I have built a very large (5000+ square foot) annual vegetable garden for a community farm. I used sheet mulch predominately. However, I soon found that this had drawbacks. The cardboard cut off access to lower layers of soil, which were pretty concrete like anyway. The top layer of mulch absorbed, and then evaporated, a huge amount of water. Since the site has no automatic watering system, hours of hand watering were spent, to no avail. Similarly, light rains didn't do any good at all.
So it is time to rethink things. I am going to be building an experimental bed, to see if I can create a garden which only needs a little water once a week, even when the plants are small.
I will dig out a square bed, about four feet by four feet, and set aside the topsoil/ sod. Then I will use the subsoil to build raised mounds/ paths in a square around the pit I have created. In the pit I will build a hugelkulture with logs and sticks. I will mix the topsoil with manure and place it on top. Now I have a sunken waffle hugel. I will then add a thin layer of wood chip mulch. Over this, I will lay a layer of rocks from the hole. (There will be plenty.) The rocks will keep the soil surface cool and moist, while counteracting the cool nights here. Between the rocks, I will sink some ollas of various sorts; a single clay pot with a saucer on top; a five gallon bucket with a pinhole; a five gallon bucket with a small clay pot siliconed into the bottom of it; and various recycled containers. I will see which olla style works best for me. The regulated flow of a traditional olla may not be as necessary in my climate, since the soil could always use some water. To plant seeds, I will move aside the wood chip mulch around the stones, and push the seeds into the soil layer. Then I will add a thick layer of sand, which should allow water from irrigation or rain to swiftly flow down to the seeds, while stoping evaporation. The seeds will also be able to be planted much deeper then would be otherwise possible. Finally, a layer of leafy brush will be spread over the bed to deflect the sun till the seeds are up.
The rocks and sand might make it harder to add organic matter, but I think the hugel will make up for that. Every few years I can move the rocks, add some more sticks and manure, and replace the rocks and sand.
What do you all think?
One thing I will not be adding to this bed, but will be adding in the future if this bed succeeds, is some biochar in the hugel part.
Gilbert, I mentioned a couple things about my experience with a little of this in the other thread this was mentioned in, but I'll do a quick summary plus a little additional here.
In terms of water sinking in, the rock and sand mulch was great. The ground stayed damp for a significantly longer time underneath, so that was a huge plus. It also had the unexpected benefit, when it came to rock, of preventing smaller critters from digging in to get things.
However, it also increased the reflected heat of the area. Not a problem for the cooler months of the year, but it was enough to damage plants when it got very hot. HOWEVER, this is simply for my area, which turns out to be about 10-15 F hotter, on average, than areas where rock or sand mulch was traditionally used (3 growing months of average temps over 95F, where I am).
In areas where I had shade, however, this problem did not occur. That included areas which had enough growth to cover the ground OVER the sand or rock (like squash) by the time the heat started to increase.
Re: the leaves on sand. This is something I've tried too (a little organic matter on top of the sand). The one challenge has been the wind. With dirt, some of the mulch on top would usually mix in a bit during watering and so have something to adhere to, but this doesn't happen with the sand. So unless it was piled on heavily like a mulch, most organic matter on the sand just blew right off whenever there was a good wind. I thought this wouldn't be a problem for the waffle garden but I ended up right in a kind of wind eddy and it still happened frequently unless I got a few rocks on top of that to weigh them down.
I'm really curious to hear how your garden experiment works, Gilbert. What's the average hot temperatures where you are? Do you think you'll have some extra challenges with that or are you in an area that's more in line with the temps of places where this was done in the past?
Thanks for your reply! It really helps to hear from someone who has actual experience with a method.
July is the hottest month in Denver. The average high temperature during this month is 88, and the average low temperature is 56. A high desert climate. So I am hoping the heat will actually be an advantage, especially for melons, peppers, tomatoes, and eggplant, which dislike the cool nights.
I ran into a bit of a hitch already; the ground is so compacted and full of rocks that a pickax does not make much impression. We may be renting a mini excavator for some projects, and this will be added to the list. I will try to remember to keep this thread updated.