Building Raised Planters for Succulents, Cacti and Other Exotics
(Editor's Note: This article was originally published on September 26, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I have created numerous planter boxes. About 80% of all my plants are growing in them now, and I have discovered a few things that work well, along with many pitfalls. I hope to pass along some of these painful experiences to anyone planning on making some planter boxes of their own. Though I grow all sorts of things in planter boxes, most of my plants are succulents and they have some special considerations you may not need to be concerned about if growing other plants. Since my budget was fairly limited, I decided upon wood, for cost and ease of creation. This article is what I did, whether right or wrong.
When I first moved to this property, I was concerned about our pets (8 dogs, 2 cats and a bird) and how they would ‘get along' with our plants (and the thousands of plants yet to be added to the collection.) Most plants I grow are either toxic or quite hazardous for other reasons, such as spines. As a veterinarian, it just wouldn't look good to keep rushing my own animals to the clinic to treat them for environmental illnesses. One of the best ways to keep the plants and pets separate was to put most of the plants in raised beds.
(Left) A few of my plants awaiting reassignment . (Right) Dogs that need to be kept from the plants
Another reason for raised beds is my soil. It is nearly pure clay, which is not a friendly soil for most of the succulents and cacti (as well as the tropicals) I wanted to grow. Raised planters seemed the best option. This is where good planning comes into play. Too bad I am a terrible planner, but luckily, it worked out okay.
The NON-succulents also awaiting a home.
My yard was once a large lawn, a blank canvas upon which I could create my ‘art'. At times I reminisce about the lost open space, the lawn and the simplicity of it all, but it sure is a lot more interesting now. I first staked out the areas where I wanted planter boxes, and tried to plan the whole thing down to the inch. Eventually I just began to dig holes and put in posts, abandoning the rigid plans; things got a lot more interesting that way. I do NOT recommend doing things my way, though. It is best to stick to a plan. And before you fill up your entire yard with planter boxes, remember you might want a place for a barbeque, a shady place to sit or lie down, a place to play, a spot for a shed or greenhouse, etc. My yard was basically too tiny for most of those luxuries if the main goal was to have all the possible planting space possible. Work out priorities beforehand.
Blank slate (backyard)
By the way, if you are planning on sticking planter boxes on a lawn of Bermuda grass, it would be best to not skip the part about getting rid of the lawn first. I figured that two feet of soil on top of grass was enough to kill it off, and that would be the end of that. Bermuda grass laughs at two feet of soil, and for two or three years I battled the grass popping up all over the place. Ten bottles of Roundup concentrate later and the grass is no longer an issue. Still, ONE bottle of Roundup beforehand would have made things a lot easier. It is not easy spraying bits of Bermuda grass amongst delicate plants, trying not to kill them off at the same time. This is particularly true of plants growing in spiny, vicious plant collections far far away from reach. I may have lost several liters of blood in my Roundup efforts over the years.
For materials I used 2-by 6-inch treated pine. I have used redwood in the past and it looks great initially, it is lighter and easier to work with: fewer splinters and accepts screws with much less effort. But after a few months all the great color fades unless it's treated with a water sealer (though it still fades eventually.) Redwood costs significantly more and rots much faster if untreated. I suppose if you want to go through the effort of coating each board in a wood sealer, redwood would be a good option. THAT would have been far too much work for me, however.
(Left) A board and tools to measure and cut. (Middle) Early on I staked out planters with posts (soon gave that up.) (Right) Measuring is NOT my strong suit so sometimes things just didn't line up and extra pieces of wood would have to be slipped in to make things square.
Plastic boards are also available, but require more support (they bend easily under a lot of weight) and cost even more; but they never rot. If you can support them and afford them, plastic is really the way to go. I have also used 4-by 6-inch pine but it is nearly impossible to find screws long enough to go through the boards; hooking them together requires far more work and hardware than I am willing to put forth.
Railroad ties are excellent for planter boxes, but the creosote is very toxic, hard to saw through (wears down electric saw blades in a hurry, and WAY too much work to saw through by hand, which is how I usually have done it) and they are REALLY heavy. And in my dinky yard, the thickness of these massive logs would have reduced my planting area significantly.
For support, I used 4-by 4-inch corner posts, sinking them into the ground about 2 to 3 feet, and securing them with posthole concrete. I do NOT recommend doing this if you are renting the property, as digging out concrete posts is a LOT of work. Also be sure you don't have any utility lines in the way (the utility companies will usually come out to your property and locate the lines for free) I have had my share of experiences digging into pipes but thankfully nothing ever came of it (whew!). Be sure to put these posts in exactly where they are wanted as they are impossible to move once the concrete sets up. I also make sure I plant them straight up and down (nothing ruins a planter more than sloppy angles, and nothing makes a planter harder to put together than un-square corners and improperly measured dimensions.
