Making your own planters is easier than you think.
Serene, modern, and beautiful don’t seem like words that go with “concrete,” but fine concrete mixes are the favorites of artisans across the country. You can make planters for your patio, steps and walkways for just a few dollars, some patience and a bit of creativity.
Mixes
The secret to good concrete is all in the mix. The formula of sand, additives (chemicals) and aggregate (rocks, etc.) is what makes any concrete mix different from the other.
To make your planters, look for a fine sand mix. Artisans opt for special mixes that produce fine-textured products. Sakrete’s ShapeCrete is a clay-like concrete an artist can mold and cures after 24 hours. Molding ShapeCrete concrete over baskets, draped towels, bowls, etc. is much like playing with Play-Doh. Just knead and spread. Leave for 24 hours to harden. Buddy Rhodes Artisan Concrete Mix is a popular concrete mix for smaller craft projects. The mix is made up of fine sand and cures to an off-white color. Joann Fabrics has a Makers Mix that easily molds into jewelry or smaller planter projects. Any mix you can get at the home and garden store will work, but look for “fine sand” or “artisan” labels.
Molds
If this is your first time working with concrete, don’t worry; It’s pretty straightforward. Find a container you can toss, like an old milk jug, cleaned and cut with a wide mouth on top. Follow the directions on the mix bag, but in general concrete is mixed with 1 part water and 4 parts mix. Always add water a little bit at a time, continually stirring until the mixture has a toothpaste-like consistency. Then it’ll be ready to pour.
Recyclable materials are great to use for molds. Half of an orange juice carton will work for a small, tabletop planter. Pour the concrete mixture in about half way. Place a plastic cup in the container and push down. Fill the cups with weights like pennies or stones so the cup doesn’t float upward as the planter hardens. Fill the orange juice container the rest of the way with concrete. Using a trowel, level off the edges. When your project is dry (after at least 24 hours), remove the cup and peel off the orange juice container.
If you are using bowls or other objects you want to keep, spray them with a releasing agent before they come in contact with the concrete. A light spray should be sufficient. You can use vegetable oils or purchase a releasing agent to apply to the surfaces of your molds. Just about any vessel or shape can work as a concrete mold. Be sure to clean your molds immediately after freeing your concrete work of art.
Drainage holes are usually a must for all planters. Concrete is porous, so some water will seep through it, but the seeping may be too slow of a process for your plants. Masonry bits will drill concrete. Start with a small bit and work up to larger bits. One hole in the bottom of the planter should be sufficient. Larger planters may need several drainage holes.
You can also make a drainage hole in your mold. Roll a thin-width, long strip of cardboard into a small cylinder. Tape it closed so it remains in the cylinder shape. Firmly glue the cardboard cylinder to the bottom of your mold. When you press the smaller cup into the mold, make sure it sinks into the concrete enough to touch the cardboard cylinder. Add 
extra rocks for weight to keep it in contact with it. The concrete mix may still seep in between the cup and the drainage hole but it will be a thin layer that is more easily drilled.
Another trick to make drainage holes in molds is to use carrots. Carrots are stiff, organic material that will maintain the form while the concrete dries and can be easily removed after the concrete sets. Poke through your inner vessel and insert the carrots. Before pouring the concrete, set the inner vessel with its carrot “legs” into the larger mold. Carefully pour in the concrete, tapping the sides occasionally so the concrete settles in completely. (See graphic). Once the concrete sets, remove the inner vessel and carrots. Any residual carrot parts will biodegrade. The space in the concrete left by the carrots will provide sufficient drainage for the planter’s vegetation.
Surface Voids
Surface voids are the holes or pock marks that form on the surface of the concrete. Using the finest sand concrete mix you can afford can help avoid these marks. Some surface voids are inevitable unless you are a professional with a vibrating curing surface and other advanced supplies. The markings are unique and add to the piece’s rustic or modern aesthetic. If you want to cover the voids, you can purchase a slurry to spread over the surface. Painting over the voids make them less noticeable. Acrylic or latex paint also adds a way to incorporate the planters into the decor in your outdoor room.
Planting
Once you have your cute planters, it’s time for plants, right? Not so fast. You may want to let those planters chill outside for a few days and experience some rain. Lime in the mix may affect certain plants by making the soil too alkaline in pH balance. The amount of lime is probably not significant enough to truly impact the plants but a few days’ patience is probably worth the trouble, especially if you’re a novice grower and aren’t familiar with your plants or how to balance the pH levels of alkaline soil.
Concrete can weather the elements, but know that soil will expand when it freezes. This expansion can cause pressure on the sides of the planter and cause cracks. Move your planters in for the winter or empty them of soil to prevent winter splintering.