Before I get into today's post I'd like to thank all of you whom turned out for the Neighborhood Grange meeting at the Cape Fear Museum. All of you were a great audience and I hope the talk on soil preparation was useful. For those who could not come or, those too far to come to the meeting, here is a shortened recap of what was said at the meeting by me, and as always don't be shy about emailing or posting me questions or comments. Thank you for reading.
Often we don’t take soil very seriously, some assume it will always be there, and then once it is eroded away we wonder what went wrong and may even balk at the cost of undoing the damage that we have wrought by inaction. Civilizations have seen decline due to poor stewardship of the land and the real mark of a people’s success can be seen in the imprint they leave upon the lands on which they live. Thus we have today’s topic your soil, and how you can best prepare it for the year ahead.
Some of you maybe heard the old horticultural adage that ‘Dirt is merely soil that is out of place.’ And such a maxim is quite true, the dust bowl’s infamous dust storms were essentially large particles of eroded sub soil borne on the wind due to erosion of the top soil and the demise of the vegetation that once held the soil in place. But how does soil get displaced exactly? First you need to know a little soil science to understand where soil comes from and how you can damage it thus causing erosion.
Out side of those in the agricultural or, environmental sciences it is a little known fact that the soil is composed of layers. These layers are called horizons and each one is for lack of a better description is a state of transition. Soil itself is composed of several things, minerals, organic matter and deposits of chemicals. Each of the three plays a critical role in the process of the varied horizons that form over millions of years. The birth of soil itself starts with the weathering of rock into smaller particles, these particles continue to break down through organic, chemical and environmental processes until by particle size they become sand, clay and silt type materials. The presence of metals and deposits of other minerals will add both color and nutrient value which then is fed upon by microorganisms and plants which further the action of these particles being broken down.
The soil itself is scientifically broken down into anywhere from three to five primary horizons depending on which book or expert you consult. It is generally agreed upon however that the horizons from top most to the bed rock are O, A, B and, C horizons. Each horizon is essentially a state of transition, from the parent material (bedrock) towards the final material (topsoil.) In order from the top soil downward towards the bed rock the horizons are best defined as follows.
1. The O horizon is usually the first 2” inches of the soil and is composed of mainly organic matter that is in varied states of decay.
2. The A horizon may be upwards of 6” deep on average, this is the horizon where the fully decayed organic matter accumulates and bears a large amount of soil life forms.
3. The B horizon is often around 30” deep and is commonly called the subsoil. This is where the clay, iron, aluminum and organic residues tend to finally accumulate.
4. The C horizon is the horizon in which the parent material breaks down to form materials for A and B horizon.
5. Depending on who you ask, some sources will consider the bedrock itself an additional soil horizon.
For our purposes we need not worry to much about the bedrock, B horizon or C horizon because chances are we will likely not dig deeper then perhaps a foot and normally this foot is covered by O and A horizons for the most part. With all of that said, it takes a long time for bedrock to weather to make just C horizon, and in the same way it takes just as long for topsoil and the supporting vegetation to develop. Topsoil is a resource that is perpetually undervalued and critical to our survival, no topsoil no food.
Now that you know where soil comes from, and why it’s important, here is what you can do. In at least the state of North Carolina you can send off soil samples to the agricultural extension agency for free. I recommend doing soil tests at least once a year regardless of the state you live in. These soil tests will tell you what sort of soil you have and provide recommendations on what you should do to improve it for your own purposes. One thing to remember is to collect the samples with tools and containers that are not made of galvanized steel or anything zinc plated, as both can skew your test results. If you send in soil samples now, and perhaps again in late fall the turnaround time for getting a report back will be fairly quick. Once you have your soil test results in hand or on screen as they tend to send you info by email, you can proceed to the nest step.
Preparing the soil is as much knowing what soil you have and testing it as it is knowing what you are to grow. If you are into growing members of the cabbage, melon or mallow family you can expect you will need to fortify the soil with nutrient and organics to keep up with their heavy feeding habits. In comparison tuberous crops such as yams, potatoes, turnips, rutabagas, peanuts, carrots, parsnips and, radishes will need a deeper then average soil with a loose texture and balanced nutrients. In the same way vegetables in which you eat the fruiting bodies such as cucumbers, tomatoes, eggplant and peppers can make do with soil of at least 6” depth but need nutrients to do best.
The first thing to consider is your soil amendments. Obviously there is no shortage of options in this department and at any given garden center you will likely be bombarded with sometimes understandably excessive claims.
