We regularly get questions regarding cactus care and how often to water a cactus plant. This article will seek to help those caring for their cacti or succulents on how to best water them. Before we begin offering advice on how to best water, its critical to understand that there is no "one best method". The best method entirely depends on the circumstances a cactus is living in. The factors that determine what sort of watering schedule a cactus should have are listed herewith, each one will be explained further below.
What are the conditions like where the cactus lives? Is it on a very bright windowsill reaching lots of light the entire day, or is it in a darker portion of a home? Is it an outdoor cactus or indoor cactus ? A cactus or succulent that is exposed to high levels of light is also exposed to higher levels of heat as a by product. Higher light can mean quicker growth, while higher heat translates to into higher water loss from evaporation. A cactus that is located outside will encounter wind, wind has a drying factor on cactus soil. If your cactus is in a warm or hot sunny area of your home watering should be more regular. It the succulent cactus is outside, the past and future weather needs to be accounted for when caring for your cactus.
Cactus Soil Type
Different cactus soil types mean different water holding capacities. This couldn't be more important for any other genera. Cacti are very sensitive to overwatering. A damp soil that allows a house plant to thrive could be detrimental to a cactus. This is because cactus roots are prone to rot when they sit in a wet soil for too long. This rot spreads through the roots and into the body of the cactus damaging or killing it. This is why a good cactus soil is one of the most important elements of proper cactus care. A soil that tends to hold water better will require less water than a porous speciality cactus soil. Ideally, you want a quicker draining cactus soil. Aim for a 70/30 Grit/Compost mix.
Cactus Pot Type
Cactus pot type is important because the type of pot used effects how quickly the water in the soil evaporates. A plastic pot traps water better because it is not permeable, water cannot escape though the walls. A terracotta cactus pot or clay cactus pot is porous and water will evaporate through the sides of the pot the cactus is planted in. Water less if your cactus is potted in a plastic pot, and water more often if the cactus is planted in a terracotta pot.
Genus of Cactus
There are many types of cactus. The genera of cactus plays an important role because not all cacti have the same environmental conditions in the regions they are endemic to. Mountain cacti such as Trichocereus pachanoi, Trichocreus peruvianus and Trichocereus bridgesii live in much wetter conditions, growing in richer soils. They can handle higher amounts of water and be forgiving about it. Mexican dessert cacti such as Ariocarpus, Lophophora, or Geohintonia grow naturally in arid conditions for much of the year, when there is precipitation it freely drains through the mineral limestone soils they live in. Understand where your cactus grows naturally, its unique climate, and soils, to appreciate how much water it requires.
This can all get a little confusing when you have a combination of the various factors above. Fox example you may have a mini cactus or a succulent planted in a rich compost in a clay pot. In these sorts of situations it is best practise to analyze the soil moisture before watering if ever unsure. To measure the water levels of the soil accurately you must do so a few centimetres below the top of the soil, as the top layer of cactus soil will always dry out the quickest. You can use your finger to feel for dampness, use a tool that measures relative cactus soil water levels or make decisions to water or not based on the weight of the succulent cactus soil. The most important thing to remember is, if ever unsure, it is best to not water. No cacti in cultivation have ever died from drought, but many have perished from overwatering.
The best way to water a cactus depends on the four cactus succulent factors cited above. Cactus soil type, cactus pot type, genus of cactus and the cactus environment. A little can go a long way. Cacti have evolved to make the most of the limited resources they have access to. Cacti thrive on neglect.
If unsure its always safer not to water a cactus.