Starting a raised bed garden can be an expensive prospect. You can buy a ready made kit, many of them topping out well over $100 per bed. I make my own raised beds, read on to see how you can make a raised garden bed for under $30! It’s easy and doesn’t require any special equipment aside from a screwdriver and a saw.
I have several size beds in my garden, but I have found that 4 ft x 8 ft is a great size, enough to handle lots of plants, even bigger ones like tomatoes, corn, & sunflowers. The bonus with a 4×8 bed is there is no waste when you use 8 foot boards.
I use untreated pine boards. If you have the budget for it, cedar is the best choice as it will resist rot & insects better than pine. But it’s also very pricey. Depending on your climate you should be able to get 7-8 seasons out of the pine before needing to replace them. You can use most any wood, metal, plastic, stone.
The only wood I avoid is pressure treated lumber. You should never used old (pre 2004) pressure treated wood or railroad ties you might have salvaged. Before 2004 residential pressure treated wood was treated with chromated copper arsenate. CCA was known to leach arsenic into the soil & plants growing in that soil. Currently, pressure treated wood is treated with a cooper based treatment. Experts say the health effects of using this for a raised bed are minimal. Excess cooper can stunt plant growth however. I say better safe than sorry and just choose a different material (or alternately line the pressure treated wood with plastic).
For this DIY article I will be using 2×3 pine boards, but you can see in my garden that some of my beds are made of stacked 2x4s, some are stacked 2x3s, some are 2x12s. I try to use what I can find or what is on sale at the lumber yard. You want the final bed to be 10-12 inches deep.
First prepare the area where your bed will be. You can put down a layer of weed cloth to keep weeds from popping up in your bed. You can also put down a layer of cardboard to smother weeds underneath. At the very least, remove any grass or growth and loosen the soil.
12 pine boards 2 in x 3 in x 8 ft
2.5 inch or 3 inch screws (about 50)
scrap wood for supports (I used 2 in x 2 in boards)
plastic sheeting, weed cloth (optional)
Separate 4 of the pine boards and cut them in half, so now you will have (8) 4 ft boards and (8) full size 8 ft boards
Put two screws in each corner to build a rectangle with two 8 ft boards and two 4 ft boards
Make four of these rectangles
Stack the four rectangles where you want the garden bed to be, it’s ok if the boards are a bit warped and don’t line up fully.
Use a scrap wood brace in each corner and in the middle of each 8 foot side (this will stabilize the bed and bring all the boards into alignment)
I like to paint my beds with a high quality outdoor paint. Don’t paint the inside to avoid any contamination. Not only does it look cute, it will help protect the wood for longer life. Another optional step to help prolong the life of your bed is to line the wood on the inside of the bed with plastic sheeting. This will provide a barrier between the wood & moisture.
Filling your raised bed
This can be where the real cost comes in. If you are resourceful it doesn’t have to be though. If you have a large compost pile this can help, but this bed will require about 27 cubic feet of soil (or 1 cubic yard) to fill so you would need a really big compost pile to fill this.
Check with your local municipality or farm extension. Many towns offer free or low cost compost to it’s residents, although you often have to be able to transport it yourself. Before bringing free compost to your garden, ask if it is screened. If not, it could contain seeds and weeds that will take over your garden.
Local farms or garden centers will usually offer good quality compost and often can deliver it right to your house for a fee.
I would not recommend relying solely on topsoil or loam to fill your beds as it won’t provide the nutrients your plants need. With intensive gardening styles like square foot gardening your plants will require a lot of nutrition so using cheap soil will hurt you in the end with poor plant growth. A 50/50 mix of compost & topsoil is a great all purpose blend for general vegetable garden styles & perennial beds. For square foot gardening it is recommended you add equal parts compost, vermiculite (to aid in nutrient absorption), and peat moss (to help with moisture retention).
Bagged soil at garden centers is generally going to be cost prohibitive to fill a bed this size. To buy good quality bagged compost it could easily cost you $140 or more to fill this bed, where you could get a yard of compost delivered and support a local farm for $25-$30.