Improving Heavy Clay Soil and Maximizing Potato Production, by Tunnel Rabbit

This video: How to Make Inexpensive Garden Container Mix: Organic Fertilizer, Lime, Peat Moss, Compost & Dirt shows us the proportions of the basic materials discussed that can be used to make an ideal soil, but it is only a starting point when working with clay.  Last year I was able to incorporate heavy clay as an unmeasured part, using similar methods demonstrated in the video.  The proportion used is unknown as it was my first attempt, and the goal was to produce as much usable soil with the least amount of manure. Ordinary topsoil was used in the video, but we must contend with clay, that is a different animal. A little bit of clay can go a long way to messy up the quality of soil needed to grow a garden, yet it can provide valuable nutrients as well, and is needed as a binder.  It is not all bad, my worms love it, but my potatoes do not.  In other words, additional amendments are needed relative to average topsoil to adequately dilute clay, or add enough organic matter.

In my opinion, a higher percentage of peat moss or manure will be needed when mixed with heavy clay. Yet is the price of peat moss worth it? A local commercial source quoted me $70 per cubic yard.  My neighbor has a small pile for $25 per yard.  Peat moss is excellent, but spendy.  To make soil that is good enough, and not ”awesome” soil, as I did last year using clay, required lots of composted cow manure as the primary material to dilute, or reduce the presents of clay and it’s undesirable characteristics. Any manure should be thoroughly composted before being used.  I simply mixed it into the clay until it was lighter and looser paying no attention to proportions.  It was not awesome, but good enough, and it produced lots of potatoes and a bumper crop of tomatoes. We do not have to attain the high standard, or ”awesome” soil level for our soil mixture to be ‘good enough to grow a meaningful amount of veggies. However, potatoes and other root veggies need as light and fluffy soil as possible to maximize their growth.

Therefore it might be worth the effort and expense of creating soil specifically for potato production, and use more compact soil for other veggies.  As a staple crop, potatoes are very important, and peat moss is the antithesis of clay, and best for the job.

That said, this year, I am attempting produce ”awesome” soil as an experiment, and will attempt to grow as many potatoes as possible using only one raised bed that is 12 inches deep and 90 square feet. The results of the experiment will determine whether, or not there is a significant improvement when using ‘awesome’ soil, versus good enough manure/clay mix.  For ‘awesome’ soil, one part of homemade compost was added to one part of last year’s soil to produce ”awesome” soil texture, and maximum nutrition in an attempt produce a maximum yield from my home-grown seed potato. It is an attempt to grow as many spuds as possible, using the least amount of space possible.

In Montana, tall and strong fences that are needed to keep the deer and elk out. Could it be that it is less expensive and less trouble to maximize yields, than to expand the garden? Any way we slice it, and the answer is yes. As we are also producing not only calories, but nutrition, or quality versus quantity.  IHMO, to get the most from one pound of seed potato requires the highest quality soil possible that is 12 or more inches deep.

Here is an article that may change the way we grow potatoes. It explains why traditional practices were practiced, yet the reason has been mostly forgotten in the YouTube world: Seven Critical Tips to Improve Potato Production in Beds and Containers.

Should composted cow manure be available, and because it can be much less expensive than peat moss, often free, that is what I would normally use. In the next experiment, because the peat moss to free to me, I will start with 25% peat moss and 25% cow manure with 50% clay soil, and when there is no more peat moss, it will be 50/50 manure to clay, or as much manure as you please.  The Manure is free to me too. It is proven to work good in the past. IMHO, these percentages will not produce ‘awesome’ soil, but very good soil. I’ve run out of compost for this year.  The addition of 25% or less compost blended, or at the bottom layer for potatoes, would be ‘awesome’. Having nutrition throughout the soil depth is important for tuber growth (see the article).  One can see the root structure, and the stems the potato uses to grow the tubers, and to feed that tuber at that depth, if one pulls the intact plant out of the soil for examination.  The lack of substantive, or good soil over the potato seed, produces fewer potatoes, but a depth greater than 8 inches above the seed potato, is at the point of diminishing returns in terms of potato production.  The Ruth Stout method therefore as the smallest yields, and risks damage by pests.

