Introduction: Hypertufa 'Seat Cushion' Planter

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I have to say that hypertufa ‘seat cushions’ are my all time favourite casting projects for the garden! The advantage of using hypertufa as a planter is that it's so much lighter than concrete.

We often find chairs that have been kicked to the curb but are still in perfect shape. For this project, whether they are metal, plastic or wood, you can work with any and all chair materials!

Making hypertufa is a fairly easy casting project, however it’s a long one because of wait-time. It can take anywhere from four to six weeks due to the curing time needed plus the time it takes to leech out the lime contained in the portland cement so it’s a safe container to house plants.

Given the long cure, timing is everything. If you start it in July for instance, it won’t be ready to plant until August – which is nearing the end of our growing season in Canada! The earlier you start, the more you can enjoy. However, if you wait too late in the season, you can always make your hypertufa in the fall instead. Then you can let the weather work its magic and naturally leech the planter over the winter. It will be ready for plants at the start of the next season and you won’t loose out on growing time.

Step 1: You Will Need

We're demonstrating this Instructable with a plastic chair, however we'll also show you how to work with a vintage metal chair near the end. To create a hypertufa chair planter, you will need:

    Step 2: Working With Plastic Chairs

    We came across this plastic chair at the side of the road. At first glance, my husband and I both thought the chair was cast iron, but on closer inspection it turned out to be a very convincing imitation. We loaded it into the car and brought it home before the garbage man nabbed it!

    Since the seat of the chair was already cracked, some of the work was already done for us! We punched out the centre section of the seat.

    We measured the circumference of the circle to determine the size of the bowls we would need to act as a mold for the hypertufa, then went out to our local thrift store to search for a suitable fit.

    Step 3: Determine the Size of the Planter

    At the thrift store we found a set of metal bowls for under $3! We tested the fit and the two larger ones were going to be just right for the mold.

    Step 4: Gather the Ingredients

    Hypertufa is made up of peat, cement and perlite. You’ll only need a bit of each so if this is your first project and you're not sure if you'll ever make another hypertufa, beg and borrow a few cups of each ingredient from family or friends who might have some extra to spare. We were able to get some peat moss from my mother-in-law so only had to buy the portland cement and perlite.

    Find a sheltered spot to work in – out of direct sunlight and wind – to keep your hypertufa from drying out too fast. We worked in our garage and laid down a sheet of plastic onto the floor in case we had any spills. Above you can see the bag of peat moss, which we sifted through to remove any large pieces of debris we didn’t want in our final mix.

    Step 5: Prep Work

    Don some gloves and spray the inside of the larger bowl and the outside of the smaller bowl with the cooking spray (make sure you get the rim too). Set the bowls aside while you mix the dry ingredients.

    Step 6: Mix

    The mix ratio is 1:1:1:1. We used a drinking cup as our measure and put one part water into a plastic pail.

    Next, we measured out equal parts of the peat, cement and perlite and placed it in a second pail so we could combine them together before adding the dry ingredients into the water. If you didn’t previously sift through your peat moss, you might want to remove some of the larger chunks of debris now to make a smoother mix.

    Once the dry ingredients were combined, we poured them into the bucket of water and mixed together thoroughly. Depending on moisture and humidity, you may have to add a little more water to get the right consistency.

    We forgot to add our liquid colourant to the water before adding the dry ingredients so ended up adding it in after. If your colourant is dry to begin with, however, add it into the dry ingredients instead. Read the directions of your particular product to determine how much to add.

    Our final mixture was the consistency of dry cottage cheese; just hydrated enough to pack.

    Step 7: Form in Bowl

    Pack the mixture into the bowl and distribute evenly. I tried to keep the thickness to an even inch all around. Insert the second smaller bowl on top and centre it. Continue to pack in the mixture around the edges of the two bowls until the mixture is level at the top. Tap the around the side of the metal bowl with a rubber mallet to release air bubbles.

    You’ll need to weight down the top bowl while it’s drying so it stays centred. We happened to have gravel, but you could add rocks, sand or anything heavy that will ensure it all stays put.

    Step 8: ​First Stage of Curing

    How long a hypertufa project takes to dry will depend on the size and thickness of your project, the humidity and the temperature. It will probably take anywhere from 2 – 4 days for the first cure. Just like every new project we try, it’s all about experimenting and learning from your mistakes to gain expertise.

    We placed the whole thing into a plastic shopping bag, sealed it tight and left it to cure for 24 hours on a level surface. You could use a black garbage bag, or plastic wrap, but make sure the plastic is tightly sealed to retain moisture and help it dry slowly.

