Designing Landcapes: How to build a stucco raised planter, in pictures, part I
Feb 05, 2024
By James Young
The following is a photo guide showing a method for building a raised planter out of masonry. But first some words:
Raised planters have many advantages over growing plants at ground level. They warm up earlier in the spring, extending the growing season, and in our cooler climate, maintain greater heat throughout the season because of this. They drain better, which is better for most plants. If you have clay soils, they are the answer to your dying plants’ pleas for a more breathable soil.
Raised planters are easier to garden. We’ve made them counter-top height for a client with back problems, allowing her to have a vegetable garden when she thought she’d have to give it up, maybe for the rest of their life. It’s also much more enjoyable to get out in the garden to weed, plant, pick vegetables or just enjoy your garden when it’s at waist height, even if you don’t have back problems.
Raised planters bring plants up close, so you see problems better so you can nip them in the bud. Using a cement-based stucco, these planters prevent slugs from crawling up the walls into the planter because they effloresce, creating a little salt on their surface, and slugs cringe at the mere thought of salt. Tunneling rodents, like moles or voles, can’t get past the underground concrete footing of these planters, protecting your precious veggies and other tasty roots.
Being up close you see plants, especially the smaller perennials and annuals, with a whole new perspective. The fragrance is more apparent. The colors are more vibrant. The little details, like the parts of flowers and the hairs on the leaves, are revealed to adults as a child would see them, bigger than life and with a new wonder.
Raised planters can be a beautiful design element in your garden. It’s hard to open a garden design magazine without stumbling across some form of raised garden. They have an intrinsic, universal appeal. They add a vertical earth element within the garden and anchor the garden with substantial mass. They can form an essential year-round backbone, counterbalancing the ephemeral plantings that surround them. They can provide a backdrop of mood-shaping color and catch the shadowy profiles of plants backlit from the sun or by night lights.
Can’t try to help people without announcing disclaimers; as American as apple pie.
Follow these instructions at your own risk. No guarantees are offered. What works for me may not work for you. I don’t know everything but the things I do know I may have taken for granted and forgotten to include anyway. If you use these instructions, there is still the very distinct possibility of failure and the resultant loss of your time and money. You’ll just have to move on with your life and accept responsibility, otherwise don’t use these instructions.
Before starting this project, at least read the following caveats.
First Caveat: There are certainly many different methods to build a planter to fit your particular needs. In this example, I’m using a very thin foundation (about 4 inches thick) to save on labor and material cost. The concrete had to be hand mixed because it was difficult to get the concrete in to where the planters were located. The risk is the foundation won’t be strong enough and cracks may form if the ground settles or expands. By all means go with a thicker/stronger footing as the extra concrete doesn’t cost that much if you don’t have to hand carry and mix it. If you have clay soil that expands when wet, you will definitely need a stronger and/or deeper foundation than shown here.
Second Caveat: You might not see it but the bottom of the footing in this example, at the shallowest point, is only 7 inches below ground. The frost line in the Edmonds area is more traditionally set at 12 inches. So, there is a risk of frost heave if we ever get an extreme ground freezing event that goes below 7 inches (frost heave is when frozen ground expands — it’s strong enough to lift even houses and crack their foundations). I don’t believe we’ll have a freezing event of that magnitude any time soon. It could happen though. Decide for yourself.
Third Caveat: There is a slight risk of a catastrophic explosion and serious debilitating injury. Oh, wait. That’s a caveat from a recipe for Cinnamon Rum Fireball Bundt Cake. Never mind.
Third Caveat: You could reinforce the blocks more than we did to further resist the expanding forces of the soil in the planter itself. A bond beam for the top row of blocks and a stronger attachment from wall to footing would be ideal if cost wasn’t an issue. Or it might be overkill. Better to limit the amount of water entering the planter during winter, which can reduce the amount of freeze-expansion of the soil. The soil in this particular case also drains really well. Also, these planters will get a low hoop of plastic to grow winter crops, which will also keep soil temperatures higher inside the planter, reducing freeze-expansion.
Fourth Caveat: The fourth caveat is that there are probably more caveats. I can’t think of every possible calamity but I’m know there’s plenty out there.