Corner posts and boards.
Posthole concrete is cheap and can be acquired in bags small enough to carry. Best to dig deeper than necessary and then fill the hole with a bit of gravel or rocks (wood posts rot more slowly if not setting in mud.) Set the post then fill the hole approximately one-third with water, dump in half the concrete, tamp down and repeat until concrete is just below soil level. Most directions on concreting posts say to fill the concrete just ABOVE soil level, but then you have to deal with a concrete mound while putting in the support boards, so ignore that suggestion.
Posts being put in (and one waiting); taller posts used for an overhead shade structure AND corner posts for planter boxes.
I planned ahead and left the posts taller than necessary, figuring I could cut them down to size later. This extra height allowed me to place poles across (railings) the sides of the planter box (for looks or to keep dogs out), and gave me ready-made posts should I want to make a plant stand at the corners of the planters (turns out I pretty much made every corner post in the yard into a plant stand since I have so little room in the yard for free-standing plant stands). This was one of the few things I did right and planned in advance.
Virtually every corner post in the yard has been used as a plant stand. I was glad I made these posts tall!
Brick or stackable concrete blocks are also great to use, but brick needs reinforcement and footings that are way too much work (and/or money) for me. I have brick planters out front that came with the house and the brick is easily knocked down by aggressive root systems; aging concrete can give way on its own. The stackable concrete pieces are too easy to climb for the dogs, too thick (take up too much space and decrease my precious planting area) and a bit too heavy for my back. Stackable large bricks are great, look good, but cost too much money. But had I to do it all over again, I probably would do it that way (more permanent, looks good longer, and can support a lot of dirt without reinforcement.) NEXT time...
A mini planter of stackable bricks used as an accent for a prized plant.
Since I used 2-inch thick wood (really 1.5-inches thick--I'm not sure why that is; it's a construction thing, but seems a bit of a lie to me), 2.5-inch or 3-inch screws work well. I used deck screws, though drywall screws seem to work well, too. Drywall screws rust, but they don't seem to deteriorate any faster than the wood does; they are sharp and easy to screw. Also drywall screws don't tend to strip out. I do not use nails: too much physical exertion and I can't hit a nail straight anyway. Screws are easier to remove if it becomes necessary to disassemble the planter. Also I find hammering nails more likely to shift things about and not have them line up as well, and the wood is more likely to split apart. But those are really just excuses. I am a bad nailer.
Wood protectants increase the life of the planter wall. It is recommended to add more wood treatment/preservative (especially since there are cut ends on nearly every piece that expose the untreated wood inside.) Note: wood protectants are pretty toxic, so be careful if you have pets about. And some wood preservatives have toxic substances that can be absorbed through the skin (namely copper) so use gloves! Additionally, if you are trying to protect the wood, tarpaper works well as an inside liner for the planter boxes. I did not use this on most boxes (tarpaper is covered with tar and is messy to work with, not to mention frustrating and a lot of additional work.) But a single layer of tarpaper between wood and soil can significantly increase the life of a planter box.
Since I used the house as a back wall for this planter, I placed tarpaper against the house for added protection against rot and wear
If you have pets, and the budget, it would be best to make the planter boxes four boards high. I wish often I had done this myself. Two boards are useless for keeping pets out, though a significant savings. Four boards are tall enough to keep most dogs out, but costly and the higher the box, the weaker the top boards become. I compromised at three boards and watched with frustration as some of the dogs hopped right into the new boxes. So I ended up making rebar barriers above the planter boxes that made hopping in a bit more challenging... and actually looked somewhat ornamental.
Two different planters showing the railing added to keep dogs out.
For most succulents, potting soil works great for planter boxes, though I recommend amending it with a lot of pumice (or perlite) if that is available. Large silica sand (size 12 is a good one) is also great, but doesn't go far (MANY bags will be needed to fill any amount of space). Fine sand can actually make drainage worse so be careful to avoid the super fine sands sold at most garden outlet centers. For many of my planter boxes I just bought lots of bags of cactus soil and amended it with wood chips and pumice. But had I to do it all over again, I might have filled ALL of them with soil bought in bulk. And I would strongly recommend for succulent gardening a bottom layer of cheap but non-compressible material (rock, gravel, etc.) It helps promote drainage and fills the bottom half of the planters with cheaper material that does not break down significantly over time. Potting soils become packed in just one year of watering and soil levels can drop up to 8" (making the planter boxes look like pits rather than planting surfaces). For a lot of the boxes I ‘redid', I put in a lot of large, light, relatively cheap feather (a.k.a. ‘razor') rocks. These allowed me to save on soil, put in something that did not pack over time, and also made for a much more interesting planting surface. However, too much rock stacked up high also decreases planting area. And razor rock is SHARP (basically rough volcanic glass) so CAREFUL! But it is easy to chop holes in and use as built in pots as well. Because of the packing phenomenon, plan ahead and really mound the dirt up high, or you will end up--just as I have--taking many of the plants out later and replanting them after adding in a lot more dirt. This is OK when you are dealing with succulents as most move easily and tolerate this sort of abuse. But I also planted palms and large cacti in a lot of the planter boxes and these make such replanting operations complicated (many palms just don't move well, and huge cacti are literally a pain to move.)
