Before we dive into watering needs, let’s start off on the right foot: Cacti are succulents, but not all succulents are cacti. Although they have similar watering needs and requirements, cacti are plants of a specific family while the term “succulents” refers to plants from many different botanical families. Cacti are distinguished by their rounder shapes and spikes of varying sizes. If what you were calling a succulent (which wouldn’t be wrong) has thorns all over it, chances are it’s a cactus.
Now that we’ve got that out of the way, let’s talk about our thorny little friends. They’re small, hardy, and often regarded as a great plant for beginners. Why? Because they can grow in a variety of spaces and don’t need the same amount of watering as a regular houseplant. Even with that in mind, though, getting the hang of watering them can be a bit touchy.
Even though cacti are pretty tough, their watering needs are different than that of other hardy houseplants like spider plants and pothos. Cacti don’t need to be watered as often, so if you aren’t used to caring for them, it can actually be pretty easy to over- or under-water them. It’s important to know their preferences; lack of familiarity is the most common cause of both drowning your plant and being overly-cautious of watering to the point that it shrivels up.
Improper watering is the most common cause of cacti downfalls, whether it’s too much or too little. Because cacti are native to desert areas and drier climates, they’ve adapted to store water over long periods of time and can retain moisture during periods of drought. They can only hold so much inside them, which is why over-watering can cause a lot of problems.
How often you water your cacti will depend a bit on the variety but mostly on the season, as far as frequency is concerned. The best way to know when your cactus needs water is to check the soil: If the top inch is dry, it’s time for a drink. For cacti, that means using the “soak and dry” method.
What is the soak and dry method?
The soak and dry method involves watering the soil thoroughly until some starts to drip out the drainage hole, then waiting until the mix dries almost completely before watering again. This method caters to their nature of storing water, and if done well will help them survive a period of under-watering should you need to travel or leave home (or if you just get busy and watering falls to the wayside, as happens to all of us now and again).
Watering during the growing season versus the inactive season
Like with many houseplants, the season plays a role in the frequency of watering. It becomes increasingly important that you get used to checking the soil to see if your cacti are thirsty. Generally, the rule of thumb is that during the growing season, a healthy cactus will need to be watered every one to two weeks. During the inactive season, the schedule shifts to once every three to four weeks.
Even then, checking the soil is important. Not all cacti are the same, and not all indoor environments are the same. Because there are a lot of variables, the only way to be sure your cacti need watering is by thoroughly inspecting the soil to see how dry it is.
One of the best indicators of an over- or under-watered cactus is its appearance, which is why you should take time to familiarize yourself with how it looks. When it’s healthy, what’s the color like? How are the spines? What’s its shape?
An over-watered cactus will start to look limp and as if it’s about to fall over, which is due to the moisture content preventing it from retaining its shape. An under-watered cactus, on the other hand, will start to shrivel and look as if it’s aged. Its color will start to change, and you may even notice that the spines are falling off because they’ve been weakened from lack of nutrients.
The other factor is the soil. If you’re not sure whether you’ve been watering too much or neglecting your plant, let the potting soil decide. Often with over-watered cacti, the potting mix is squishy, soggy, and may even have mold growing on top due to over-saturation. An under-watered cacti, on the other hand, will be sitting in bone-dry soil.
Could the container be the problem?
Ideally, you want to pot your cacti in a container with a drainage hole and well-draining potting soil. If your pot doesn’t have proper drainage, and you haven’t taken any steps to ensure that excess water has a place to go, then this may be the cause of your watering trouble.
If you find yourself consistently over-watering your cacti and they aren’t in containers with proper drainage, that doesn’t mean you have to get rid of the pot completely. Take the plant out, clean and dry the pot, dry off the roots, and before you repot with fresh soil, add in a small layer of pebbles or stones. These rocks at the bottom will allow excess water to drain out of the soil and keep the roots from drowning. Then, repot your cactus as you usually would.
An over-watered cactus can be difficult to save if you didn’t catch the problem early enough. As soon as you notice an issue, take the plant out of its pot and discard the soggy soil. Inspect the roots for rot — they should be white, but any black, brown, or mushy parts indicate root rot. If your cactus unfortunately doesn’t have any white roots left, that means it’s too far gone. When there are white parts left, though, you have a chance to save it.
Take a clean, sterilized pair of shears or scissors and cut away the rotting parts of the roots. Sterilize the shears again once you’ve removed all the contaminated parts so that you don’t risk spreading disease to your other houseplants. Repot your cactus in fresh, dry potting mix and allow it to settle for about a week before you water again.
How to help an under-watered cactus thrive again
When a cactus is under-watered, it can be tempting to give it a lot of water all at once to try and counter the problem; however, this can cause more harm than good. Watering too much, even when the plant is under-watered, has the potential to cause the same problems as over-watering (root rot and drowning).
The best thing you can do for an under-watered cactus is remain diligent. Follow all the above steps to pay close attention and determine when your cacti need soil and when they’re doing just fine. Watering regularly (according to their needs) will help the plants stay happy and healthy.
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