One of the Joys of Maturity
One Last Raised Garden Bed
Having constructed raised beds for all of our vegetable garden plots in our back yard over the last ten years, I had one last raised bed plan buzzing around in my head. I wanted to surround three sides of our shallow well cover with a rather narrow raised bed to be used as an herb garden.
This bed presented some challenges not faced in constructing the other beds. It was to be near a water source, which ruled out (for me, at least) using any kind of treated lumber for the construction. Also, the ground slopes away a good bit from one side of the well. And once I began digging trenches for the lumber to enclose the bed, I found the soil to be very heavy clay, possibly added to seal around the well when it was dug.
I had previously used six inch landscape timbers for our other raised beds, and that would have been my choice for this bed. But not wanting to use treated timbers, I chose to use cedar lumber which doesn't rot too quickly and has no added chemicals that might leach into the soil and well water. Cedar lumber is also terribly expensive, over twice to three times the cost of regular, pressure treated landscape timbers.
Building a table that had legs made of 4x4 cedar for a pitcher pump I installed over the well, I decided I could use 4x4s for the new raised bed. With some very good anchoring with rebar, the 4x4s should be able to withstand the outward pressure of the soil they will hold in.
The first thing I do in constructing a raised garden bed is to stake and string its perimeter, just like one would do when putting in a foundation for a house or garage. I measured twenty-one and a half inches out from the base of the well (not the well cover). That measurement allowed for the three and a half inch true width of the landscape timbers to be used and yielded an eighteen inch wide bed.
Staking and stringing involves using string to establish a straight line along, but slightly beyond the intended dimensions of the bed. That allowed me to have string crossed at the corners to accurately place the corner stakes. Hammering in stakes along the strings and at the corners of the intended bed laid out the perimeter for the bed's timbers.
Leaving the string in place, I then dug a trench for the first and longest timber on the low side of the well with a flat garden spade. I actually dug a couple of inches outside the timber's dimension to make leveling a bit easier. I then realized that I needed to dig out all of the initial trenches for the other timbers. As I did so, I kept stacking up timbers in the rough trenches to make sure the top of the bed would be slightly lower than the top of the shallow well.
Knowing that I'd later have to add extra timbers on the low side, I began laying the timbers on the high side of the well. I needed a couple of short lengths of timbers coming out from the sides of the well to establish the bed's 18 inch width. I carefully leveled the short bed, using mostly coarse builders' sand to achieve a level trench.
After hammering in some rebar to anchor the first short timber, I began working on the side trench of the bed. It quickly became obvious that the low corner of the bed would need to be three timbers deep.
I added a short, base timber at the low end of the bed, leveled the second timber, and hammered them home with rebar. (See Building a Raised Garden Bed for illustrations on using rebar to anchor landscape timbers.)
At this point in the construction, I knew I had planned correctly. Sometimes, one wonders if the whole thing will turn out to be a disaster. But I knew I had this down, as the rest was just a matter of measuring, leveling, and hammering.
The low corner of the bed required three deep timbers, The bottom timbers actually didn't run the full length of the bed, but were necessary. The corners of the bed were overlapped to add strength to the construction.
At that point, it was just more of the same laying the remaining timbers for the other sides.
One note I should add here is to always, always install landscape timbers at least two deep to prevent heaving from winter freezes and thaws. I cheated and didn't do that with our first raised bed and have experienced heaving and warping of the timbers.
Filling the Raised Bed
Having discovered that the soil around the well was some heavy, gray, clay soil, I had to dig out a good bit of it before filling the new raised bed with more fertile growing material. The heavy clay soil dug got spread around our cistern where erosion had begun to expose the top of the deep tank.
I used a heavy garden fork to work in some gypsum, sphagnum peat moss, and lime to the base of the new garden bed. Since the native soil around the well was pretty nasty clay, I backfilled the bed with commercial compost and garden soil, peat moss, and a good bit of our precious home produced compost.
I was rewarded with a bed that produced lots of herbs for table use and preserving. Since I planted several perennial herbs in the bed, I'm hoping that planting in upcoming seasons will be a matter of filling in where annual herbs and flowers grew.
This construction was a project I'd long wanted to do, but never got around to doing. Having finished constructing raised beds for all of our garden plots in the back yard, I finally got to complete this project. The newly plumbed shallow well provided water all summer, never running dry. The herb garden was a repeated source of joy when cooking, as it is just a few steps from our back door.
I'd had this construction roughed out on computer since 2014. Sadly, the diagrams on notepad paper I actually used to build the raised bed have been lost. I was, however, able to find the old computer diagram and update it with the correct dimensions and also add how I stacked the cedar timbers.
After purchasing expensive cut 22" lengths of steel rebar for most of our previous raised beds, I realized that buying 10' lengths of the stuff and cutting it myself with a hacksaw would be far cheaper. One doesn't have to cut all the way through the rebar, but can cut about two-thirds of the way through and snap it off.
I didn't show how we anchor our landscape timbers in this piece. Please refer to my previous column on building raised beds for how we use rebar to lock our landscape timbers in place.
Be very careful when purchasing compost. Joe Lamp'l tells in Killer Compost: It Happened to Us how he ruined his new raised beds by using composted horse manure fill that had herbicide carryover from the hay the horses ate.
I titled this piece, One Last Raised Bed, as I really don't plan on building any more raised beds. When I was done with the new bed, I was glad I'd used 4x4s instead of the much heavier treated 6x6s I've used in the past. With advancing years, I'm not as strong as I once was. The 4x4s were pretty easy to handle.
Our other raised beds include our first, that was actually a terrace to control soil erosion, but it got enclosed to be an enormous 16' x 24' raised bed. The next bed was enclosing our asparagus in a 52" x 16' bed, something that set back our asparagus harvest by a year or more. Then came two 4' x 16' garden beds, each of which is a joy to work from the edges (approximate interior dimenstions, 36" x 15').
A raised bed made of landscape timbers won't be for everyone. Here are some links to some good articles about building raised beds with timbers or 2" lumber:
From Steve Wood, the at Senior Gardening