Our Tennessee garden is built on rocks and clay. Instead of continually fighting the rocky hardpan, we decided to construct permanent raised beds and fill them with our own raised garden soil mix.
Behind our barn, we collect all soil that results from any excavations on our farm. One year we got lucky and scored a load of good soil from a neighbor who was renovating his farm pond. Almost all soil in our area includes rocks of one size or another, as well as lumps of hard clay.
Along with stockpiling soil, we make compost by combining stall bedding, coop litter, garden refuse, and kitchen scraps. Some things, like bones and shells, compost more slowly than others.
To fill a raised bed, we mix soil and compost together. For side dressing growing vegetables, we use compost alone. In either case, we needed a way to remove the lumps of clay, rocks, bones, and other objects we prefer not to incorporate into our raised bed soil.
Our solution was to construct a dirt sifter that fits on top of a garden cart. When the cart is filled with raised garden soil mix, we use our garden tractor to tow it from behind to the barn to our garden next to the house. The same principal may be used to sift soil into any garden cart.
Trial and Error
Our dirt sifter is now in its third version and we believe we finally have the design perfected — at least we haven’t come up with any new innovations in several years. Version 3 is constructed of half-inch hardware cloth, rebar, 2×4 lumber, and plywood and can be made any size to fit any type of garden cart.
An issue we encountered with our earlier dirt sifters was the angle of the screen. If it’s too steep, soil doesn’t fall through but instead rapidly rolls off onto the ground. If the angle is too shallow, too much elbow grease is needed to work soil through the screen. An angle of about 18 degrees proved to be ideal for sifting both compost and soil, while larger debris rolls down and falls off the bottom.
Another improvement incorporated into version 3 was solid sides, which let us pile more raised bed gardening soil into the cart than our previous open-side sifters allowed. Additionally, an apron at the front channels off stones and other debris that may otherwise pile up at the lower end of the sifter.
No More Sagging
The biggest problem we had with version 1 was sagging hardware cloth. In version 2, we solved that problem by reinforcing the hardware cloth with two lengths of rebar.
But the hardware cloth still didn’t hold up well, kept fraying, and needed to be frequently replaced. We solved that problem in version 3 by using American-made hardware cloth.
The only hardware cloth available in our local area is imported. Buying hardware cloth made in the USA, and having it shipped, is expensive, but well worth the cost. Compared to imported hardware cloth, the gauge is significantly thicker and the galvanizing is far superior. The result is big savings in both dollars and time not spent repairing the sifter.
Previously we had been replacing the hardware cloth at least once a year. Now, despite several seasons of heavy use, the version 3 sifter still has its original American-made hardware cloth, showing little sign of wear.
When conditions are perfect — meaning the soil or compost contains just the right amount of moisture to be fairly crumbly — one person working alone can handily use the dirt sifter. Under ideal conditions, a shovelful of soil or compost tossed onto the screen easily sifts through, while debris rolls off without any help.
When conditions are less than ideal, a second person makes the job go more smoothly. With the dirt sifter is positioned next to a pile of finished compost, one person shovels compost onto the dirt sifter while the other moves it up and down the screen with the back of a rake. Lumps, bones, stones, and other large pieces roll off the dirt sifter into a pile for disposal wherever clean fill might be needed. The resulting sifted compost is light and fluffy, making it the best compost for garden side dressing.
When we want raised garden soil mix, we position the dirt sifter between the soil pile and a pile of finished compost. Here an additional helper comes in handy, one to shovel compost, the other to shovel soil, while the third person works the rake against the screen.
Coming up with just the right proportion of soil to compost was a matter of experimentation that depends largely on the type of soil used. Initially, we tried half and half, and then one to three, but weren’t entirely happy with the results. Eventually, we came to the conclusion that with our heavy clay, two shovelfuls of soil to three of compost makes nice, loose soil that holds moisture without getting heavy, soggy, or lumpy — the perfect soil for raised bed gardening.