DIY: How to Build a Raised Rendered Planter

If like me you have lusted over Pinterest images of rendered planters but ruled them out as too expensive, you may be suprised to know they are actually fairly easy to build yourself. My husband and I constructed one in our garden without any prior experience of building blockwork walls or rendering and we are delighted with the result. Ok… so it might not be as perfect as a professional job, but if you can live with a slightly rustic finish you can certainly save a few thousand pounds!

Before we started we watched a lot of tutorials, read many DIY advice forums and consulted the builder at work on the best way to go about it. To share the benefit of our research, I’ve put together the simple how-to guide below. I hope it inspires you to give it a go!

Firstly you will need:

A shovel, aerated concrete blocks, granular sub-base, multipurpose mortar/render mix, rendering trowels,  a sponge, a metal straight edge, rubble bags, garden staples, paint

1. Measure the space and make a plan!

This may sound obvious but measuring the space carefully and working out how to fit in as many whole blocks as possible will save you a lot of time in the long run. As well as having to cut less blocks, it can also means you are less likely to accidentally over-order.

2. Dig a hole!

Hole in ground

With a large shovel, dig down to find ground solid enough to support the planter. We ended up digging down around 300mm below the surface of the garden before the soil turned to a more solid clay substrate.

The digging produced a huge pile of soil/mud, but don’t worry as this can go back in the bottom of the planter once it’s complete. It’s a good idea to keep the pile near the planter so its easier to transfer back.

3. Create a solid foundation for the planter

To ensure the planter doesn’t move/collapse spread out a couple of bags of granular sub-base (aka MOT Type 1) underneath where you are going to lay your blocks. On top of the granular sub-base, we poured a thick layer of mortar, approx 60mm deep and slightly wider than the block itself. All good DIY homeware stores have bags of ready-mixed Mortar, we bought Tarmac ready to Use Multipurpose Mortar from B&Q. All you need to do is add water and mix really well (otherwise the blocks won’t adhere properly). The consistency in the mortar you are looking for, is that of toothpaste, your trowel should be able to stand up in it when dropped.

4. Lay the blocks

first course

For the building the walls, we used aerated blocks as they are much lighter and easier to handle and it is a good idea to get them delivered to avoid ruining the suspension of your car! Most homeware and merchant stores such as B&Q will offer a delivery service.

Starting at the corner of your planter, apply approximately 10mm thick mortar onto the side of the first block and lay it into the wet mortar. Use a spitit level to check that it is vertically and horizontally aligned and tap the top with a mallet if it needs adjusting. Repeat and add the next block. The downside of using aerated blocks is they have little weight to hold them in place, so you can’t fiddle with the block once bedded otherwise it will become loose.


Stagger the joints on each course so there are no weak points. If you need to cut the blocks you can use a chisel and hammer and it should break off in a straight line. Build up the courses of the blockwork until the planter is at the required height. We built ours up to 600mm above the ground level. We went a little higher than normal as we are going to put a bench in front of it.

Once complete, fill in all the gaps in the mortar and check the blocks are fully fixed in place. Leave it for at least 24 hours to dry and settle.

5. Applying the render

Spray the blocks with water (to make sure it sticks to the blocks better when dry) and apply a thin coat of the render mix with your largest trowel. As ours was multipurpose, we used the same mix as the mortar.  Apply the render  in upward motions. If you are having trouble getting it to stick, wiggle the trowel slightly as you apply it

Continue the render on the inside faces just underneath where the soil will sit. Lightly scratch lines in the render with your trowel to ensure the next layer sticks to it. This is the scratch coat.

scratch coat

Once dry apply another coat. If you are able to do it smoothly enough this can be your final coat (however we did three coats, so don’t worry if not!)  To create sharpe edges use your smallest trowel to mould the render.


Whilst your render is still wet, lightly run a straight edge over the surface to skim off any uneven bits. If you don’t have a straight edge you can use a long metal ruler or anything similar.

Gently rub a damp sponge over the render to create a smooth finish and repair any uneven areas if you have them.

6. Waterproof to stop cracking

waterproofingLeave the render for about a week to dry and then, paint with a good masonry paint. We went for white, but be warned it is not particularly forgiving with imperfections!

Use garden staples to fix rubble sacks around the inside of the planter . This will stop water sitting against the blocks which would eventually lead to the render cracking. Fill the planter with your chosen mix of compost/topsoil up to the level of the waterproofing.

7. Planting!

And lastly the most fun part… the planting! These kind of planters look great with dramatic vertical plants. We planted a cherry tree at one end and tall ornamental grasses at the other end for balance. For interest at ground level we planted beautiful pink Cordylines and more blue ornamental grasses which has added gorgeous texture.

planter ixed



I hope this inspires you to have a go yourself. I would love to hear about your DIY project 🙂

If you are still nervous, check out these other great resources for building planters:


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