Sunday, May 16, 2010

Turning Grass into Soil

I have had discussions with a number of people in the last couple of months that are starting to put in new vegetable gardens. These are often people that are looking to replace their lawn and many of them asked me what I did to replace my lawn. I used sheet mulch, a permaculture technique that starts by placing cardboard or up to 40 sheets thick of newspaper on top of the ground followed by 12-18 inches of mulch. I was able to get several truck loads of wood chips and trimmings combined, about 70 cubic yards of material, delivered to me for free from the people that trim trees away from power lines. The chips are steaming hot from composting just a few hours after the chipper blows them into the back of the truck. I followed that later with manure and other materials to start turning the chips into soil. As the sheet mulch decomposed in the seasons that followed I started digging down with a garden fork and working and lifting the soil layers below that into the decomposing chips by pushing a digging fork as deep as it would go and just pulling back on the handle to make the soil deeper and the compacted layer disappear. Now when I dig where we had chips I cannot find a distinct soil layer no matter how deep I dig in with a fork.

If you are killing grass then how much material you use depends on what kind of grass you have. If it is grass that has a rhizome that runs under the ground then 6 layers of paper and some compost will just make it grow and spread even faster. Deep mulch and thick layers of paper are effective at killing almost anything as long as the paper is put down overlapping, the mulch on top is heavy enough, you protect your edges from invasive runners, and enough time has been allowed for the rhizomes to die and rot away. This takes at least six months to destroy perennial root systems but maybe longer. As long as you don’t dig through the paper layer you should be good. Even if your weed survives that, it will be much easier to remove because your soil will be soft enough to make it very easy to work. I still have a few stray roots but I can pull foot long pieces of grass root at a time without tearing them now.

The quality of the implementation is certainly more important than the quantity if you have a challenging situation like invasive weeds that are difficult to control. Just about the only thing that I consider to be a weed is lawn grass but I would also include things like the non-fruiting passion flower that has crept its way into several adjoining flower and vegetable beds. Try doing a manageable section at a time and keep the margins clean of any running root systems. Start small and see if you think you can manage another section after you have proven the concept of your implementation six or more months later. Cover it with mulch or compostable material, not finished compost or nursery soil mixes and make it deep. I have done 12-18 inches of just wood chips that I got for free.

Be prepared to wait. There is an obsession in the U. S. for instant results and instant gratification. Your choice generally speaking is this-naturally nutrient rich, deep, highly organic soil that you will take 9-18 months to build using mostly raw materials, or a poor to mediocre product that you bought and installed in an afternoon or a few days. You will be able to plant into mulch beds within 3-6 months with my method, just in time for a winter garden which should be planted starting in August.

I tried the recent fad of container gardening, square foot gardening, etc. some years ago and found that it created more problems than it solves. Containers require a large initial investment, break up the yard into illogical and more difficult to manage units, lower productivity, create inefficiencies to maintain, water, fertilize, harvest, and weed, and creates habitat for a lot of different pests. This might be a good method in some parts of the country but I strongly advise against it in the Pacific Northwest. It also falls into the category of trying to solve a problem by buying a manufactured product, a grossly inferior product to growing healthy soil with an active soil food web. In my opinion in this area, container gardening of any type should be a method of last resort for people that have no access to soil. If you are interested in nutritionally dense organic vegetables in a sustainable manner, then growing vegetables in containers can’t get you there. It is far harder to maintain container mixes than it is soil, requires continuous outside inputs to keep it going, and soil mix will never be a part of an active living soil community which can contribute to make organically grown vegetables have the highest potential quality without constant additional inputs. Soil mix will never become a humic soil which is what I consider the gold standard for soils. For the price of maintaining any kind of container garden, it is probably cheaper to give people money to go to Whole Foods market to buy food there than it is to grow it in a container. I consider this to be a method that should only be used by hobby gardeners or as an amusement, not a serious or economical way to provide needed nutrition.

If what I am suggesting above seems unattainable or lacking in detail, as an alternative to growing in boxes or containers I recommend picking up a copy of "Lasagna Gardening" by Patricia Lanza if you want to colonize your front yard with a vegetable garden and start growing this year. She has a really good, low work method for colonizing lawns and turning them into highly productive gardens by putting layers of mulch down and goes through all of the stages of how to make that productive in as short a time as possible. This is derivative of sheet mulching and goes into some detail about materials you can use, how to use different plants with this method and a lot of tips and time savers you might find useful. This is also a good way to manage a seasonally fallow bed that you want to prepare for next year or the next season. You should be able to find this book in your library. I also have a link to it on the side bar if you want your own copy.

Regardless of your soil type, the best thing you can do for poor soil is to add lots of organic matter, not finished compost or soil mix that is based on finished compost. Finished compost is useful as a quick fertilizer. You can also use it as a temporary building material if applied thickly enough because it packs and become anaerobic so can last up to a couple of years on top of the soil. It disappears quickly when mixed in soils but doesn't help the soil structure. Over time, soil mixes have a tendency to become heavy, anaerobic, and drain poorly unless it incorporates a long fiber organic material like peat. It is also possible to have too much organic matter in soil and not enough of a mineral component which is why deep mulch methods are most productive once you start mixing underlying soil with your mulch or plants have the ability to reach down and start interacting with more of the soil/mulch complex.

That is one of the reasons manure can be so valuable. It has a mixed texture with lots of woody material that takes a while to break down. It contains a wide array of micronutrients and expands the number of types of micro-organisms in the soil that contribute to higher available fertility, tie up nitrates and carbon then slowly releases it back to plants through the soil food web. The PAN, plant available nitrogen, of manure (except chicken manure) is only about 10% of total nitrogen after 60 days according to Oregon State University. So putting enough manure down to meet your nitrogen needs might mean that you are putting down too much phosphorous which could tie up other nutrients. Manure can also contain hormones and antibiotics unless it comes from an organic operation or someone you know that hasn’t used such things. Even when doing something as seemingly innocuous as building your soil you can’t be too careful about where you source your material from. The thought process that it is safe and reliable to buy everything you need is something that should be approached with some caution.

I prefer material like tree chips to colonize new areas because it usually has a low cost-free, is unlikely to have weed seeds, pests, or disease that affect vegetables because it is made from completely different plant types, and it just went through a chipper. I don't think there are any insects that can survive that. Other sources of compost could be rotten hay bales or other feed stocks that can’t be fed to animals that are often seen at the edge of fields. One of the reasons to develop a system that is self reliant, besides avoiding an ongoing expense of purchasing stuff to make it work, is that the more dependent you are on outside resources the higher the chances are that you will get some exotic pest or disease that will become a lifelong companion. I think it is OK to take some extraordinary steps to get a yard established but you should develop a plan and implement it as soon as possible how you are going to make this a closed system with the lowest need possible for outside inputs. This will save you money, lower your exposure to industrial chemicals and pest problems, and hopefully result in soil and produce that you know is superior in many ways that might not be obvious to a casual observer.

Tom Gibson