I've been preparing some new garden beds over the winter for planting this spring. The area being prepared consists of very hard compacted dirt, typical of Arizona desert soil. It has almost no organic material and was once used as a driveway. It has the consistency of concrete when dry, and wet concrete when wet.You will probably notice first of all that the beds are not the typical raised beds. After a lot of reading and a couple of years of experience, I think that sunken beds, not raised, are the most appropriate for this desert climate. Raised beds have advantages, especially in wetter, colder climates. They are easier to work (you don't have to bend as far), and they dry out and warm up quicker in the spring. It would be nice to not have to bend over so far to work them, but I definitely don't need any quicker drying or warming. Being sunken a couple of inches below the surrounding ground level has the advantage in this situation of holding on to any precious moisture in the soil for as long as possible and it also allows me to easily flood the whole bed and not have the water escape.
So how do I go about preparing a new garden bed? First I dig down about 18 inches to get through all the hard stuff. Besides the generally compacted dirt, in this particular location there is also a layer of clay go get through. It sounds like a lot of work, but it's really a lot harder than that! I use a pick axe or a huge steel bar with a chisel shaped end to break up the dirt, then shovel it out. It's probably overkill but this way I get down to where there is good drainage and the soil is loosened up deep enough for anything I want to grow. Besides, I only have to do it once. As I put the dirt back in the just excavated hole, I mix it with about 25% horse manure. I have an endless supply from a neighbor down the street for the hauling. I don't bother to compost it first since it's going to sit in the ground for a couple of months before I plant anything anyway. As you can imagine, there is plenty of dirt left over since I not only fluffed up what was there but I also don't fill the hole back up all the way and I replace a lot of the dirt with manure. I have to be imaginative to figure out what to do with all the extra dirt, like fill potholes in the driveway, fill in areas near the wash that have eroded over the years, etc.
Next comes amending the top 6 inches or so. I like to add a couple of applications of soil sulphur over a couple of months to try to get th PH lowered down to closer to 7.0 since the desert soils are quite alkaline. I also add an inch or so of more or less finished compost if I have it (I never have enough), some blood meal and some bone meal and maybe some rock dust. I will probably cover it with some straw ( or other) mulch while it waits for planting time.
All of that effort turns it from almost sterile desert dirt to just adequate garden soil. The first season it's not great soil, but if I keep after it for a couple of years, amending it some more every season and allowing the natural processes that occur under a layer of mulch it will turn out pretty good before too long.
The new beds pictured above will give me about 75 sq ft more area inside the cage for growing this spring. I have a couple more beds to dig, but they may not get done for this spring's planting. No hurry. This is gardening, after all....