(Left) Trucked in soil was used in the larger planter boxes. (Right) Bagged soil used in this later planter box.
Had I to do it again, I probably would truck in decomposed granite. It doesn't compact nearly as much and drains great and it's cheaper. Then I could have added amendments as needed. I would still use rocks for dimension and landscape variation. But I have to say, my plants have been incredibly happy with the potting soil and I am getting some healthier looking plants than I have seen anywhere else in my climate so perhaps the richer soils have not been such a bad idea, despite their tendency to ‘disappear' (see article on the metaphysics of dirt.)
One thing you should NOT do is add leaf litter or mulch to potting soil. This may improve drainage and perhaps make the soil richer and more nutritious (neither drainage or nutritive value are common problems with most potting soils though)... but it REALLY compacts down over time. I have this really annoying magnolia tree that dumps tons of leaves every spring... what a great idea to fill the bottoms of the planter boxes with this ready-made mulch AND a great way to dispose of all these leaves! The planters I have filled with magnolia leaves have had to have dirt added at least two times, and probably should be replanted a third. At this point, replanting is not really practical. In another planter I added several bags of cheap mulch which also compressed dramatically over time. In less than two years the soil level in that planter box has dropped by one 6-inch board.
The front is constantly bombarded with Magnolia leaves, so I decided to use them in one planter box; this shot of my first planter box on the right shows how much the soil has sunk. This is after removing plants and adding soil 2x already to above the level of the top board.
I have decided to remove a board in some planters, making them only two boards tall (they are so full of sharp plants now that the dogs have lost all interest in invading them and height is no longer necessary.) However, this makes the planters look less ornamental. I will probably have to tear these completely down and start over eventually.
(Left) Planter box with board cut off. (Right) The top board was removed completely to avoid digging out all the plants and replanting them (a few are pretty delicate and don't like being dug up.)
Let me say it again: potting or prepared soils settle! Always add more soil than seems necessary. Or plant knowing the plants will need to be removed in a year or two and more soil added. Or, perhaps water the soil very well to compact it and THEN add it to the planter boxes (still mounding it up as high as is practical.) If native soils or decomposed granite are used there will be less of a settling problem, but perhaps more of a weed problem. Now that I've done this enough I would choose native soil if I had any decent stuff to use. But I have clay and that is not a great soil for most cacti and succulents. And clay is infamously full of all sorts of hidden weed seeds as well of a multitude of organisms you might not want in your planter boxes.
A note about watering: it is of course best to plan ahead and put in a watering system NOW, not after the planter boxes are all done, filled with soil and plants. Ideally each planter box should have at least one sprinkler line to it for subsequent installation of drips or mini sprinklers for watering efficiency and effectiveness. However, this does take a lot of thinking ahead and is NOT my style, so I did not put in any sort of sprinkler system. I just have a lot of hose bibs around the yard so I don't have to drag a hose too far around too many corners. Since I did not put in a watering system, there is very little more I can say. But after redoing several planter boxes (removing plants and replacing them) I honestly am not sorry I don't have to deal with sprinkler lines, drips and other unnecessary hassles. I hope someone will follow this up someday with some suggestions on what works best for them.
(Left) One of seven hose bibs in the backyard. (Right) Plumbing all the planter boxes would have been a bit too much for me.
The basic planter shape is a box, or variations on the basic rectangle. My original plan was to make them all simple rectangles, but immediately I saw this was going to be fairly uninteresting. I find that corners, ‘Ls', and varying the sizes and shapes makes for a more pleasing appearance. However, specific designs are beyond the scope of this article and far too individual for me to make any serious recommendations. Just know, the more complicated the shape of the boxes, the more things that can go wrong and possibly the weaker the overall box becomes.
(Left) Two of the simpler rectangular boxes. (Right) The more interesting multi-cornered boxes.
I screwed the boards onto the outside of the posts for two reasons- it was a LOT easier to screw planter boxes from the outside than the inside, and MUCH easier to replace a board without digging out the soil. This creates a smooth planter box wall, not one with posts along the edges every four to six feet. However, screwing the boards onto the outside of the posts has the downside of all the soil (and plants) being supported solely by the screws and not the boards against the posts. If you do something as silly as planting large trees in your planter box, particularly near the edges, this will undoubtedly lead to the walls of the planter box falling off (yes, I have made that error, too, on several occasions). Still, I vote for boards on OUTSIDE of posts.
