Free-Root-Run Raised Beds for Cacti and Succulents

Part 1: The Science Behind It

By J. Eric Driskill (March 2023)

Part 1 of a three-part series about using raised beds to grow cacti and succulents.

I built my first raised bed to grow cacti and succulents over 15 years ago. Since then, I have never missed an opportunity to transplant cacti and succulents into it in the spring and get them back in their pots in the fall, before temperatures dip too low. I have consistently used a raised bed every year since that first summer after I saw such amazing growth results for so many plants.

I realized you can buy smaller, cheaper plant materials and grow them into larger specimens quickly. You can achieve rapid growth in pots by overusing fertilizer, but that often results in a forced, leggy, unnatural growth form. I know a raised bed works; but when planning this article, I felt the need to back up my results with the science, listing and referencing the facts from valid research.

You can amass an extensive library of books specializing in cacti and succulents and many will have at least a little information about growing succulents. Many, in fact, mention suggested parameters for soil, water, light, fertilizer and types of pots (usually plastic or clay). Some books add information about water or soil pH, potting tools and staging. The vast majority of books in my collection, however, do not mention anything about growing these plants in a raised bed.

I can think of a few books that aren’t in my collection that I bet would at least cover preparing an area outside meant to grow winter-hardy plants year round. I have a few winter-hardy succulents in my yard planted in the ground, but I have always used my raised bed, specifically, to grow plants more rapidly.

You can certainly find biology, botany and horticulture articles that discuss how differences in pot or container size, including raised beds, affect plant growth. Most of these articles discuss food crops and yield variations related to container size. There are data in these articles that we can broadly apply to any plants, including succulents.

In “Pot Size Matters: A Meta-analysis of the Effects of Rooting Volume on Plant Growth,” an article published by Functional Plant Biology in 2012, Hendrik Poorter and co-authors reported that the doubling of container size increased biomass production by 43 percent, possibly due to an increase in net photosynthesis. This same article mentioned that a smaller container decreases the total nutrient content, which results in lower levels of nitrogen and phosphorus equating to a decrease in photosynthesis.

D. Scott NeSmith and John R. Duval considered the implications of container size influencing plant growth for other reasons in “The Effect of Container Size,” an article in the online publication HortTechnology. This article was specifically addressing the health and viability of vegetable and floral crops being transplanted from and to various size pots. Some of this information can be applied to succulents and the size of the pots we use, and how a raised bed, even temporarily, might diminish or eliminate the negative effects.

Aspects included in the HortTechnology article were reduced rooting volume, a decrease in shoot growth, reduced leaf growth and plant development. Also, small pots have more surface area relative to their volume, which increases soil and root temperatures. With the volume of even a small, raised bed, water, root temperature and nutrient availability are much more stable.

One book in my collection does address the benefits of a raised bed specific to succulents – Pachyforms: A Guide to Growing Pachycaul and Caudiciform Plants by Philippe de Vosjoli. He later published Pachyforms 2: Bonsai Succulents along with Rudy Lime. Vosjoli is probably better known as a bestselling author of over 20 titles on reptile care and vivarium designs. I would argue that the succulent hobby scored big when he delved into our hobby with two publications, and you should definitely add his books to your personal library wish list.

De Vosjoli discussed an important broad consideration: that the succulent hobbyist should distinguish between the two ways to grow our plants. “The pachyform hobby involves two distinct approaches to growing plants with the purpose of achieving different goals. One set of conditions aims to obtain rapid growth, the other in inhibiting the growth rate for the purpose of display.”

We see grand, old, mature specimen plants in person and in pictures of cacti and succulent shows, and we want “that” plant, or a plant that looks like that one. Although on the sales tables you often see a wide variety of specimen plants, the majority of plants there are seedlings or immature. These plants are certainly more affordable, but they aren’t the same as those huge specimens out on the show tables.

Quickly doing basic math shows that to start or quickly amass a collection entirely made up of large specimen plants will require you to either win the lottery or be independently wealthy. Most of us buy large plants when available and we have the funds, or we buy small, cross our fingers and begin the slow progression with hopes that those plants will one day turn into one of those wizened specimens.

De Vosjoli mentions that the fastest growth can be obtained using large planters or beds. He discusses several factors in his book to get our affordable small plants to the size we want as quickly as possible and then how, precisely, to shift gears and alter our growing techniques when our plants reach that size to maintain them at that size for display.

In hindsight, I am thankful that when I considered building my first raised bed, I didn’t start off with a literature search for research, because I fear I might not have built one. With little effort, you can likely find more articles about raised beds than I did for this article. You might even find research articles that specifically address succulents in raised beds. If you do, please consider writing an article for your local cacti and succulent society.

If you really want to benefit our hobby and these plants even more, you should consider applying for the research grant program available through the Cactus and Succulent Society of America. At the very least, I would encourage you to build a raised bed, experiment, take good notes and lots of photographs, and see the results you get. I bet you won’t be disappointed!

Part 2 of this series will describe in detail how to build a raised bed, including a materials list.

Sources

HortTechnology – The Effect of Container Size – NeSmith, D. Scott; and Duval, John – October/December 1998 –
https://swfrec.ifas.ufl.edu/docs/pdf/veg-hort/transplant/trans_cs1.pdf
Functional Plant Biology – Pot Size Matters: A Meta-analysis of the Effects of Rooting Volume on Plant Growth – Poorter, Hendrik; Bühler, Jonas; Dusschoten, Dagmar van; Climent, José; and Postma, Johannes A. – October/November 2012 –
https://www.researchgate.net/publication/236645802_Pot_size_matters_A_meta-analysis_of_the_effects_of_rooting_volume_on_plant_growth
Pachyforms: A Guide to Growing Pachycaul and Caudiciform Plants – Vosjoli, Philippe de – 2004