I hope I’ve made myself clear by now that’s there’s risk of failure. If not, stop reading this right away, forget about this project and do something completely safe, like a Sudoku puzzle. Oh wait, you could poke yourself in the eye with a pencil while doing that. Just sit in a chair.
Most raised planters I see are wood. As wood has a relatively cheap up front cost and is easy to work with, that’s understandable. The initial cost of masonry can be many times greater than wood unless you’re using really fancy wood or complex joinery.
However, when you consider that a masonry planter can literally last a lifetime and more, the long-term costs are much better for masonry than wood. Much of the cost of masonry is in the labor. The material costs aren’t that much more vs. wood. So if you DIY and you don’t count your own labor as worth anything (Ha!), then you can say masonry is close in price to wood planters. But even if you do count your labor cost (as you always should), masonry has better long-term value.
Wood will last as little as five years depending on quality and exposure to soil and moisture. Near the end of wood’s life, you’ll have to deal with ugly rotting; crumbling/splitting wood, splinters, loose nails and screws, and generally the last months of a wood planter’s life are unpleasant. Also, you don’t want to think about rebuilding something you already built; that’s a major drag. You’ve got better things to spend your life on than redoing something. Go with masonry, which can easily last decades.
In a related example, I can’t tell you how many wood fences I’ve seen that are ugly and falling down. Sometimes these ugly things are in a state of decay for years and that brings down the whole neighborhood. Outdoor wood objects look good for a short time, then they rot, they start to look ugly, and then they start falling apart. Even if religiously maintained, wood exposed directly to weather is not a winning combination. Spend the extra money on masonry walls and you’ll save money and have greater enjoyment in the long run.
Masonry has the advantage of greater heat capacity. This means it absorbs heat during the day when plants don’t need it, and releases it in the evening, which can be beneficial to plants in our generally cool climate. Wood doesn’t do that.
Masonry doesn’t require refinishing, generally, unless you’re really a neat freak. A masonry finish is very resistant to weathering and gains character with age. Specifically, the stucco finish we’re talking about here gains a patina over time that lends individual character to each planter and changes over time. Color can be incorporated into the stucco integrally, giving great depth that can’t be done with paint. Wood, if not painted or stained, will rot sooner. If you do paint or stain wood, you’ll have to do it over and over again as it fades, bubbles and peels, and generally doesn’t age gracefully.
Edmonds is a good place to start of culture of masonry in place of outdoor woodwork. There are already some existing examples of stucco masonry in downtown Edmonds. This is a good subject to explore later, but something to think about now. How do we want our neighborhood/city to look? Long term and substantial or cheaply built and transient?
Enough talky. Let’s get on with it.
1. After picking the proper site, dig out the ground to the proper depth and remove organic matter and humus filled soil. Organic matter will rot away and disappear, leaving voids in the soil. Voids do not support footings, so that’s bad. It needs to be removed.
Dig the footprint wider than your intended planter dimensions to account for footing and form board width. Minimum 8 inches beyond the wall dimensions on all sides should do it. (This planter will be approx. 69” x 147” so I dug out an approx. 85” x 163” area.) I’m using 6 x 8 x 16-inch concrete blocks to build the planter, available at any big box or concrete supply for a little over a buck a piece.
2. Level and compact the ground with a machine compactor (available at any rental center). Compacting is very important. Soft ground can break your foundation through lack of support. Part of the justification for the thin footing here is that we’re taking care to make sure the ground is really compacted. Ideally, you should use a machine compactor but thorough use of a hand tamper can work if you’ve got the muscles and there’s no other choice; it’s risky though.
You can get pretty close to level by using a 4-inch bubble level placed on the ground at many locations, then adjusting ground level as necessary, in a trial and error process. If you find you need to fill a low spot, use crushed rock (like 5/8 minus) and never backfill with soil containing organic matter, which will rot away leaving a void or soft soil. There are more expensive tools you can use to determine what’s level, like a transit or a laser level. That’s overkill unless you already own one. Instead you can level the top of the forms as shown in Step 3 and have the ground level (bottom of the footing) vary somewhat. Just try to get somewhat close.
Compact in all directions and go over and over it until the compactor starts to “jump” a little, indicating the ground is really hard. (If you ran your compactor over hardened concrete. you will get an extreme example of what I mean by the jumping action.)
Note: A machine compactor is heavy enough to require two people to lift it where it needs to go (170-300 lbs. depending on model). Keep that in mind.
