Double Digging for Garden Beds

[Zee-Man]

@MnCanary Asked, in another thread, about my experience with double digging. For those who don't know, double digging is a technique to enrich the soil. Over time, nutrients filter to the deeper horizons in the soil. The very top layer is the O horizon; O for Organic. It is followed by the A horizon (A for ...well, A) Which is what is commonly called top soil. The next is the B horizon, where many minerals lie. And then the C horizon which is usually the clay pan.

 

[Zee-Man]

The idea behind double digging is to rotate the the O and A horizons with the B horizon. Clay is needed to provide negative ions so the roots (having a positive charge) can take up water and nutrients. The bulk of plant roots will be found in the top several inches of the soil with only tap roots reaching deeper.

Organic matter is what holds water. Leaving it on the surface means water is not held for the plants. Rotating it deeper means less need for watering and improved drought tolerance. This principle is also used in hugelculture. Pictured is the base of hugelculture.

 

[Zee-Man]

My soil is about 1/3 stone. So double digging serves another purpose; to make the tilth much more fine. The process begins by removing the top 6 inches of soils, the O and A horizon. The grass plants are sifted out and reserved. The soil is removed and reserved for later use.

 

[Zee-Man]

Next the B horizon is dug up, sifted and reserved. I'll go down to about 12 to 14 inches deep, or as far as I can wallow my tiller in, twice. The grass plants are tossed in the hole. The next row is then scalped, and sifted. Grass plants go in the pervious hole. Then the top soil is put in the hole on top of them.

 

[Zee-Man]

The B hoizon is once more dug up and sifted. It gets leaf mold and compost added and mixed in. Then it goes on top of the previous stretch. That process gets repeated until the end of the garden bed is reached. At the end the reserved top soil gets put in the hole followed by the reserved B horizon with leaf mold and compost..

 

[Zee-Man]

Here is a good illustration of why double digging is effective. The first picture is Sudex planted in unimproved soil. The second is Sudex that was planted the same day in double dug garden bed. They are after about 3 weeks of growth. At present the unimproved plot is about 24 inch tall. The double dug is nearly harvested for the first time (third picture). Sudex grows to over 6 feet tall! The first cuts from the double dug are already back to 3 feet tall heading for the second harvest which will be laid up as hay.

 

[tambayo]

I learned you feed the worms from above, just like grazing animals would and the trees do by feeding themselves from their own fallen leaves. Double digging just like plowing destroys all kinds of symbioses in the soil that create the network that supports all living things in it.
This method of agriculture (plowing and monoculture) is now even critized by UN reports about soil fertility.
That along with actively sterilizing soil like in artificial growing mediums for seed production even creates plants that no longer can tap in to that network (they lost the communication traits for it) and therefore are way more impacted by drought. Because they cannot like trees do trade sugars for water with the fungi networks that can grow long enough to reach the groundwater table. There is a reason perennials take longer to get started, growing enough rootmass and relationships takes time. Annuals need to do it all in one growing season.
You are promoting a lot of hard work that actually do more damage that good for what you want to achieve.

 

[Heartbased Homestead]

I learned you feed the worms from above, just like grazing animals would and the trees do by feeding themselves from their own fallen leaves. Double digging just like plowing destroys all kinds of symbioses in the soil that create the network that supports all living things in it.
This method of agriculture (plowing and monoculture) is now even critized by UN reports about soil fertility.
That along with actively sterilizing soil like in artificial growing mediums for seed production even creates plants that no longer can tap in to that network (they lost the communication traits for it) and therefore are way more impacted by drought. Because they cannot like trees do trade sugars for water with the fungi networks that can grow long enough to reach the groundwater table. There is a reason perennials take longer to get started, growing enough rootmass and relationships takes time. Annuals need to do it all in one growing season.
You are promoting a lot of hard work that actually do more damage that good for what you want to achieve.

I also subscribe to the benefits of no till, and am committed to the longterm development of microbial soil health. I also have seen many no-till farmers advocate for a 1-time tillage on the first growing season of poor land (like Zee-Man's rocky/clay/impacted), before moving on to permentant no till. It is a lot of work, and I appreciate you adding this caveat, but it might be necessary in some situations when we don't have 2-3 years to improve the soil naturally. I think it works for a small garden plot such as this, and the huglekulter mounds, to invigorate life into the soil right away, essentially jumpstarting the mycology. It may not be superior to no till/no dig in the short term if Perennial production is the goal, but if you need food security now, and food storage for winter, this is a solid gerdening method.

I learned a lot from this post, especially the part about clay enhancing the growth of roots due to negative ions. How cool.

Thank you both for your input and thanks for this detailed post ZM!

 

[eco2pia]

I have sand and glacial till. Possibly the worst soil I have ever seen.

