<b>Trees, Ornamental & Bedding Plant:</b> Succulent containers

Because of their small and spreading root system, many succulents grow well in pots that are wider than they are tall. Photos: Gary IrishSucculent lovers know no geographic bounds. There are fans of these enticing plants in the most unforgiving parts of the country, where cold dominates and rainfall is abundant. Yet it is this resilience coupled with a striking ease of culture, particularly in containers, that has endeared this varied group of plants to gardeners and landscapers since they first arrived in European and American gardens.

Plants like mother-in-law tongue (Sansevieria spp.) have been used in parlors and halls for decades filling out huge vases with their upright form and tall sturdy, deep green leaves that seem to grow in any situation and any light (including dim halls). But container grown succulents are also useful to gardens with their vast array of forms, color and styles allowing them to be used as a stunning accent, a colorful note in an odd corner of a patio or seating area, or massed together to create a potted garden of their own. They are useful to enhance the smallest of gardens – a patio, a tiny balcony, even a window ledge.

Plants, of course, have adapted to the conditions from which they arise and in the case of almost all succulents those conditions are long periods of little or erratic rainfall, high temperatures and often intense sunlight. But two adaptations in this enormous class of plants aid them in adjusting to the rigors of container culture: succulence itself, and their root systems.

Succulents Success
Succulents have specialized cells that hold water, releasing it for photosynthesis when soil moisture becomes too low for plants to draw water out of the ground. The most familiar succulents – aloes, haworthias, gasteria, ice plants, and sansevieria – have this tissue in their leaves. This  is why their leaves are fat, often fleshy and filled with a gel-like substance. In plants like succulent euphorbias and cactus, the stem is where these cells are housed and leaves are either absent altogether or show up only from time to time.

The root system of succulents is small in comparison to the plant and radiates out from the base as a fine meshed web. The roots are shallow as well, growing only inches below the surface and allow the plant to take up water in even the tiniest rain shower. As soils dry out, the feeder roots at the ends of the system begin to die off, signaling a shift to the use of the stored water. Once the soil is wetted the roots grow quickly, often within days, to take up water and dissolved nutrients once again.

Understanding these twin systems offers a road map to the culture of these long-lived plants and as with almost all container grown plants success begins with the soil.

Choose a soil mix that has as little peat as possible and drains very well. Use a blend of half this soil and half inorganic material like gravel, pumice or grit for cactus. Use a mix of 2/3 soil and 1/3 inorganic material for all other types. If your plants will be exposed to an abundance of rainfall, use the half/half blend for faster drainage.

Because the succulent root system is specifically designed to wick up water, it has virtually no capability to shut down as long as water is available. Ultimately, if water is constantly on hand, plants will burst or rot. To accommodate this type of root activity, maintenance involves watering thoroughly, but allowing the container to dry out between waterings. For cactus, it’s important that the entire column of soil is entirely dry and you can use a dowel, or pencil, or long screwdriver to find out. For most other succulents, a pot that is 2/3 dry is sufficient. Never use a saucer or other continuous watering system for succulents.

Culture Considerations
Many succulents have strong dormant periods. Adeniums, pachypodiums and rock figs lose most or all their leaves in the winter during their dormancy. Some haworthias, most ice plants and boojum are dormant in the summer. Watering such plants during their dormancy is tricky, a little may be fine, but in general they want to be dry during this period. This is especially true of those that are winter dormant.

In all succulents, the combination of cold, wet soils presents problems. Overwatering is easy because few are actively growing in the cold. The best strategy is prevention: Test the soil to be sure it is dry and don’t worry if it takes weeks between waterings.

Few succulents in the ground ever need to be fertilized, but it is helpful in containers. Use any all-purpose fertilizer with low nitrogen content (a number of 6 or less) and at half or less the recommended strength for container plants.
Water soluble fertilizer is ideal for most succulents. The most important thing is to use much less than recommended on the label, and never fertilize succulents when they are dormant. Cease applying any fertilizer at least a month before a plant goes into dormancy or the weather turns cold.

Container Options
The type of container is limited only by availability, garden style and the size of the plant. It is best to move plants up one pot size at a time rather than putting a small plant in a big pot. Too much soil means too much water most of the time, and rot is easily encouraged by too big a pot.

Because of their small and spreading root system, many succulents grow well in pots that are wider than they are tall. The container needs to have at least one hole in the bottom for drainage. In almost all cases, clay is preferred over plastic, chiefly because plastic can become brittle in high heat, holds too much moisture in some climates and is rarely good looking. Slipping a succulent that is in a plastic pot into a larger, more attractive clay or ceramic container is a great way to use decorative pots, vases or other items that do come with drain holes. However, when using such containers be sure to lift the plant out to water it; let it drain completely before putting it back.

Mulching succulents, especially in hot climates, is helpful for many reasons. Mulch cools the soil, slows down soil evaporation and reduces watering frequency. Mulch helps keep down splashing which is often how diseases spread among container grown plants. It is also attractive and gives a potted plant a finished look. Many growers of container succulents prefer inorganic mulch, like fine gravel or even chicken grit, but whatever you use, pick a product that enhances the beauty of the plant.

Mary Irish, former director of horticulture at the Desert Botanical Garden in Phoenix, is a freelance writer, book author and speaker. She lives in Scottsdale, Ariz.