3. After the ground is level and compact, cut and lay out boards for your foundation. First, make the outside form boards into a box. The box needs to be larger than the intended size of your planter walls by a few inches. I used deck screws for all the attachments.
Find the highest corner of the ground (use a 4-inch level placed on the ground and work your way around to get an idea what’s high and low) and attach the box form to a stake hammered into the ground at that corner. Just attach at ground level or slightly above. Then, work your way around the perimeter of the box form, level each board and attach it to stakes as you go. The boards don’t have to touch the ground; they can be off the ground up to an inch or so, which makes leveling easier and the foundation locally thicker, which works just fine (but don’t forget more concrete will need to be added to your calculations). After the entire outer box form is staked, go back and double check that it is all level and square.
4. Once the outer box form is staked level and square, do the same for the inner form. Make a box and then attach it to stakes to make it level with the outer form. Dimension the inner box to make a footing at least a foot wide all around.
Add intermediate stakes (not shown here) between your original corner stakes to support the boards and to help prevent them from bowing out too much when you add concrete. Place one about every 3 feet.
Hammer the stakes below the tops of the forms or cut the excess tops off your stakes if they won’t go into the ground all the way (there is a tendency for stakes to seek out the biggest underground rocks). Having a smooth upper surface on your forms uninterrupted by stakes sticking up will make leveling the concrete a lot easier later on.
5. The foundation’s toughness really comes from rebar. In the past I’ve bent it by hand just using my boot against the ground. You could do the same but later I bought a rebar-bender, proving that getting smarter with age is indeed possible.
A rebar-bender bar costs about $30 at any big box. You still have to use your boot to secure the other end of the rebar against the ground (or buy another of bender bar to hole the opposite side) but the bender makes getting tight corners easier and with less effort. You will have to practice to get the bend where you want it and at the correct angle.
Use your boot against the ground to secure the other end of the rebar while bending, or buy two of these to bend against each other.
6. Here’s how to do a rebar corner; the inner rebar track connects to the outer rebar track as shown.
Lay two ‘tracks’ of rebar all the way around the forms. Overlap the ends of rebar pieces at least 18 inches at the splices. Keep the rebar close to the forms but no closer than 1 inch at any point.
After bending all your bars and laying them out on the ground inside the forms, tie them together using bailing wire. At least two ties at each splice.
After it’s all tied together, prop the whole rebar assembly up on masonry blocks or mortar (but not bricks). The rebar needs to be at least 1 inch away from any surface (top, bottom, or sides). Shoot for placing it in the middle height of the footing for best strength for all load cases and for resistance to corrosion. Place a support about every 3 feet or wherever there is sag. When you pour your concrete, you don’t want the rebar to sag under its weight and end up out of place.
Also note in the picture that an irrigation pipe has already been installed, running under the footing. Now is a good time to add irrigation or electrical provisions. It’s not impossible to do it later, just more work.
7. I didn’t have any pictures of the actual mixing and pouring of concrete for this planter project (it was too hectic and dirty a day for camera work). However, here’s an example of a similar project by Blue Wheelbarrow involving concrete steps. I hope the picture doesn’t confuse you; it’s the same concept though:
Pour your concrete via wheelbarrow (preferably blue), or bucket, or directly from the truck’s chute if possible, or pumped in by a concrete pumping company. Fill to the top of the forms. Tamp the concrete with the back of a shovel to get it to settle into all the nooks and crannies (there are also special tools for this but they aren’t necessary here). If your form boards are off the ground a bit, it’s okay for the concrete to ooze out the bottom a little. However, don’t overdue the tamping in this case or it will continue to ooze out; let it set a bit first.
Screed concrete level to the top of the forms. Screeding simply means taking a piece of wood (or a trowel in the case of the picture above) and using a sawing motion across the tops of the form boards to get the concrete to settle to level with the tops of the forms. At the same time, the screeding action (sawing motion) will scrape off any excess concrete over the sides of the forms. You can touch up your screeding with a trowel but don’t overdo it at this point as water will rise to the surface of the concrete after screeding. Don’t scrape the water off; as long as you’ve finished screeding level, just let it sit and dry (may take a while depending on weather).