I previously dug clay soils one time to incorporate initial organic matter, and loosen the soil, and I have dug up a compacted gravel driveway to bring it back to arable soil, but here it just seems to be a losing battle. I have chosen no till and copious applications of municipal and home made compost and manure. The sand, rock, and fine mineral dust that comprises my native soil is incredibly poor and hydrophobic to the point that I can't get water into the soil without a huge blanket of mulch. Nutrients wash away immediately, and water applied to the surface either beads up and runs off or drains straight down to the center of the earth immediately.

 

[Zee-Man]

You are promoting a lot of hard work that actually do more damage that good for what you want to achieve.

You may have some great information, specially when it comes to scales of mass prairie or pasture land. However, the empirical evidence over 30 years or so in various piedmont soils shows greater yields and drought survival.

You may see in the third picture above how verdant the double dug garden is compared to the surrounding yellowed and dying grass in the undisturbed ground. You can even see the nutrient starvation in the single dig.
As to no till, many plants won't even germinate if exposed to too much UV-B light. Many weeds enjoy no till since they tend to germinate with lots of UV-B. Not all perrenials take huge amounts of time to spread a root system. Mulberry and Maple both establish deep taps before they have much canopy.

In another local sub-system the soil is composed of large ore and basalt under very thin O and A horizons. Composed chiefly of Red Oak, Beech, and Poplar. It has the appearance of old growth even though it is only about 250 years old due to the weak roots systems leading to wind felling. Since there is essentially no B horizon and the C and R horizon is so close to the surface even though there is extensive canopy, erosion is a constant problem.

 

[Sapphire16]

What an excellent and informative talk! Thank you!

 

[eco2pia]

I think if I could get ENOUGH organic matter maybe double digging or trench composting (which is more like slow double digging, with all organic matter going to the bottom of the trench about 20 inches down) might work. I may try some variation of this on the raised bed vegetable garden I am planning for next year if I can get a truck load of arborist mulch in the fall. Time, material and manpower are definitely all limiting factors.

No till methods will get me there eventually and I will be able to plant SOMETHING in those areas (in the mulch layer) immediately, but I am stuck amending and watering for years more.

In areas with reasonably healthy soil, structure will rebuild in a double dug bed and in the end (within a year) you will have really great soil. With years of topdressing organic matter the worms will eventually dig it under and you will have really great soil. One is faster, the other takes less work but it is slower. The result is similar.

I did start by trying a double digging method without massive amendments of organic matter when I bought this place a few years ago. On my sandy poor soil, the soil gained volume, but not fertility or water holding capability, and I discovered that the A and O horizons are less than an inch here. There is almost no structure to preserve, and all that can be gained by digging is removal of large stones and some reduction of compaction, which is not necessarily a good thing, as it promotes erosion. I had to modify my method to suit the conditions. It has been a learning process.

I envy @Zee-Man his healthier soil, and one day my place will be a fertile oasis in my neighborhood. It actually already LOOKS that way--thru carefully choosing plants that are adapted to our local conditions, rather than trying to force thirsty things to grow here. My neighbors are amazed, lol.

 

[Heartbased Homestead]

That's pretty informative Zee-Man and eco2pia! I didn't expect to pick up advanced soil and botany knowledge here. Y'all are a treasure for a new gardener like me.

 

[kusanar314]

I think if I could get ENOUGH organic matter maybe double digging or trench composting (which is more like slow double digging, with all organic matter going to the bottom of the trench about 20 inches down) might work. I may try some variation of this on the raised bed vegetable garden I am planning for next year if I can get a truck load of arborist mulch in the fall. Time, material and manpower are definitely all limiting factors.

No till methods will get me there eventually and I will be able to plant SOMETHING in those areas (in the mulch layer) immediately, but I am stuck amending and watering for years more.

In areas with reasonably healthy soil, structure will rebuild in a double dug bed and in the end (within a year) you will have really great soil. With years of topdressing organic matter the worms will eventually dig it under and you will have really great soil. One is faster, the other takes less work but it is slower. The result is similar.

I did start by trying a double digging method without massive amendments of organic matter when I bought this place a few years ago. On my sandy poor soil, the soil gained volume, but not fertility or water holding capability, and I discovered that the A and O horizons are less than an inch here. There is almost no structure to preserve, and all that can be gained by digging is removal of large stones and some reduction of compaction, which is not necessarily a good thing, as it promotes erosion. I had to modify my method to suit the conditions. It has been a learning process.

I envy @Zee-Man his healthier soil, and one day my place will be a fertile oasis in my neighborhood. It actually already LOOKS that way--thru carefully choosing plants that are adapted to our local conditions, rather than trying to force thirsty things to grow here. My neighbors are amazed, lol.

Your situation reminds me of a guy I was following online that moved to the Philippines and was dealing with kind of the opposite problem you are. You have hydrophobic soil, he had sand that would just take all of the water and dump it in the ocean... He had chickens and bedded them on rice hulls (easy enough to obtain out there) and used that bedding to fix a few square feet of land at a time until he had enough decent soil to actually be able to grow something other than coconuts.

 

[eco2pia]

This has been my strategy so far, one bed at a time. And yes, once you get past the beading up and rolling off, the water drains straight down, presumably to the center of the earth. an inch away from a soaker hose that ran for an hour the soil is bone dry.

 

[dlynn]

I think if I could get ENOUGH organic matter maybe double digging or trench composting (which is more like slow double digging, with all organic matter going to the bottom of the trench about 20 inches down) might work. I may try some variation of this on the raised bed vegetable garden I am planning for next year if I can get a truck load of arborist mulch in the fall. Time, material and manpower are definitely all limiting factors.

No till methods will get me there eventually and I will be able to plant SOMETHING in those areas (in the mulch layer) immediately, but I am stuck amending and watering for years more.

In areas with reasonably healthy soil, structure will rebuild in a double dug bed and in the end (within a year) you will have really great soil. With years of topdressing organic matter the worms will eventually dig it under and you will have really great soil. One is faster, the other takes less work but it is slower. The result is similar.

I did start by trying a double digging method without massive amendments of organic matter when I bought this place a few years ago. On my sandy poor soil, the soil gained volume, but not fertility or water holding capability, and I discovered that the A and O horizons are less than an inch here. There is almost no structure to preserve, and all that can be gained by digging is removal of large stones and some reduction of compaction, which is not necessarily a good thing, as it promotes erosion. I had to modify my method to suit the conditions. It has been a learning process.

I envy @Zee-Man his healthier soil, and one day my place will be a fertile oasis in my neighborhood. It actually already LOOKS that way--thru carefully choosing plants that are adapted to our local conditions, rather than trying to force thirsty things to grow here. My neighbors are amazed, lol.

I have gardened in clay and now in sand. Sand won't hold water and leaches nutrients quickly. The solution for both is adding organic matter. Digging a trench and adding old logs(I've found big wood breaks down faster than sticks) will create a moisture resivore.flat instead of raised like a hugel worked better for me. mulching is great but added to the destruction by voles and ground squirrels. The magic this year was Bunnie berries. I stir in, top dress, sometimes open pockets with a trowel and fill will the rabbit and quail poo. In 50 years of gardens never had such a pretty one. And rabbit manure is safe to keep adding fresh all year I've read , think of them as pellets of peat and slow release fertilizer
.so it's a constant improving not all at once.. someone said you can compost in a year in a pile or one day thru a rabbit. I give them a pail of weeds, veggie trimmings, and tree trimmings
They give me a pail of garden gold!

 

[eco2pia]

I also just discovered straw bale gardening, which I plan to use in a few awkward places next year!! In the "make organic matter fast" category, this should be extra neat. I plan to take the lazy route there too, and lay out my bales along a fence this fall, topdress them with chicken manure and let the rain get to them all winter, so that in spring they are ready to plant peas in before the last frost. This process can be sped up to about 14 days by watering chemical fertilizer in, but my method will use resources I already have. At the end of the growing season I will have really nice mulch to use elsewhere. Exciting!

 

[Zee-Man]

I think if I could get ENOUGH organic matter maybe double digging or trench composting (which is more like slow double digging, with all organic matter going to the bottom of the trench about 20 inches down) might work. I may try some variation of this on the raised bed vegetable garden I am planning for next year if I can get a truck load of arborist mulch in the fall. Time, material and manpower are definitely all limiting factors.

For your situation a hybrid of raised bed and hugelculture may be quite effective. It will take some time though. I would dig down say 12 inches. Raise the sides of the bed. and lay in some wood. Firewood might be a good choice. Ground tree scrap for an arborist is a good choice too. Sounds like you might have that source lined up. Take the soil that you dug up and mix it with leaf mold and compost.

Here is where the time comes in. You will need even more soil. Either you scalp soil from other locations, garner some from construction sites, or buy it. You will want to enrich the former two the same as you enriched the soil you dug out. Growing all that compost takes time.

In the future you will need to repeat this as soil filters into the wood layer and as the wood rots. Build your bed with a removable end so you can get a tiller in there to add more leaf mold over time.

 

[kusanar314]

I also just discovered straw bale gardening, which I plan to use in a few awkward places next year!! In the "make organic matter fast" category, this should be extra neat. I plan to take the lazy route there too, and lay out my bales along a fence this fall, topdress them with chicken manure and let the rain get to them all winter, so that in spring they are ready to plant peas in before the last frost. This process can be sped up to about 14 days by watering chemical fertilizer in, but my method will use resources I already have. At the end of the growing season I will have really nice mulch to use elsewhere. Exciting!

I'm not sure if they are in your area, but check and see if Chip Drop would be available for you. It's basically a brokering website where homeowners say " I want mulch" and tree companies can look on there for places to dump loads of mulch. It costs the tree company (last I looked) $20 to get the address to dump at, it costs the homeowner nothing unless they voluntarily pay the fee to "sweeten the pot" for the tree company in order to increase likelihood that they will get deliveries. But $20 for a truckload (which is typically a dump truck) of mulch (fresh chipped) isn't bad at all and would help you get that organic mass you need.