You know cinder blocks have a lot of advantages.
1. They are right at 8 inches high which makes one level a great height for a raised bed.
2. They are easy to find so if you need more most home improvement stores have them so adding on will always be easy.
3. While sort of ugly they are easy to paint and can be any color or look you desire, including dark colors to raise tempetures in cooler climates or light ones for warmer climates.
4. Affordable at 16 inches in length it would take about 18 to make a 4x8 bed. (often a very standard size) at 84 cents each you are talking 15 bucks a bed. Heck going to 16x4 and you are still a good bit under 30 bucks. The top soil will cost more then that!
5. And now the Jack Spirko bonus item,

. You know those holes! Fill them with dirt and plant smaller plants in them. That invasive mint for instance can be largely contained and you can add other herbs to attract beneficials, include some greens (beats, chard, etc) and even plant some marigolds, nasturtiums, etc to repel the bad guys. Garlic and onion are a natural in them as well, just go one in each hole and you can even get the repelling effect around your beans and peas from Onions and Garlic with out the negative effects of planting them in the same ground. Really cool huh?
Now can someone please explain to me why I used landscape timbers for my beds?