    After 24 hours, remove the inner bowl, then wrapped it back up again in the plastic and set aside for another 24 hours.

    On the second day, we conducted a fingernail test to see if we could scratch off any of the surface. If it scratches easily, seal it up and wait another 12 – 36 hours. If you're impatient like us, release the outer mold carefully; it’s still really fragile! Since the project is still damp, you might want to wear gloves when you handle it.

    As you can see in the second picture above, we had to tap around the outside of the bowl to help it release. It was stubborn though, so my husband resorted to running a straight blade around the inside of the rim to loosen it. That did the trick, however we had it perched on top of an overturned bucket and it slipped and fell to the ground! In retrospect it would have been better to release it right on the ground so it didn’t have far to fall. Luckily it remained in one piece!

    The last picture shows how it looks once it is unmolded; we couldn’t wait to test the fit in the chair itself and we were happy with the results! That joy is short-lived though because you'll be wrapping the hypertufa back up in plastic again to cure some more!

    Step 9: Second Stage of Curing

    This time we wrapped the hypertufa in a black garbage bag. This stage lasts about three – four weeks; the longer and more slowly it can cure in a moist environment, the stronger it will be in the end.

    Now you have a decision to make on how you want to cure it. You can cure your project either in direct sunlight or in a shaded area; either one will work but a cooler environment will take longer to cure. If in a shaded area, open the bag every once in a while and mist the surface to keep it moist then reseal the bag.

    If you can place the hypertufa where it will receive direct sunlight you won’t have to mist it periodically. Our back patio faces south, so we left it there on top of a bench. Because the bag is sealed, it creates a humid environment. The heat will cause a lot of moisture to be released from the cement, which condenses on the inside of the sealed black plastic bag. This creates a water supply that will help keep your object properly hydrated while it’s curing.

    Step 10: Just When You Think You’re Done!

    After a month or so of curing, you’d think you’d be done, but you’re not! The portland cement contains lime that can be alkaline to plants so it must be leached out – either through a process of soaking it over the course of 3 days or by leaving it out in the elements to leach naturally before it’s planted (that’s where making your planter in the fall has its advantages).

    To leach the lime from the hypertufa, soak it in a container of water. Change the water each day for 3 days, then it will be safe for plants. If your project is too big, you can hose it down a few times a day for five days. If you prefer to let nature take its course, leave the planter outside for one or two months. Don’t forget to drill some drainage holes into the bottom of the hypertufa planter. We used a 3/8″ bit. You can further finesse it by sanding any rough edges smooth, but we left ours ‘rustic’ because the succulents will eventually hide the edges.

    Now you're finally ready to add plant material to your hypertufa planter. You can add flowers, succulents - or the best of both worlds: flowering succulents! Add a good base of soil into the bottom of the hypertufa planter before adding the succulents so the roots have something to grow into. I use a soil specifically made for succulents: it has a lot of sand so the soil drains well (succulents do not like to be waterlogged). The succulents should also sit above the rim of the pot so the leaves can’t rot in the soil.

    Depending on the size of your container, when you plant your succulents you can probably get away with five to eight as they will fill in with time. I leave a few inches of spacing between each one. If you’re the instant gratification type, you can pack them in, but I like to give the plants an opportunity to get bigger and spread on their own. The succulents you see in the plastic chair demonstrate the early stages of planting - between the first and second pictures, they are just a few weeks apart.

    As you can see by the pictures, we've created hypertufa planters in both plastic and metal chairs. See the next step to see how the succulents filled in over time in the plastic chair.

    Step 11: How It Fills in With Time

    You saw the chair planted in the last step. Now you can see how it looks when the succulents have had a few weeks to fill in. Pretty, right?

    Step 12: Working With Metal Chairs

    Retro metal vanity chairs like the one shown above are great for this project. I didn't have a before picture of my actual chair so I snapped this one at an antique market. It was identical except mine was bare metal so I spray painted it with white automotive paint. To get the effect of a seat cushion, the planter should nestle down into the seat so I removed the cushion and used a metal grinder to cut off the metal supports before I painted (2nd picture).

    We positioned this one by our rock garden over a fern. The fern starts small in the spring and then engulfs the chair by summer (as you can see in the previous step). It provides another layer of interest in our little backyard oasis :)

    For all the hypertufa planters where we've planted succulents, the majority of them are hardy so they will last over our Canadian winters. A properly cured and leeched hypertufa can withstand harsh winter temperatures without cracking. We’ve left hypertufa planters out during the winter for many years without fail, however we also sometimes store them in the garage until spring and bring them back out. Either way, the succulents seem to be happy.

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