A note from Edible Baja Arizona: In her article “Putting Down Roots” from the January/February 2017 issue of Edible Baja Arizona, Amy Belk thoroughly explained how to grow root vegetables in Southern Arizona. Here are her answers to a few gardening questions sent in by a fellow gardener and eBA reader.
“I understand there are few if any cover crops to plant during the summer months in the Phoenix (Surprise, AZ) area.”
There are a couple of cover crops that work well in the low desert and will take a substantial amount of heat, but I’m not sure how they would do in Surprise. I usually recommend a legume like Lablab purpurea or cowpea, as they can help fix nitrogen in the soil. Alfalfa is another good cover crop that should grow in Surprise, though it’s not a legume. Ask your county extension what they recommend as summer cover crops that don’t need much tending.
“…what would be the best way to add nitrogen to the garden (4′ x 40′) – raised bed adjacent to backyard wall – during the months of May through September, so that perhaps a cover crop could be planted early in fall for January- February garden planting?”
This is a tricky question, and you might get different answers from different experts. Nitrogen doesn’t stick around for very long in most soils (there are many things in the soil other than plants that use it up, and it can wash out of some soils fairly quickly, especially with frequent watering). I would think that just about anything you apply before your summer departure would be largely used up and/or washed away by the time you return, and the soil will be ready for a refresher in the fall whether you added nitrogen over the summer or not. That’s no problem, you can work fertilizer into the soil a week or so before planting in fall or in Jan, or you can use an organic product when you plant to add nitrogen. This option would be a lot less expensive and less labor intensive than growing (and watering) a cover crop.
“I was told to just put on a good manure and let it fallow over the summer months. Any suggestions or advice on this?”
I talked to several of my gardening friends (who I consider experts), and we all agreed that spreading manure wouldn’t be a bad idea, but it will likely be mostly broken down by the time you return, and you’ll need to add more nitrogen anyway. You could certainly try it and do a soil test when you return to see how much nitrogen is left…it would be interesting to hear how it works out. You might have better results from mixing in some good compost and mulching over the top of the bed before you leave…that way you’re at least improving the soil structure and supporting the microbes while you’re away, but you’ll probably still need to add nitrogen again in fall.