Cover Crops: When Compost Just Ain't Cutting It Anymore

I don't know about you, but I constantly feel like I'm battling to get more nitrogen into my soil. I try to add compost to it from time to time, but my efforts to create compost don't seem to keep up with my garden's need for it. I also periodically add aged steer manure to the soil, but my daughter has made it well known that she doesn't appreciate being dragged along on the outings to buy cow poo.

My little angel

So I have been looking for a better solution, and I think I've found it: cover crops. As Mother Earth News says: "A cover crop is any plant grown for the primary purpose of improving the soil." I started looking at cover crops like legumes to add nitrogen to the soil, but it turns out that cover crops can do a lot more. They can deter weeds, aerate the soil, mulch the soil, bring up other nutrients from deep down, and--this should perk up the ears of all of you battling our Arizona clay--break up hard-packed soil.

Arizona soil can be a teensy bit tough to break up sometimes

I really like the sound of that last one too. I'm getting really tired of pulling out my tiller to break up the soil, and I'm starting to wonder if it's such a good idea anyway. The idea of having some plants break up the soil for me sounds so much nicer. (One of these days, I'll ramble on a bit about no-till gardening.)

Now the question is, which cover crops should I use? Well, not surprisingly, it turns out the best cover crops to use vary considerably depending on location, soil requirements, and time of year. In my case, I'll be planting my first cover crop in late July, after I'm done solarizing my soil. As part of the solarization process, I already tilled the soil, which means I don't have to worry about compaction. I really just need to add nitrogen to the soil. So I'll probably just use cowpeas, which are great for adding nitrogen and can withstand our brutal summers.

But what about you? What if you want to grow cover crops in your garden, but your circumstances are different than mine? How can you easily figure out what to grow?

Google returned about 6,340,000 results. You'll have this figured out in no time!

I recommend checking out this great chart from Peaceful Valley Farm and Garden Supply. I have read roughly a gazillion articles and books about cover crops, each with some of the information in this chart, but not all. This is the only place where I've seen it so nicely summarized all in one spot. (Peaceful Valley also sells a lot of the products mentioned in the chart. Again, they're the only site I've found that sells them all, which is nice.)

As I mentioned above, I'm no expert, but I have read enough about cover crops to make my eyes cross, so I'm going to go ahead and give you some advice on the subject. Here are a few things that seem to come up again and again in the articles and books that I have read:

• If you're like most gardeners, you should probably be cover cropping a lot more than you do. Get creative if you have to--plant quick growing cover crops between seasons or mingle cover crops with your regular plantings if necessary.
• When planting legume cover crops, use inoculant to speed up the nitrogen-fixing process unless the seed is already rhizocoated. (For the definition of terms like inoculant and rhizocoated, see What you need to know about our cover crop.)
• With most cover crops, you'll probably want to cut them down before they go to seed so they don't take over your garden. Common wisdom seems to be to mow down the crop when approximately 50% of it has gone to flower.
• Think carefully about what you're going to do with the crop when it comes time to mow it down. Are you going to till it in? Let it decompose in place? Throw it on the compost pile? What you choose controls how much nutrients the crop adds to the soil and how soon you can plant something else in the same spot. Check out green manure to learn about the various options.

That's pretty much the extent of my wisdom on the subject. I will let you know if I learn anything new though. To hear from some other Arizona gardeners who have used cover crops, I recommend: 

• Arizona Victory Garden - Cover Crops to Improve Arizona Soil (I miss the Arizona Victory Gardener. He doesn't publish any new blog posts. His old ones are great though.)
• Backyard Gardener - Plant a Cover Crop 
• Backyard Gardener - Growing Legumes to Improve Soil Nitrogen

Solarizing the Garden: The Upside to This Brutal Heat

In my last post, my garden was doing awesome. My tomatoes were out of control. I was constructing supports for green beans. Everything was thriving.

Work it! Oh yeah, you know you're looking good. 

And then, a familiar thing started happening. The heat hit and my plants started going down one by one in a blaze of glory. Does this sound familiar? Yup. It's the same thing I was whining about last summer. And just like last summer, at first, I just thought I had not planned properly for shade. But then I started seeing some posts on the Tucson Backyard Gardening Facebook group that started making me look closer at my plants.

The tomatoes and green beans were dying from the bottom up. The leaves were getting yellow. And here's what really got me thinking: they were developing brown spots along the leaves. That's not the look of a plant dying from heat. That's the look of a plant that's diseased.

Ewwwwwwwww 

I can't know for sure what my tomato plants and green bean plants had, but all signs pointed to fusarium wilt. (The only way to really know would be a lab test.) Looking back, it seems likely that a lot of my plants had fusarium wilt last summer too. So it seems pretty likely that the disease is living in my soil.

Ewwwwwwww.

That's the bad news. The good news is that our climate is perfect for treating the problem without chemicals. To get rid of fusarium wilt (and many other soilborne pests), you can cook 'em out using a method called solarization. (Doesn't "solarization" sound like it's custom-made for Arizona?) Solarization is a process where you lay plastic over the soil to concentrate the sun's heat to raise the soil's temperature. In cooler climates, people use the technique to start growing plants earlier in the season, when the weather is cold. In hotter climates, we can use the technique to bake nasty stuff like fusarium wilt out of the soil without using chemicals. Cool.

The process is pretty simple: Till the soil to loosen it up, smooth it out so the plastic can lay over it very evenly, soak the dirt really well, lay the plastic over it very tightly, and let the soil bake for 4-6 weeks. (Times will vary depending on the weather.) To get more details, I recommend this excellent article from UC Davis, a renowned agricultural school: Soil Solarization for Gardens & Landscapes.

Lucky for me, I don't have to solarize my whole garden (just most of it), so I do have a few zucchini and melon plants to hold me over while everything else bakes. Good thing, or I might go crazy with nothing to grow for a month and a half! I'll let you know how things go. In the meantime, happy gardening and stay cool.