Watering Cacti and Succulents Outside in Pots

Q. I keep my landscape cacti and succulents on the dry side. But I am uncertain how much water these plants use when kept outside in small to medium sized pots. They don’t have a large volume of soil to contain their water supply.

Cacti are quite beautiful whether they are flowering or not. Thanks Agnes!

A. You are right. Cacti are watered less often when planted in the ground. They have a much larger root system compared to those growing in containers. Landscape cacti and succulents draw upon water their roots find in the surrounding soil. Potted plants are restricted to the water found only in their container.

Cacti growing in containers are managed and watered differently than cacti growing in the ground. Pay closer attention to water management and the soil needs to be changed every few years.

            Surprisingly, cacti and succulents of the same size kept outside in containers use about the same amount of water as those growing in the ground. But potted plants are watered more often but given less water during each irrigation.

Cactus should never be planted directly in most of our soils. Homeowners water them too often. For this reason the soil must drain easily. Soils that contain many small rocks, called course soils or coarse sand, can be used. When compost is used, make sure it does not more than 10% of the soil mix at planting.

            Water cacti and succulents more often in pots and containers. How often depends on the cactus and the soil.

            Cacti and succulents growing in the wild may have roots stretching distances 8 to 10 times their height. These large, extensive roots are important for their survival. When it rains, shallow roots “slurp” up the water quickly and put it into internal storage. After a rain, trunks, stems and fleshy leaves visibly swell with this stored water. They look “plump”. They react the same way after an irrigation.

Cacti and ornamental trees should not be mixed on the same irrigation valve. Either the cactus will get too much water or the ornamental tree will not get enough. There is no happy medium when mixing these plants together.

            Observe your plants to determine when to water next. To push growth, water more often. Water Opuntia or prickly pear cactus every three weeks during the summer to push new growth.             Watering frequently can cause excessive top growth with shallow roots. Eventually they fall over because they are top-heavy. Watering more often than this can kill it.

            ALWAYS allow the soil to dry between irrigations. Look at the cactus. If they are starting to shrivel, then it’s time to water. If the container is getting light in weight, it is time to water.

Most cacti roots are shallow and spread long distances. Watering cacti with drip emitters close to it is not a good idea or it can blow over in strong winds.

            Use a pencil. It is harder to push a pencil into dry soil than wet soil. Use a moisture meter. The meter should read “DRY” when it’s time to water again. Avoid glazed containers that are too small for a large cacti or succulents. Many cacti experts recommend porous, clay pots with drainage holes at the bottom. The width of the containers should be about half of the plants height.