1. Peat moss: a good source of organic matter, it acidifies the soil a little, may require wetting before use and comes from non-sustainable sources.
2. Coir Fiber: An excellent contrast to peat moss, it is pH neutral, comes from coconut husks and is sustainable, a bit pricy, but this will change as it sees more distribution.
3. High Potency Manure: Products such as Black hen qualify as their nutrient level is often two or three times higher then normal composted manure. The price is often double, but a little does go a long way.
4. Composted Manure: Generally sold as composted cow manure, this soil amendment does not burn, produces instant soil improvement and is reasonably priced. The downside is you don’t know what the cows ate and the quality can greatly vary.
5. Agricultural Bi-product: The best example of this is Mushroom compost which is the fully decomposed logs left from mushroom growing. Generally nearly neutral pH, reasonably reliable in quality and scent-free, this stuff is good but may be pricy.
6. Worm Castings: These are the fecal matter produced by worms in a vermiculture setting and are probably the least-gross of the manures. They don’t need composting, they don’t smell and they don’t burn plants, in fact you can even use one cup per gallon of water to make one hell of a compost tea. The problem is that they can be expensive for use in large areas.
7. Home Compost: this is your compost, the advantages and disadvantages are the same, you know what’s in it, and its quality varies based on the time you spend working on it. Home composting is the closest one can get to making natural topsoil.
8. Mulch: All mulch serves a primary purpose, that is to prevent wind and water based erosion, while also looking nice. It also serves the secondary purpose of simulating natural leaf-litter and breaking down to add to the topsoil. As a result mulch effectively is the cheapest soil amendment imaginable. Certain mulches do have effects on the soil, pine straw and park acidify, rubber much leaches zinc into the soil, and cedar and cypress mulches may repel termites.
9. Potting soil: Potting soil is probably the last resort soil amendment, its nutrient value is questionable, and some mixes come with added chemicals that may not help you very much. However if you are dealing with pure clay or pure sand, flooding the bed area with 3:1 ratios of cheap potting soil (ie Hyponex) may be the fastest way to kick start a garden and set a decent if nutrient poor foundation to improve from later.
10. Coarse Amendments: Sometimes the soil is so hard to deal with one must resort to macro-particle amendments such as perlite, vermiculate, construction sand, or even ultra-fine crushed gravel to gain any traction. Coarse amendments do nothing for nutrient and only exist to help bust through severe hardpan or Caliche type soil conditions, Green sand pay help break down the clay, but ultimately this is a drainage solution.
Needless to say, your soil test should determine what amendments to use as it will tell you your soil structure and what you should do. There are three final thoughts to soil preparation to consider before you start applying materials anywhere. Firstly is the placement of your beds where you put a garden bed determines what will grow, how much amending and how much fertilizer you will need. For instance areas that flood during rain storms may need to be raised and walled to prevent the mulch and soil from floating off as well as the nutrients from leaching away. Areas near roadsides may need extra mulch to keep the soil cool in summer and limit soil freezing in winter, and also may need additional water. Beds near structures and stone or concrete paths will likely be in a micro-climate and thus soil amendments should be tailored specifically. Also the orientation of a bed in consideration of the sun’s path through the sky may determine what you can or cannot plant.
Second, one must also consider the prior years of growth, specifically what was there before, and what you intend to put there now. Repeated planting of the same crops in the same spots will slowly in most cases deplete the soil of specific nutrients. So consider soil replenishment on an annual basis. An alternative is to consider planting heavy feeders with plants that naturally replenish the soil, such as legumes and cabbages.
Third know the nutrient needs of your plant stock, some plants become a weed if over fed while others don’t produce what you want if they aren’t getting the right nutrients. For instance, Nasturtiums will produce tons of leaves but no flowers if they get too much nitrogen. This is great if you like the leaves as salad greens but terrible if you want the buds for pickling or the flowers for attracting pollinators.
The last factor to consider is your soil’s basic pH and what your plants require. The soil’s ph effects what nutrients are available and in what amounts with this in mind it’s a good idea to try keep the soil ph between 6.0 (low acidic) and 8.0 (low alkaline) or roughly neutral. Most plants will do well in that range and most soil borne nutrients are available to plants in that range as well.
In conclusion I hope this somewhat long article about soil preparation was useful and as always you can send in questions to the email attached to this blog. Next weeks article is ‘The life and times of a Black thumb’ and is about house plants that even a black thumb can grow; thank you for reading.
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