Cacti are amazing and unique plants, and they also need a specific watering regime. Cactuses are very specific about their watering needs and the way that they need to be watered. While all cacti need different watering frequencies, we will talk about general cacti watering needs. In this post, we will talk about how much water cacti need, how often to water cacti, which water to use and the correct watering technique.
How much water do cacti need?
First of all, let’s say that all cacti need different amounts of water and it will depend on many factors. Let’s review the main factors that affect how much water cacti need. A big misconception is that cacti don’t need any water, and this is not true. Cacti need water, especially during the growth period. Water is also important for photosynthesis and transpiration – water is lost during these processes.
- Does your cactus thrive in dry or more humid conditions? Cacti that are naturally thriving in hot and dry
conditions will need less water than those living in more humid conditions. - What soil are you using for your cacti? If the soil is sandy and light, the cactus will need more water. But if the soil is heavier, for example containing clay, cactus will need less water.
- Is your cactus growing at the moment? If your cactus is growing, it will need more water than when resting.
- Do the cacti containers have holes in them? If your cactus is in the container with drainage holes, you will need to water it more often.
- What is the temperature outside? In hot weather, you will need to water your cactus more often.
- Is the air dry? You will need to water your cactus more often if the air is dry.
- Does your cactus have small/short or long roots? Cacti with longer roots will generally need more water than those with shorter and smaller roots.
- What container is your cactus planted in? Cacti in plastic or glazed ceramic containers generally need less watering. This is because glazed ceramic, plastic and terracotta pots retain humidity for longer periods than other containers.
How often to water cacti?
You will mainly need to water your cacti during its growth period, which lasts from April to September. During this growth period, water your cacti once in around 7-10 days, but make sure the compost is mostly dry (not fully) before watering again.
If your cacti are outdoors, you might need to water them every 5-8 days. During the winter time (rest period), water your cactus only once a month or so. Some owners will advice to stop watering altogether, but your cactus will still need some water to survive. Water evaporation will happen even in winter, so make sure to lower the temperatures indoors.
Check the compost is dry before watering your cactus again. To do so, you can insert a wooden stick in the soil and see if it’s wet. You can also use a soil meter, which will give you light, moisture and pH readings from the soil.
Which water to use for watering cacti?
The best water to use for watering your cacti is rainwater, distilled water, or reverse-osmosis filtered water. Most reverse-osmosis filters go under the sink and filter the water as well as remove various impurities, making it safer for drinking and watering your cacti!
Try to avoid using tap water, as the minerals do really accumulate in the soil and your cactus might be very sensitive to them.
You can use a TDS meter like this to check how pure the water is. The measurement will be in ppm (part per million) and any number below 150 is acceptable.
If you use rainwater for watering your cacti, collect it and use as normal. If you don’t have any distilled, reverse-osmosis filtered water or any rainwater, you can use tap water.
But before watering your cacti with tap water, make sure to leave it in an open dish for a day. Also, boil it – this will make water softer. If you use hard water regularly to water your cacti, you will need to change the compost/medium more often to get rid of buildup minerals.
Please remember: Cacti only use a little portion of water in the compost for moisture/drinking. They mainly use water for transpiration and protection from overheating. So, underwatering can also become an issue in summer.
Should I use cold or warm water for watering cacti?
Cacti prefer warm water, and don’t absorb water that is too cold for them. So, the perfect water temperature for watering cacti is around 86-104 degrees Fahrenheit (30-40 degrees Celsius).
When you pour the 86-104 temperature water, it becomes cold after the contact with soil. Cold water is bad for cacti, as it won’t absorb it and it will cause rotting.
How to water cacti?
You need to be careful when watering cacti. First of all, make sure that the medium always dries between waterings. This is very important because cacti roots will start rotting if you overwater the plant.
There are two techniques for watering cacti: from above or below. Most cacti are fine with watering from above. But if a cactus has hairy leaves that are blocking the compost, you can water from the bottom.
Watering cacti from above or bottom
To water from above, slowly pour some water from a watering can with a thin spout. If the leaves are thick or hairy and you can’t water the cactus, use a saucer with water under the plant and keep it there for 25-30 minutes for the plant to absorb water. After that, throw away any remaining water.
Each cacti owner should decide the type of watering that he/she wants to use. To see which method is better for you, you can conduct an experiment. For this, take a two containers of the same size, with clear sides. Fill both containers with the same type of compost/soil and water one from above, and the other one – from below.
Then, after 1 or 2 hours, compare the soil in both containers. If the below method has worked and the medium is wet on the surface and bottom, you can start using this method for watering cacti. If the water stayed on the bottom, you better stick to watering cacti from above.
Whether you need to choose watering from above or bottom will depend of cacti’s shape and the soil, too. If a cactus is too thick and fills the container from both sides, bottom watering is more suitable. Same goes with the soil that is dry on the surface and doesn’t get wet to the bottom.
What time of the day is best for watering cacti?
The best time of the day to water cacti is around morning to mid-day. Never water cacti in evenings or at night. This is because in most Northern Hemisphere countries, including USA, temperatures can drop very low even after a hot day.
And even if you water your cacti in evening, low temperatures will make the water too cold which can cause root rotting. Water your cactus plant in the morning so that the water gets absorbed during the day and the medium gets dry before the next watering.
There is also a big chance of dew (if you live in the USA then it is very common) that will provide some moisture to your plant.
Mist your cacti straight after sunset – this way the stems will be still warm
Should I mist my cactus?
Apart from general watering, your cactus will also benefit from misting. Water your plant in the morning, and you can mist it in the evening. But only use a mister like this, that produces fine mist, and not droplets of water.
The best time for misting your cacti is after sunset, when stems are still warm from sun exposure. Use lukewarm water only. Don’t worry if your cactus is hairy – misting will only help to moisturize them and prevent breakage.
Don’t worry about misting a hairy cactus – it is very beneficial to prevent breakage!
Cacti roots are rotting, why is this happening?
If your cacti’s roots are rotting, this can mean that you have overwatered your plant once or multiple times. Waterlogging is the main reason for causing fungal diseases that leads to rotting roots in cacti. In this case, you will need to trim dead roots, treat your plant with fungicides and repot your cactus. Use fresh soil and wash the old container with soap.
One indoor cacti watering trick:
If your cactus is indoors, you can do this trick to help your cactus absorb more water in a way that mimics natural 
environment. To do this, water your cactus right before sunrise, and when sun is up, cover the cactus with some kind of a cloche or bell cover. When you cover the cactus, the sun hitting the cloche will increase the temperature and create humid conditions inside the cloche.
Leave this cover on for about an hour or so. After an hour, start taking the cloche out gradually (expose more parts of the cactus to the environment in 10 minute increments). This way you will avoid temperature drops. It is the best idea to perform this watering technique with indoor cacti.
These humid conditions (similar to a greenhouse) will help a cactus flower faster, grow roots and will improve its general health. You can perform this ‘hot bath’ technique once in a while, and even if you stop doing it, there will be no harm to your cacti. These hot and humid conditions mimic hot, rainy and humid summer weather in their natural habitat during growth period.
Thank you for reading this cacti watering guide! Make sure to check out the next article where you can learn about cacti light requirements!