(Left) Downside to screwing boards to outside of posts: over time warping lifts boards away from posts. (Middle) If you plant a giant-trunked tree near a corner of a planter box, as I did with this Brachychiton rupestris, you can see how securely screws keep the boards in place... oh well. (Right) In some areas I have nailed copper flashing on to make the corners look better.
Once the boxes are built and filled it's time to plant. It may seem obvious to most, but it's probably best to plan ahead at this stage, too. For example, you might want to plant the largest/tallest plants near the back of the boxes (or the middle for boxes you can walk all the way around), and plant the smaller and more beautiful/delicate plants were they can be seen and appreciated more. Despite this obvious suggestion, I did not follow it closely, and of course with predictable results.
Here I planted a large cycad on left near front corner of planter, but the smaller, slow cactus near the back. Two years later you can begin to see the problem though it looked nice at first... and two more years, the bigger cycad covers up everything else.
Also it is best to know something about each plant in terms of how much sun or shade it needs. Light is extremely important for most succulents and many tropicals. Absence of light (i.e., shade) is the downfall to many a succulent. As the garden matures, the taller, more aggressive plants mature and hog more of the available light. Plants that need light but are getting too little are going to become weakened, more prone to pests and rot, and may thin themselves out of the collection; many of my plants have done this already. Put the sun-needy plants near the edges of the box or facing south, west or east.
Early on, sun exposure was not a problem. Everything got sufficient (if not too much) sun
But four years later, you can see many plants are obviously not getting the sun they need
It is also wise to plant those that need/want a lot of water nearer each other as well as put the drought tolerant plants together . Since I water with a hose, it sure is nice when I can direct the hose to an area rather to an individual plant while trying to avoid a rot-prone cactus right next to it.
Cacti planted near each other are easy to water. A few cycads and palms right in the middle of succulents are harder to water. Agave next to a water-needy palm was not really a wise planting move.
Also, from a safety standpoint, I recommend planting pointy, spiny plants away from the edges of the planter boxes (duh!... yet I still make the same mistakes over and over.)
Hard to see details in this photo, but tall, blue Cereus cactus is sticking into the aisle (very sharp!), and below it is a tangle of Boojum tree branches (nearly as sharp) that make walking past it a painful experience; second photo shows a large cycad seedling (Encephalartos whitelockii) sticking out into the walkway (very sharp spines!)... and this is just a seedling... what will it be like when it gets big?
Despite these somewhat self-evident planting recommendations, I placed the plants I liked best closest to the planter edges, and those I liked least at the back of the beds. As the planters filled up, I added plants where there was room. I planted small plants near each other, knowing they would eventually get huge (I tend to plant for the ‘now' and not for the ‘someday down the road'.) Of course now the planters seem randomly organized, and are becoming overcrowded. I knew this would happen and am slowly, sadly dealing with it. But I don't totally regret it, as the planters did look great for a while. And as I remove plants grudgingly bit by bit, they continue to look interesting and are always changing, keeping the entire effect from getting too static and boring. Still, best to do as I say, not as I do.
Fortunately succulents and cacti tolerate moving quite well (with a few exceptions.) And I have moved at least half the plants in my collection at one time or another (some of them three to five times now.) Moving also has the advantage of providing an opportunity to clean the plants of bugs and dead leaves, check the roots for rot, and keeps the garden in a constant state of change .
(Left) Planter being redone with all the movable plants taken out (you can see how much the original soil has sunk; it was originally level with the top board.) (Middle) Dug-up plants setting in wheelbarrow awaiting replanting. (Right) Rocks purchased to toss into planter under and above next layer of added soil.
Just remember these wooden raised beds are not permanent structures. Wood rots and there will be some attrition over the years (I figure I will be lucky if my planter boxes last ten years). Plan ahead about what you want to replace them with, or if you are just going to keep replacing boards as they fall off. At least with succulent planter boxes the soils aren't wet all the time and there will be less rot than if I had water-needy plants put in them. So maybe these will last a tad longer. Fingers crossed!
Before and after shot
Building a planter, early completed planter, and current shot of same planter from about the same angle
Before and after shot of another planter
another before and after shot
Some planters have so much stuff in front of them, progress is harder to appreciate
shot a few years ago and now
This planter has changed so much; it now has only two plants that were in it originally, and now so much stuff in front of it they can't be seen anyway
another before and after
then and now
early on, and currently
A few random shots of the planters now.
So if you want to erect fast, simple planter boxes for your succulent collection in a relatively small yard, you might want to follow some of my simple recommendations. And if something has worked far better for you, please write and tell us. It's not too late for me to change things again!