Know thy soil (*adaptation of a famous maxim by some ancient Greek guy).
This is very important, whether you are actively trying to grow anything on your land or you are simply conscious of taking care of the environment. If the former, your dirt will affect what is produced from your land; if the latter, your dirt can contribute to or contaminate runoff in your watershed. Either way, it is good to know what is going on in your surrounding soil.
The biggest takeaways from this post are:
-Work with the soil you have (don’t try to change its texture, you end up messing with many other factors like flora and fauna), and
-Everything in moderation (adding amendments).
Before you add anything at all to your soil, test it. Carefully collect a sample and send it off to a lab to get an accurate reading on what is going on with your dirt. Most universities with good Ag departments will charge you around $15 for a more in-depth analysis than you will need, and include recommendations for what to do next to improve your soil.
Follow the instructions on the university’s Ag department webpage to collect your soil and send it off, but in case you can’t find any instructions, here is a good list, which can be found on UMass Amherst’s page:
-Note what purpose you will use the soil (vegetable garden, grass, shrubs, etc.)
-Record the measurements of the area you are testing
-Using an auger or a trowel, dig out soil from three to five separate spots within the plot and mix them together thoroughly in a pail of a nonreactive substance (plastic or stainless steel)
-Scoop out approximately a cup of dirt from the mixture and let it dry out thoroughly on newspaper (return the rest of the dirt to your garden)
-Once the soil is completely dry, drop it into a zip-lock baggy, label it, and send if off
Before starting my summer vegetable garden bed, I had a sample of my soil tested at UMass Amherst, and I found out that my “Phosphorus is excessive!!!” (They actually typed three exclamation points, no exaggeration.) If you are of the environmentally conscious camp, this is important information because too much Phosphorus (the second number in fertilizers, which promotes blooms) in runoff from a heavy rain can promote algae blooms in your watershed – very bad for water-dwelling creatures.
Do not stop at testing only your vegetable garden soil, go ahead and test your lawn soil and other beds to determine what you can do to improve it, but keep the soil samples separate. And in the mean time, do NOT over-fertilize your soil. You may remember hearing about the algae blooms in Lake Erie by Toledo. These were largely caused by runoff from people trying to achieve that uniform greenness by over-fertilizing their lawns.
Single-grass lawns are actually quite unnatural and particularly susceptible to runoff. You are better off having a naturalized, wild grass (not weeds, not as lazy as that) front yard, which collects and absorbs more water than it lets run off. You can still achieve an organized, polished horticultural look, it just won’t be an overall smooth, emerald green lawn. If you do keep a grass lawn, mixing your grass seed is the best way to ensure an overall healthy lawn – ie: hardy fescue with ryegrass and bluegrass.
Enough of grass, this post is supposed to be about dirt.
The reason Phosphorus is so darn excessive in my garden soil is because I had blissfully and ignorantly added compost and manure and other natural amendments to my garden bed last year. While this is in no way harmful to the veggies I intended to grow in the bed (I called the lab at UMass to make sure), I do need to be mindful of corralling runoff, and keeping my soil contained in that bed. After a few years, the Phosphorus levels will return to safer runoff levels.
Aside from having the nutrient and mineral content of your soil spelled out, there are lots of physical characteristics to understand about your bit of earth. To learn more about your dirt, you will need a good, sharp shovel. Skip the cheap shovels and invest in a 9” round-mouth shovel with a thick, sharp blade. If you notice it getting dull, you can sharpen it with a file – a sharp blade makes dirt-work much easier.