After the surface water dries, you can touch up any bumps or low spots with your trowel while the concrete is in its gel state. The gel state is a limited time frame between when the surface water dries off and when the concrete gets too hard to work. This is when the concrete is moldable and when experienced concrete masons trowel to level, trowel to improve surface hardness, trowel to create ramped up portions or drainage cuts and slopes if necessary, round the edges, score anti-crack lines, apply the surface finish, etc. You, however, should just focus on getting a really level surface.
If a lot of water comes up while troweling, you should wait longer; it’s still too wet, runny, and soft. It’s not quite at the gel state and troweling with too much water might ruin the strength of the concrete surface. Wait longer but test again often (try every 10-15 minutes) as you’ve got to be careful not to wait too long or it will become too hard and you can’t work it any longer. Welcome to one of the many difficulties of concrete masonry.
Other than troweling to level and removing air bubbles that pop up, there’s no need to apply a smooth finish to the concrete, just leave it somewhat rough and that will help the blocks stick to the footing later. While still in the gel state, insert your rebar stakes as shown in step 8.
Note: If you’ve never done a simple concrete pour, it may be time to hire someone. However, this is a pretty good project to practice on if you’ve never done it because it’s OK if the work is a bit sloppy. It’s just a footing for a planter right? No one will see it underground and the strength required isn’t super high.
You can call a ‘Ready-Mix’ concrete delivery company if you don’t want to do the mixing yourself. Tell the company what you’re doing and they can design a mix for you. They will also figure out how much concrete you’ll need if you give them the dimensions of your footing. Before you order from a ready-mix plant, be sure you have a wheelbarrow path from where the concrete truck will park to where your planter footing is located. Consider your wheelbarrow will be full of a heavy “live” load of wet concrete that tends to shift and slosh around. So, if you have steps to go up, it’s probably not a good idea to use this method.
If you don’t have an easy wheelbarrow path, you will have to have the concrete pumped in by a concrete pumping company ($$$) or you can bucket it up in five-gallon buckets from the truck (backbreaking work!). You can also carry dry concrete mix in individual 60-pound sacks to your site (also heavy work but not time dependent) and mix it on site in a machine mixer or by hand (heavy work and time dependent). The last case was what happened in this project (and also why the decision to go with a 4-inch thick foundation).
Other than this quick summary, concrete is too big a scope of subject to cover here. Good books and links can easily be found online. An individual bag of concrete costs less than $4 so I’d recommend practicing with a bag or two and see if it’s something you’d like to do.
8. Place pins at the core of each corner block while the concrete is in its “gel” state. This picture actually shows a concrete bolt drilled in after the concrete cured, a more costly option requiring a hammer-drill and special bolts, but easier to locate with regard to the block cores because you can lay out your blocks first to find the right spots to drill (not possible during the gel state of concrete). Still, because it’s cheaper, stronger, and doesn’t require a hammer-drill, you might be better off using rebar pins set into gel-state concrete instead of these bolts.
Also, in addition to the corners, place a pin every 3-4 feet along the wall. You will have to lay it out carefully according to your block locations to make sure it ends up coming through the open cores of the blocks and not at block edges. The pins should go into the concrete to about 1 inch from the bottom of the footing. Make sure it doesn’t go all the way through the footing and into the ground on the bottom of the footing or ground contact will cause the pin to rust out over time.
9. After the concrete has cured at least two days, take off your form boards. The inner boards may be trapped by the hardened concrete and have to be sawed out. While pulling the form boards out, a little force may be necessary but be careful not to damage the soft concrete. You don’t want to crack your footing at this stage. That would be a bummer.
Concrete doesn’t gain full strength until about 28 days and needs some moisture to cure properly. Treat the concrete gingerly for at least a week.
Lay out the first row of blocks to your intended dimensions. If you did your layout and design properly, the concrete blocks will fit nicely on your foundation with plenty of footing extending beyond the block edges, inside and out.
Congratulations, you’ve finished Part 1! Or at least you finished reading Part 1. A big virtual high-five for virtually finishing your project thus far!
Part 2 will cover the creation of the wall using masonry blocks and application of the surface bonding cement. Any questions so far?
James Young is the owner of Blue Wheelbarrow Landscaping in Edmonds.By James YoungDisclaimers First Caveat:Second Caveat:Third Caveat:Third Caveat:Fourth Caveat: