and the rest mostly pearlite with maybe 5% coarse gravel. The most important aspect of the mixture is good drainage. The pearlite helps create this by keeping the soil loose and “airy” and so does the orchid bark. Additionally the orchid bark tends to hold more moisture than pearlite or gravel. Pumice can be substituted for the pearlite. Keep in mind that the orchid bark will eventually break down into soil. This will create a very rich soil that may not be as effective in keeping the roots healthy. It isn’t a bad idea to re-pot these plants every 2 or three years with a fresh mix. The best time to do this is shortly after your plant has finished blooming. This is when it will be ready to start growing again.Fertilizer can also be added.
This is because a well drained soil is critical for keeping the water from rotting the roots off the plant. With the proper soil, however, watering is really quite simple. I water my Jungle Cacti about once a week. This is a good rule of thumb, but there are exceptions. During extended hot, dry periods I may water twice in one week. Conversely, when it is cool and rainy I might switch to every other week.Indoor plants should have less variation in watering needs.
The easiest way to gauge whether or not it’s time to water is to stick your finger in the top 1/2 inch of soil. If the soil is dry, go ahead and water. If it’s not, wait! Don’t let your Jungle Cactus go too long without water. If the stem segments are shriveled and the soil is dry, it is probably in need of water. Be careful! If the plant is over watered, the stems will also look shriveled, but the soil will be damp. If this is the case, do not give it more water. An over-watered plant will start to turn yellowish, then get more and more mushy and dark reddish-brown like a rotten apple. This usually happens from the ends first. This will continue even after you stop watering too much, but often you will have enough plant left to start over.
The ideal condition for Jungle Cacti is full morning sun and then shade for the afternoon. All the plants I have in this ideal condition exhibit robust and healthy growth.
There are three other lighting situations that are not as ideal, but often times necessary due to space constraints. These are morning shade/full afternoon sun, full shade, and full sun. It may seem that shade in the morning and full-sun in the afternoon should produce the same results as full morning sun/afternoon shade, but it doesn’t. This is because the temperature is cooler in the morning than the afternoon and for many plants the afternoon sun is a little too intense and plants will often take on a sickly-yellow appearance and may develop spots. In full-sun these symptoms will be even more apparent. As with most things in nature there are exceptions and some plants actually prefer full-sun and thrive in it. In full shade the plants will don a dark-green healthy appearance, but the stems will be stretched out long and thin in an attempt to reach more light.
Not only is light essential for healthy stems, it also triggers blooming in many species. In ideal conditions a particular plant may exhibit fantastic growth with many show-quality stems, but they won’t bloom. In this situation exposing the plant to longer and more intense sunlight will trigger it to bloom. Don’t forget that plants can get sunburn just like people do. If you have a plant that has been mostly shaded, don’t just stick it out in direct sunlight or you will certainly end up with a badly scarred cactus.
Desert cacti hail from throughout the arid regions of the America’s and surrounding islands. There are no desert cacti native to the old world and only one jungle species that occurs in Madagascar. Despite this, many people envision cacti growing in pure Sahara Desert sands with practically no water. This common mis-perception should not be in your mind when you are preparing an environment for your desert cacti.
Most cacti prefer a nutrient rich, rocky soil with good drainage. After trial and error and advice from other growers, this mix consists of 60% pumice, 20% coir, 20% Supersoil (topsoil). The pumice can be replaced with pearlite or vermiculite and the coir replaced with peat. I would recommend using only 10% peat, not 20% if you don’t use coir and make up the difference with more supersoil, pumice, or even sand. This is because peat tends to be rather hard to re-wet and can make your mix impenetrable to water. For larger pots or mixes directly in the ground I like to add 1 to 2 inch lava rocks from anywhere between 5 and 10 percent.It can make digging or transplanting more difficult because you’ll hit rocks with your trowel or shovel. Some people use earthworm castings for extra nutrients.
Remember, there is no one mix that is the perfect mix. Ultimately, you’ll want to experiment with different ingredients until you find one that works for you. Just remember that cacti roots need a well-draining, airy soil that will re-wets easily. Use whatever materials are most readily available to you locally. A simple observation to determine if your mix is cacti-suitable can be made each time you water by seeing how fast the water soaks through the soil. Always make sure that your pots have good drainage holes and that no water is able to sit in the bottom of the pot.
However the notion that cacti do not need water or that they actually must avoid water in order to survive is unquestionably false. The reality is water is essential for all cacti to live. Their reputation comes from their ability to survive in areas where water is available in small amounts or is delivered infrequently. Most desert cacti can sustain long periods of drought. This is because the last time water was available to them, they stored as much as possible in their tissues. Additionally cacti contain many features that enable them to keep that moisture and not dry up in the heat of their environment.
Whether potted or in the ground, a good time to water desert cacti is whenever the soil is dry. In hot, dry areas such as Souther California in summer, watering once a week is acceptable. In more humid or cooler areas, it may be three to four weeks before the soil dries enough to warrant more water. The key then isn’t to avoid watering, but rather just don’t over-water. With that said, it is still better to under-water than to over-water. Avoid watering if the soil is still moist. There are exceptions to every rule and just like choosing the right soil, you’ll need to experiment to find the best watering regime for your plants.
Unlike the jungle cacti, desert cacti typically prefer a lot more light. My desert cacti, which are planted right in the ground, get full sun all day long and love it. My potted plants, seedlings, and newly rooted cuttings only get sun for half a day. Full sun should be avoided as this is because the sun will heat the roots in pots to temperatures much higher than they can tolerate. One way to prevent this is by using white pots instead of black.
If you are growing your potted plants indoors, it will be highly unlikely that you’ll find a spot where your cactus gets too much light. In the case of limited natural light, full-spectrum fluorescent lights can be used to supplement or replace sunlight. You can get approximately 24 square feet of growing space under four 74-watt tubes for a cost that is under fifty dollars. It will be easy to tell if your cacti need more light. Cacti that are not getting enough light will exhibit thin, stretched-out growth. If you are unsure what normal growth is supposed to look like, look for pictures of your plant on google.