Start by marking off the area where you intend to get “dirty”, and dig down in several spots until you see changes in soil color, density, texture, etc. Make a note of these characteristics, as they are very important for figuring out what you intend to do in this area. Is your soil very cloddy and clay-rich? Is it loose, low-lying, and muddy? Clay soil is fine for growing a wide variety of plants, while a limited type of plants thrive in low-lying, muddy areas. It doesn’t hurt to make note of what any roots are doing in the area in which you are digging – shallow, horizontal roots, or ones that drastically change direction, can indicate compacted soil. If you have compaction, you will need to break it up by breaking it up with a shovel (be prepared for some hard work) and mixing in organic matter like compost. Another way to help prevent the compacted soil from re-compacting is by immediately planting something with deep and vigorous roots like alfalfa.
Texture vs. Structure
Soil texture, not to be confused with soil structure, comes in the form of sand, loam, silt, clay, or some combination of those four. Texture is the mixture of these particles’ sizes, and how the dirt feels in between your fingers. Structure is how the particles fit together. Sandier soils are structureless and drain very quickly, but run the risk of losing organic matter. As you progress from sandy soils through loam and silt, and on to solidly-structured clayey soils, clay hangs on to water and nutrients, but is slow to drain.
The ultimate lesson about soil texture is that it is impractical and sometimes impossible to change it. If you have a very clayey soil, practically speaking, you cannot add enough sand to it to change the texture. It is best to work with the soil texture you have and grow plants that naturally thrive in it. If you attempt to change it, you can cause harm by diluting the nutrients and organic matter, and disrupt the natural flora and fauna. That is not to say that you cannot physically replace all of your soil with something more suitable to your purposes, but that would require heavy machinery. Or you could always build raised beds.
Your Soil Has Chemistry
A quick note about the pH of your soil: Soil naturally becomes mildly more acidic over time because of natural and human input and output (acid rain being a contributor).
Do not guess what your soil’s pH is, it can be incredibly variable in a small space – best to measure it. High clay or organic matter content of a soil buffers it from susceptibility to pH change (ie: it is neutral and remains neutral without drastic input). Coarsely textured soil with low organic content is much more susceptible to pH change.
Most plants will tolerate a wide range of soil pH, but low pH can occasionally stunt growth. Blueberries, azaleas, and rhododendrons are a few plants that love acidic soil and will not thrive and fruit/flower properly without enough acid. As long as the pH of your soil does not dip below 5.5, most other plants will generally be fine. If your pH does dip below the optimum range of the plants you wish to grow, you can add garden lime to your soil, which will bring your pH balance closer to neutral. Note: Gypsum is not an alternative to lime. Second Note: It is very difficult to lower a high pH.
You can decrease the pH of your soil (make it more acidic) by adding natural ingredients like pine needles, but very large quantities are necessary to change it, and with variable results. The benefit of natural ingredients to lower pH is that they have an immediate impact as well as a long term one as the materials break down.
Work Your Dirt
Tilth is the state of your soil as it relates to growing plants. Good tilth means an arable, stable soil structure. If you have big clods of dirt, cycles of freezing and thawing and of wet and dry will break these clods of dirt up better than manually doing this yourself. Tilling your soil gently can add valuable air to it, as well as mix in nutrients for plants to more easily absorb.
Once you have had your soil tested and you get the results back from the lab, you can begin to work on the overall condition of its structure, fertility, acidity, and drainage. Soil should ideally be about 50% pore space (approximately equal portions of water and air), 45% minerals, and 5% organic matter. Your lab report should include the content of nutrients and structure, as well as recommendations on how to improve your soil for the purpose you listed. In the case of my excessive Phosphorus above, I had added way too much organic matter to my soil, and my only recommendation was to add some Nitrogen; the structure was fine (not too loose and sandy, and not too thick and clayey, but somewhere in between).
Now that you know your nutrient and mineral content and the texture and structure of your soil, you can get to work modifying nutrients and structure to realize the full potential of your spot of land!
“I find that a real gardener is not a man who cultivates flowers; he is a man who cultivates the soil.” –Karel Čapek, The Gardener’s Year
Reid, Keith, Improving Your Soil: A Practical Guide to Soil Management for the Serious Home Gardener, Firefly Books, 2014.