Modern Concrete Planters DIY Tutorial

Today I am excited to share a completed project I’ve had on my mind for quite some time! I made modern concrete planters using diaper boxes!

Step 1. The first step was to prepare my heavy duty boxes. I used diaper boxes because I had many left over and I used packaging tape to seal all the spots the concrete might seep through. You especially want to make sure you tape down the insides so that the surface where the concrete is poured will end up smooth!

Step 2. Next I chose a smaller box to make the cavity for the center. You have to ensure 2 inches of space around the whole perimeter so the concrete is thick enough to be strong. After taping up the sides of the smaller box for the inside, I had everything ready for my concrete mold.

Step 3. Now it’s time to mix up the concrete. Be sure to wear a ventilation mask, eye protection, and gloves when working with concrete. I used Quikrete’s ready set dry mix. I grabbed a bucket that could get dirty and added the dry concrete mix. Using a trowel, I broke up the clumps. Then I used a hose to add water into my bucket! This wasn’t an exact science for me, I just added water bit by bit until the concrete mix was the consistency of peanut butter. It was tiring on my wrist to mix with a hand trowel, so I would recommend using a garden shovel if you are mixing concrete at home.

Step 4. Then I started filling my diaper box with the trowel. I got about 2 inches deep on the bottom of the box before I picked up the box and tapped it gently. When bubbles arise on the surface, you know you’re good! These air bubbles will caused holes in the concrete when it cures if you don’t get them out.

Step 5. I placed my smaller box inside and filled around it with concrete. I had to hold it down with my hand so it didn’t rise up with the added concrete. To get the bubbles out, I pressed against the walls of the inner box.

Step 6. Concrete needs to cure over 5-7 days. In order to give my planters support during that time, I placed cinder blocks around the mold. I pushed them up around the walls to hold everything where I want to be. To support the inner box from caving in, I filled it with a bunch of rocks from my garden.

Some people suggest misting your concrete with a hose each day to prevent it from curing too fast. Since my molds were made from cardboard, I didn’t think I could do that. Instead, I covered it with a tarp and let it sit for 7 whole days.

Step 7. When the concrete had finally cured, I removed the tarp and cinder blocks. After ripped away the cardboard molds, I was surprised to see one turned out much better than the other. One had many holes from air bubbles I did not properly get out. 

Step 8. The next step was sanding all sides of the concrete with 60 grit sandpaper wrapped around a wood block. The one that cured with holes from air bubbles, I decided to use spackling compound to fix. This product is usually used on drywall, but it said it can be used on stucco which is similar to concrete. It also said it can be used in exterior applications if painted. I used a five in one tool to fill in all the holes.

Step 9. Before painting, I vacuumed up all my dust and debris!

Step 10. I spray painted my modern concrete planters with one of my favorite products, Rust-Oleum 2X Cover in the color Gloss Black. I sprayed multiple coats and also sprayed a couple polyurethane layers for protection.

Step 11. At this point, you could use a masonry bit to drill through the bottom for drainage. I didn’t have one, so instead I placed an inexpensive plastic pot with holes in the bottom inside my planter. Then I filled it with potting soil and planted my grass. I chose Karl Foerster because this tall grass will balance out the look of my short, blocky planters. Whenever I need to water, I can simply remove the plastic planters with drainage and fill in soil where needed.

Modern Concrete Planters

I think these modern concrete planters turned out beautifully and I can’t wait to flank my front door with them on our new front porch! Oh yeah, by the way, WE’RE MOVING! I thought I’d save this big news for last! We found a cute, old house in a nearby town that we are planning to renovate in the spring. I look forward to sharing all our room makeovers and home improvement help with you!

Thanks for reading! Until next time 🙂

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