Green manure - special considerations for dry climates?

I’ve established a fair amount of comfrey, and always have a considerable amount of weeds, to use as a chop-and-drop style green manure. But I live in dry Colorado where these leaves tend to simply shrivel up dry as a top layer instead of becoming incorporated into the top soil through continued rain.

I’ve covered my yard in wood chips. The wood chips, as well as the adjacent pine forest littered with sticks, pine needles, and pine cones, disintegrated very slowly, even after months of time covered in snow in the winter. As soon as the snow melts the materials become and stay mostly bone dry and I’m wondering if this climate isn’t meant for the chop and drop style of layering other climates might find beneficial.

I know adding more and more wood chips in my yard would ultimately help retain moisture to acceptable levels. At this time I don’t have a tractor to eat in this process of accumulating and spreading them.

I still have a pile of wood chips that I continue to add green manure to but even that is a painstaking process of covering and layering with brown wood material.

Should I expect different results from my dry climate then I would with a wet climate?  Should I approach the use of green manure differently—especially in regards to a chop and drop method of layering?

I’ve covered my yard in wood chips. The wood chips, as well as the adjacent pine forest littered with sticks, pine needles, and pine cones, disintegrated very slowly, even after months of time covered in snow in the winter. As soon as the snow melts the materials become and stay mostly bone dry and I’m wondering if this climate isn’t meant for the chop and drop style of layering other climates might find beneficial.

Living in dry New Mexico, your observations resonate with my experience. To deal with the lack of decomposition and extreme desiccation in sun exposed areas, I am limiting my layering strategy (browns-greens-browns-greens…) to plant drip lines only. Instead of the whole yard, I apply thick layers of browns-greens in a ring around the tree at the shady drip line. Then I water the carbon-rich-chips and green manure layers at the drip line to keep the composting process active.
This diagram from Denver Water shows that the most efficient way to water a tree is to water at the drip line. By placing the green plant waste and carbon at the drip line the compost stays moist and the tree gets the water and nutrients it needs. As the tree (or shrub) grows, continue composting and water further outward at the drip line. Leave the old mulch under the canopy. When planting understory plants beneath the canopy, pull back that top layer and find gorgeous humus rich soil.

Amy Gardener wrote: To deal with the lack of decomposition and extreme desiccation in sun exposed areas, I am limiting my layering strategy (browns-greens-browns-greens…) to plant drip lines only...

Interesting strategy!  Thank you so much for sharing your experience and wisdom!  

Do you also water on top of the piles you create?  Or does the drip line underneath contribute enough water through evaporation (or other) to reach these layers on top?  Or maybe you put the drip line loosely on top of the pile?

Unfortunately my trees are just saplings at the moment, but I'll keep this in mind when they get bigger.  Until then I assume my concern is valid and maybe I should focus on creating humus through compost piles I frequently water.

Sapling stage is the ideal time to start, S. Marshal!  Just keep your starting compost ring at least a foot away from the young trunk so the moisture won’t cause mold, fungus or rot to develop at the fragile sapling trunk or graft crown. Start your sheet composting with an opening in the middle (like a donut) for the trunk. You may not have shade yet but the ringed pile a foot away will be the place to water so that the sapling roots reach outward instead of forming a tight ball beneath the little tree. The tree roots will find their way to the nutrient-rich “tea” below the ring of compost.
The term “drip line” means the line of water (ring) that drops from the outermost silhouette of the tree. Imagine the leaves repelling water like an umbrella so the rain drops on the ground in a circle. That’s the tree’s drip line (not an irrigation hose drip line). Good luck with this focused (and easier) approach to building soil and retaining moisture.

Dry summer climates definitely do call for different methods.  My climate has no rain from mid-May through sometimes mid-December, and I've had to customize methods.  I used to use mowed weeds, but they just created too many more weeds, so I compost those now.

Wood chips are excellent for holding moisture, even when you think the climate is too dry.  I don't think you can go wrong with them, unless they are from trees that have growth inhibitors, like redwood and red cedar.  Even those just take longer and are better than nothing.

You might experiment with just how thick a layer works for your soil and your location.  It might be more than you think, 3", 4"?  Check for how moist the soil is underneath as you add them, you ought to start seeing damp soil and maybe white fungi.  Then maintain this thickness as they will incorporate with the top layer of the soil, and you want to keep the soil covered completely.  If there is the occasional downpour or drizzle thick woodchips will keep and hold that moisture to the soil.  

If the wood chips are from very green wood it's going to take longer for the soil critters to be able to use what they have to offer, so adding nitrogen from composted manure helps, pulling the chips back and watering in about a 2" layer, then replacing the chips.  Urine also has nitrogen, and can be diluted 1:1 and added to the soil under the chips, but don't get urine on plants or annual plant roots.  Out around the drip line of trees, mature perennials, grapes, berries, etc. is okay.

