I've seen similar sized planters on etsy go for $15 - 20 a piece. But you can make them on your own for a fraction of the cost. They're pretty simple to make, but it does take a bit of elbow grease to mix up the concrete and you will get a bit dirty.
For my molds, I used some cheap-o plastic containers from the dollar store. But if you want to be 'green', you could use old take out containers, clean ice cream or milk cartons, etc. Basically just something in a size you like. For the 'hole', I would suggest using a plastic disposable cup. I used old wine bottles for mine - but more on that later. There are some pros and cons to using glass.
For the concrete, I used a product called Countertop Mix (
http://www.quikrete.com/ProductLines/CountertopMix.asp). It has additives to make it more flowable. But since most big box home improvement stores probably don't carry this product, I would suggest using Sand Mix (
http://www.quikrete.com/ProductLines/SandToppingMix.asp) instead. And I believe the Sand Mix is available in smaller 10 pound bags. I found the 80 pound bags of the Countertop Mix a bit tedious to mix for a weakling such as myself. I also added some charcoal colored pigment to the concrete to darken it up a bit.
Before mixing up the concrete, you'll want to put some sort of release agent on your containers & cup, to make them easier to remove after the concrete has set up. I used WD-40. Just a light coat of WD-40 will do. If it's on too thick, it may stain your concrete.
Basically, just follow the directions on the bag on how to mix the concrete up and for how much water to add. It's always easiest to mix by adding the concrete to the water in small quantities vs. adding water to the concrete. With the Countertop Mix, mechanical mixing was required in order to activate the flowable additives. But since I didn't want to rent a concrete mixer for just 2 bags of concrete, I mixed by hand - which was a bit of a bad idea. The concrete ended up being too thick for me to mix so I had to add extra water. Typically adding extra water to concrete is bad because it weakens the concrete - but I figured since the concrete is just being used for planters, it probably not a huge deal. The ideal consistency is that of 'chunky oatmeal'. You definitely don't want the concrete to be soup-y.
Once your concrete has reached the desired consistency, pour it into your containers and push in the cup to make a hole for your plant. You may need to put some rocks in the cup to weigh it down and to prevent it from being pushed out. I used a margin trowel to help consolidate the concrete and to smooth off the top. You may also want to lightly tap on the sides of the container with a soft mallet or the handle of the trowel to help with the consolidation.
You'll want to store your concrete planters in an out of the way location for a few days while they cure. If it's hot, dry, or windy, you may want to mist them with water or cover them with a plastic baggy to keep the concrete from drying out too fast. After 3 - 4 days of curing, the concrete should be hard enough so that you can remove your forms. You will probably see a few pin holes on the sides of the planters from any air bubbles, despite the consolidation. I actually kind of like the way they look, but if you don't you could probably use some grout to fill in the pin holes or buff them out.
Since I used old wine bottles for my hole, the alkalies from the cement seeped through the protective layer of WD-40 and actually etched the surface of the wine bottle, permanently fastening the bottle to the concrete. Because of this, I wasn't able to remove the wine bottles. Instead, I carefully broke up the tops of the bottles with a hammer. This resulted in some jagged edges of the wine bottle inside the planter. The good thing is, I don't have to worry about sealing the inside of the planter. But I do have to be careful when planting my plants, so that I don't cut myself on the edges of the broken glass.
Since I had access to a wet polisher / grinder, I polished the tops of the planters to expose the aggregate. If you're extra crafty, you can add broken pieces of glass or those glass rocks from craft stores to the concrete, for a decorative look, granted you'll be polishing your planters. If you're not polishing the concrete, then don't bother with the glass aggregate, as you won't be able to see it without polishing.
If you didn't use glass for the hole, then you'll want to seal the planter with a waterproofing sealer for concrete, to prevent water from seeping through the porous concrete. Depending on the type of sealer you use, the concrete may need to cure for an additional 7 - 28 days. For some of the larger planters I made, I'm probably going to go with a siloxane penetrating sealer, that will keep the natural look of the concrete. But if you want a shiny look, that will also darken the color of the concrete, go with one of those wet look, high gloss sealers for concrete.
Since I'm going to be keeping some of my planters indoors and I don't want them scratching up any furniture or floors, I put some of those felt sticky pads for furniture underneath the planters. Or if you have any craft felt, you could cut it into the shape of the planter and glue it onto the bottom as well.
Now just add a succulent or cacti and enjoy your new planter!