A Warning on Using Sawdust

I believe that peat moss will do a better job than cow manure to break up the structure of clay, as it is a stable form of organic matter that decomposes slowly over several years, and both retains and drains water better than manures. This is why it is used as the predominant ingredient in potting soils, and used to start seeds.  It is has the highest concentration and is stable organic matter, however, nutrition will also have to be mixed in, as it is mostly bereft of nutrients.  Because there is limited amount of peat moss I can use for free, and because I have hundreds of pounds of chicken manure mixed with straw, that is what I will use for all non-root crops.  As another experiment, some of the chicken manure is mixed with fine sawdust that was composted for about a year.  Sawdust has an extreme high carbon content, yet mixed with high concentrations of nitrogen from chicken manure, it does appear to compost quickly, however, after a year of composting it still processes the strong smell of ammonia. Even after one year, it still may not be thoroughly composted, yet it useful as a top dressing and can be spread evenly like a granulated commercial fertilizer. The texture of sawdust would be excellent for making clay lighter, and any soil  ”awesome”.  As a top dressing, the topsoil produced over the clay can be next year used for a no-till garden.

Worms love the clay around.  There are obviously lots of good things in it for them to eat.  Using sawdust with chicken manure could be another strategy, however, I do not recommend using sawdust in the garden in general, or in mixed compost piles, as it has an exceptionally high carbon content value of 500.  Please avoid sawdust if at all possible, unless it is thoroughly (multi-year) composted in a segregated compost pile using a layer of soil between thin layers of sawdust.  If not properly composted, it will sequester the available nitrogen to feed bacteria, and deplete the soil, and starve the plant, or retard the composting material of vital nitrogen it needs to compost in the usual time frame.  It can take longer than 1 year to become adequately composted. I will only use my experimental chicken manure/sawdust compost as a side, or top dressing because of that risk, and until I have enough experience with it.

Straw has a much lower carbon value of 150, versus sawdust and works well in the chicken coup.  Chickens love both straw and sawdust. And I have a limitless supply of sawdust.  However, straw mixed with chicken manure and composted, is a much safer way to go, a better bet, if attempting to amend soils. We should seek a 1 to 1, or higher nitrogen to carbon ratio in our compost.  The more nitrogen, or fine green matter in the compost pile, the better.  The best all-around fertilizer for most veggies, is cow manure, and compost, and that is used primarily with my root crops, but the chicken manure is amazing stuff for everything else.  Too much nitrogen causes root crops to have wonderfully tall and lush tops, but stunts the growth of the root we would eat.  Heavy clay can be nutrient-dense as well.

The stuff around here grows potatoes tops well, but the compact soil diminishes the growth of tubers.  Because of clay’s dense structure, the potato can not bust it up enough to grow to full size, or at all.  The problem with clay is it’s severe lack of organic matter.  Fortunately, manure and peat moss are not the only organic matter we can use.  Composted leaves and weeds are excellent too. Tip, get the weeds before they go to seed. There are many ways to add organic matter of any kind to clay, even composted pine needles can work.  Clay can be slightly alkaline and addition of acidic soils, or compost can provide a neutral balance. Pine needles lose their acidic pH once composted. Look for what is available and use it! But for potatoes, I want a pH closer to 6, so do get a test kit.  Having the correct pH is vital for the correct soil biology and chemistry that unlocks, or makes available the type and quantity, of nutrients needed for a particular plant. I would have dedicated soil for certain plant types that will grow much better with a given soil pH.

The primary reason for attempting to grow a maximum amount of potatoes this year, is to produce an excess of seed potato for the following year. After adding 30 percent compost, and a roughly 50/50 mix of manure with clay, there is acutally very little clay in my best attempt at using the very best growing medium possible that promotes the greatest potato production.  If I could, I would also like to source a naturally occurring source of additional K or potassium.  Wood ash is good, but that also lowers pH.

The Potato As A Survival Food

As the potato is an excellent choice for a survival food, we need extra seed potatoes to give to friends and neighbors, so that they can grow their own. Prior to the Great Potatoe Famine, the Irish could more than subsist on a diet that contained mostly or all potatoes. With an excess of potato seed,  we could also grow a monster crop that can be used to feed a family that is not up to speed or use it as barter. I expect that the supply of seed potatoes at the retail level could be next spring, be inadequate, or even nonresistant. Last year, because of Covid, I supplied friends with seed, because seeds at the store where sold out. Seed potatoes are not stored in sufficient quantity, or at all, by most gardeners, but they should be.

Disclaimer: I am only a novice gardener, and everything I do is an experiment.  Living in a remote region and off grid often requires one to innovate, and learn by trail and error.  Resources are scarce out here.   Regardless of the actual results of any experimentation, a useful result will be had, and it would never be an unproductive move to improve the soil. It will be there for future experiments, as each year is actually another, in an endless series of experiments, when growing stuff involved.  Improving the soil should be a constant endeavor.