Cactuses not all the same, shouldn’t be treated same way

Cactuses are found in all parts of the world. They are even found in tropical rain forests. Different types of cactuses are found at high elevations in the mountains all the way down to below sea level in Death Valley. They can be found growing in Alaska as well as the tropics of Hawaii. Is that the same type of cactus? Hopefully, you said, “No.”

We select cactuses for the visual impact it makes in our landscape. Maybe because of its thorniness or lack of thorns, perhaps it’s the purple or red color or maybe because of its flower color or production of edible fruit and pads. Our reasons for selecting cactuses relate to our senses whether it’s visual, sense of smell or sense of taste. But it’s seldom because it belongs here in our Mojave Desert.

For these reasons it would be a mistake to treat all cactuses the same and expose them to the same intense sunlight that they might get on the west or south sides of a home or freezing temperatures during the late fall, winter and early spring of the Mojave Desert. One thing is for sure, all cactuses need good drainage.

Good drainage seldom happens in landscapes but it’s the most important requirement necessary for them to grow well. It’s best to know where cactus originated from which clues us in about where it might grow best in our home landscape.

Q: I have a variety of cactuses and several kinds of agave on drip emitters. Is it true that they should be turned off from November through February?

A: Most likely you will be watering at least once during the wintertime. Are we talking about cactuses growing in the soil or in containers? Plants in containers need water more often than plants growing in the ground. There are differences in cactuses coming from different parts of the world, their watering requirements and planting locations.

Cactuses from the dry deserts of the Southwest don’t require frequent irrigations like cactuses from wetter and cooler locations. Our cactuses coming from the desert Southwest would be fine without water the entire winter. Cactuses from other wetter parts of the world might be best watered twice during the winter.

Cactuses growing in containers might need water more often than cactuses growing in the ground. Cactuses growing in small containers should be watered more often than the same cacti in larger containers.

But, as a rule, water cactuses no more than about twice during the winter months. Other types of succulents, like gopher plant and aloe, require more frequent water applications than cactuses. For this reason, I would consider hand watering these plants and pay attention to when they need water.

Cactuses could be watered by an irrigation controller like other trees and shrubs in the landscape provided the soil surrounding their roots has good drainage. If they don’t, you will find out soon enough because they will die. How the soil is prepared at the time of planting has a big impact on how often they can be watered and their long-term survivability.

Q: I applied an insecticide to my agaves for borer prevention in March and April. Do they need to be treated like this again in the fall?

A: Insecticides applied once in March or early April is treatment enough for these types of borers for the entire year. Since it attacks only in the spring, treatment is done in the spring.

The type of borers found in cactuses are not the same borers found in trees and shrubs. They are a different insect entirely.

The cactuses most affected by these types of borers, a type of weevil, are agave types of cacti so the insect is called the agave weevil. More specifically agave weevils usually attack the American types of agave hardest.

The hardest-hit agaves are the large green American agave and the variegated types (yellow) of American agave. This weevil, or borer as you call it, flies looking for a mate in late February and March and lays its eggs then. It is thought they lay their eggs deep inside the crevices between the flesh and leaves of the agave.

The tiny grubs begin to feed at the central core of the agave. Feeding increases as temperatures warm and as these grubs get larger. Continuous feeding by these grubs causes the agave to collapse during the heat of the summer which is when we typically notice it.

Treatment at that time is too late. The new weevils have flown away.

The most common method of treatment is to protect susceptible agave from agave weevil before it collapses in the summer. Drench the soil around its roots a single time with an insecticide, either as granules or liquid, and lightly water it into the soil. The concept is to protect agaves by applying a poison close to where they feed, just after the eggs are laid by the adult agave weevil.

Q: I am considering moving my cactus. Is this a good time? Also, I’m thinking of taking some pups and just replant them. What specifics I would need to know?

A: Bottom line, the best time to move cactuses and replant their pups is in the spring and early summer. If I really want to split hairs, I will need to know the type of cactus.

But the ideal time would be as soon as temperatures begin to warm in February through about March. Before that time, the soil is still cold and so establishment and root growth are slower as temperatures get colder. During the heat of summer can be a little problematic as well because it’s not an ideal time for planting but it can be done.

I would leave them alone during the winter months when it’s cold and move them when temperatures start warming in the spring. Remember, all cactuses and other succulents don’t like their roots kept wet. So, water them into their new soil two or three times to settle it around the roots and then back off your watering frequency to normal irrigation cycles. Always improve the soil around cacti so there is good drainage or plants will have problems.

Pups are found on some cactuses as small plants growing close to the base of the mother plant. These pups are produced when the cacti are starting to reach physical maturity. In some cacti, this can be when it starts to flower.

If a cactus produces pups, it is always a good idea to take pups or start new plants when you move them. Unless you are a good gardener there is a strong possibility of losing plants during the move.

Pups are connected to the mother plant at its base usually on short rhizomes. Separating the pups from the mother plant always creates some damage to the rhizome on both pup and the mother.

A couple of days in the shade during warm temperatures will cause this damage to heal. After the pup and mother have healed, go ahead and plant in amended soil.

If you want to reduce possible losses to zero, use a fungicide like copper sulfate (Bordeaux) as a dust or dip on any plant damage. As soon as the fungicide has dried, plant them the same depth as they were growing in their previous location. Since the pups are babies, water them slightly more often than established plants.

In our climate, I water cactuses coming from our southwestern deserts about every three weeks when I am trying to push new growth. If you created good drainage, you could water more often than this. Watering every three weeks pushes new succulent growth and aids in their establishment.

Q: Is there a standard for watering cactus? I have many different varieties, from ocotillo, fence post, barrel and smaller cactus. I think I lost one to overwatering.

A: I wish there was. The watering requirements of cactuses depend on where their parents originally came from and whether they’re in the ground or growing in containers.

There are two types of overwatering: giving it too much water or watering too often (frequency of irrigation). Both types of overwatering are controlled by the irrigation controller with different settings.

Watering too often is controlled by which days of the week water is delivered by the irrigation controller. How much water plants are given is controlled by the minutes selected on the controller as well as the gallons per hour of the emitters.

Another problem I find in landscapes, usually by installation contractors, is how it is planted. Cactuses can be overwatered and continue growing without problems if they are planted correctly. All cactuses must have good drainage.

If the cactus is planted in the landscape with a hole large enough only for its container, it will die. How long it takes to die depends, but it could be one year to several years. These problems can be avoided by digging the hole wide and amending the soil to provide for good drainage.

An indicator when to water is cactus appearance. Because it uses internal water to supplement its needs, the plant shrinks in size or may appear wrinkled or dull as it’s using its internal water.

This indicator is not obvious to people who do not pay attention to the plants. These types of people observe the plant failing when it’s too late. By that time, the plant has shriveled, oftentimes yellowing and is close to death if not dead. If you are a careful observer and watch for shriveling or wrinkling or just that it doesn’t look right you will know when to water.

Like all good desert plants, cactuses grow when water is present and stop growing when water is not present. But many desert plants including cactuses indicate when it’s time to water through careful observation. If you are into that sort of thing, then it’s easy to water them by hand, infrequently, with a hose.

Most cactuses have shallow roots that can grow from the plant long distances. But if the water is applied automatically on a timer and with drip emitters then roots will grow where it’s easiest to get water. They never extend beyond this small area.

All that being said, I water cactuses originating from the desert Southwest about every three weeks manually during warm and hot months when I want to push new growth. I water less often when I am holding back their growth, but I observe them to know when to water. This might be once a month or two months when they have reached their size.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.