We’re not doing really tall beds - just eight inches. It’s primarily because our soil is such heavy clay that we want to be able to dump six inches of good soil on top of what’s existing so our plants can actually grow.
Should we get pressure-treated boards, or pine, or “whitewood” (which was described as spruce/fir) for our beds? We don’t plan on staying in our current house forever - maybe another five years. So it doesn’t have to last a lifetime. Thanks!
Ground contact is tough on wood, which is why there are treated boards such as pressure treated specifically approved for ground contact (see end label) and some ‘rail road ties’ for landscaping which are dip treated I believe, of a heavier gauge and also ‘approved’ for ground contact.
If you’re planning on eating what you grow in those beds, I wouldn’t use pressure-treated or railroad ties. Just use what’s cheapest – 2 x 10s framing lumber (typically spruce) from the home center. They’ll rot over time, but a little rot won’t hurt anything – on the contrary! They should last five years like that.
Does Pressure-Treated Wood Belong in Your Garden? The article should answer all of your questions.
If you can get it cypress is the way to go. Naturally rot resistant.
Pressure treated usually means arsenic. Avoid that and pick a natural answer like redwood.
Cypress, cedar, or redwood would all be ideal. Railroad ties are coated with creosote.
That being said, I used non-arsenic pressure treated for mine.
Another option to consider is cinderblocks
Just note that those other woods will cost you a fortune. A 2 x 10 x 12 for framing is around $15, give or take.
Look into “lumber” made from recycled plastic. “This Old House Answers” did a segment where they built a partially raised bed on a slope (so the bed was level) using that stuff. Pretty sure it costs more than wood, but not sure how much more.
I built beds in our yard using cedar. Another trick is to buy some plastic sheeting from HomeDepot and staple that to the inside of the boards. Just 0.2 mil thick visqueen which costs about $10 for 50 square feet should be fine. Properly balanced garden soil is really hard on wood and will cause it to rot faster than just a board sitting in dirt. The guys at the cedar lumber yard said using the plastic sheet can almost double the life-span of the wood. Basically, staple it to the inside of the board where it will be contacting the garden soil, and leave a little bit extra hanging down that you can wrap under the bottom edge of the board where it sits on top of the dirt.
Lots of good advice here. I’ll add that you do your beds a great service in clay soil by tilling/breaking the soil up before you add topsoil. Clay is rather impermeable; if you just dump the topsoil on top, you have drainage problems. Breaking the clay up encourages the better topsoil to integrate, and, then, the plant roots have a greater ability to further work the soil and make a good bed. A bit of work on the front end here is worth three times the effort later.
Cedar is also a good choice, long lasting, anti fungal, and ages nicely.
FML
Not any more, at least in the States. Facing the possibility of a consumer backlash and EPA restrictions, the lumber industries more or less phased out chromated copper arsenate (CCA) and went to other preservatives, most notably alkaline copper quaternary (ACQ).
Persoanlly, I like the idea of using sheet plastic to protect the wood from the garden.
Elm is also pretty good.
Apparently, wooden railway sleepers are now being made of untreated Azobe - an African wood that is quite resistant to rot all by itself - sounds like this would be a good choice. Not sure about the sustainability of supply though.
So is gaboon ebony, if it comes to that.
Unfortunately that has never grown in the UK or the USA
I have personal experience on this one. I HAD to built some raised beds really quickly once to put some “free if you get them RIGHT NOW” transplants. All I had access to were some untreated 2x4s, just regular framing timber, which had already been lying out in the weather in a pile for 5 years since the house I live in was built. That was almost 4 years ago and the beds are still holding together, and are still serving as my temporary moving plants about beds. Based on their condition, I don’t expect but maybe one more year out of them. So it will do in a pinch.
I’d never use treated for any kind of raised bed.
-rainy