As far as green manure, I've found it easier to stick with deciduous food shrubs and trees that drop their leaves planted in food forest style.  Ground covers like native vetches are great, just let some of them go until you get seeds for next year.  Mow or clip them off, leaving the roots in the soil and the nitrogen nodules they have will also improve soil.

Trailing Nasturtiums (there are some that are mounding, but aren't as helpful,) are cheerful annuals that will spread and create shade.  They die back and disappear, easy to save seeds from.  If you have animals I wouldn't recommend burr clover, burrs can get into ears and noses and cause problems, but I've got a lot of it showing up in general.  I mow it when it gets about shin height, and it grows back in late spring, before it dies back and reseeds.

Native annual grasses are also excellent.  In Africa they have now found that allowing the annual native grasses to grow holds water in the soil and the roots break down to improve soil.  Mow them after they have gone to seed, and leave the roots in the ground.

If it's a new batch of chips on soil that's never had wood chips, filling in between with bagged tiny chipped wood mulch from the nursery can help kickstart things.  I've even gotten some mushrooms showing up from the bagged stuff (in the greenhouse, that's how I know it's not my mushrooms.)  Mushrooms are always a good sign.  Let them grow and complete their cycle so the spores will overwinter.  They say mushrooms are more creatures than plants, so be nice to your mushrooms :-)

Hugel trenches, a couple shovel blades deep, with very dead wood, also hold the moisture and create great growing environments.  I fill in around the wood with native soil and manure, composted or not, watering it all in.  Then put really rotted, pithy wood that you can twist with your hands, at about the 6" level (hand depth) so it will absorb water with nutrients and the roots can penetrate that pithy wood, and take advantage of what it has absorbed.  Topping it off with compost and woodchip mulch.  These have worked the best for me in general, and will last for several years if woodchips are added and break down, migrating down into the soil.

@Cristo Balete

Thanks for your long detailed reply!  I'll give those ideas a try!

Something else that I've seen a lot of in the food forest videos is sweet potato vines.  You've probably got a short growing season, but the vines grow quickly and cover the ground, creating shade and providing biomass.   There are lots of videos on YouTube about how to start sweet potato vines, but basically you set the tip of one in water and when the shoots that come off it get about 6" you detach it, then put it in a 4" pot and get a good rooting on it, then plant it.  Sweet potatoes take a really long time to form, so you may not get any before the ground freezes, but it is a good ground cover.

Another popular mix is field peas and oats.  There are a couple seed companies that have the larger packages of this mix.   The traditional idea is to till them in when they are done, but I am not a tiller,  I clip off peas, leaving the roots with nitrogen nodules in the soil, and the oats will die back, their roots will rot and improve the soil as well.

If you don't have the time or inclination to do a deeper hugel trench, even one shovel depth is good, with smaller dead branches and shrub clippings, filled in as described above.  Even if the roots can't get into the wood in the first couple years, they can be around the wood that is holding good microbiology on the exterior.

Here is not strictly dry, winter and spring are usually beautiful, but our mediterranean summers are akin to desert climates: scorchy hot and draugh. Little to no irrigation.

My strategy for mulching goes like this:
Pruned big branches go buried under the beds in the hope that they find some extra moisture there. Pruned small branches and leafs go around tree trunks, hoping that the shade provide some extra moisture. Wood chips are insanely expensive, so not an option.
Weed cuttings go over the vegetable beds. They become ashes under the sun and our veggies die anyways...

Cristo Balete wrote:Something else that I've seen a lot of in the food forest videos is sweet potato vines.

This is an excellent idea. I've started keeping my sweet potato vines on the ground in winter (our dry season- stays warm and occasionally dips to 0C or below), even if you get no potatoes the young leaves are great eating and if you have rabbits, it's one of their favorite fodder crops. As Cristo said, it's so easy to propagate them and costs next to nothing, and they're pretty resilient.

For starting sweet potatoes at home, I find that cutting the end of the sweet potato that sits in the water makes it produce slips much faster (by weeks if not months).  They make lovely houseplants also, so if there's a variety you really like you can just keep a potted plant and take cuttings for the vegetable garden each year.  

My dad had a story about the sweet potato at his work.   Apparently one of his coworkers stuck a chunk of sweet potato into the breakroom tree and for many years both plants lived there together in the breakroom

Hi S, I have your same problem and I have had your very same question for some time now. I've just recently done a ton of research about it. If you watch this 8 minute Geoff Lawton video about Greening the Desert at the very end he shows you that he dumps a big pile of finished compost on top of the chop and drop.  https://www.greeningthedesertproject.org/humans-have-the-potential-to-turn-deserts-into-a-green-oasis/  He failed to mention this important point  in his 'Chop and Drop' videos!

O.K. maybe I'm wrong. Perhaps he is saying that he is going to 'chop and drop' on top of the compost. But I have the same problem that you do. All my 'chop and drop' will just sit there in the hot sun bone dry until it turns to dust and blows away. Anyway, I hope this helps.