The DIRT on DIRT

We walk on it. Children play in it. We hate it on our cars and collars. Sometimes we even make dirty jokes. But when it comes to growing flowers and vegetables, dirt is no joking matter!

To a plant, dirt is much more than a place to put down roots so you don’t blow away in a storm.

Ideally, dirt provides a reservoir of water to get plants through dry spells; however, some kinds of dirt can hold too much water and drown plants while others simply do not have the ability to hold water for any length of time.

Dirt also is a source of vital nutrients for growing healthy plants. In fact, if your soil is truly healthy, your plants should be able to get ALL of their nutrients from the soil, without any amendments. That’s a difficult goal to achieve, but, with patience and perseverance…

Dirt is also, hopefully, a source of beneficial microorganisms that help your plants assimilate the nutrients that are present in the dirt.

While it’s very true that you don’t need perfect dirt (okay, soil) to grow a beautiful or productive garden, having soil that is fertile, full of organic matter, loose, well drained (but not too well drained) can make a significant difference.

I’ve spoken briefly in previous columns about the need for testing your soil to be able to accurately figure out what amendments it does/does not need.

I suspected my soil here was on the alkaline side. Most vegetables need a pH of between 6.0 – 6.5, slightly acidic, to have the best chance for growing and being healthy. Most will grow outside of that range, but that is the range of highest productivity for most vegetables.

If the pH of your soil is either too high (alkaline) or too low (acidic), your plants won’t be able to get the nutrients they need even if you apply fertilizer, although fertilizer may help to bring the pH closer to what it needs to be, depending upon what you use.

If the pH is below 6.0, nitrogen, phosphorus, and potassium absorption will be inhibited.

If the pH is above 7.5, iron, manganese, and phosphorus will be less available to your plants.

My soil tested out at 7.1, OUCH! That’s too alkaline for happy vegetables, in general, but that doesn’t mean my goose is cooked. It does mean I have to make some choices.

  1. I can put up a lot of raised beds to grow my fruits and vegetables in a commercial dirt mix (this is the most expensive proposition, but may be doable depending on how much you want to grow and how much you can invest), and/or,
  2. I can put in a lot of soil amendments to make my dirt more acidic, a process that takes time when done organically – as I prefer, and/or,
  3. I can focus on fruits and vegetables that actually prefer alkaline soil, and/or,
  4. I can focus for the short term on alkaline tolerant plants while working on gradually making my soil more acidic.

It truly is very important to get your soil checked at least every couple of years. That way, you not only know what you’re starting out with, but you will also be able to track your progress over time. This checking can be done with a kit from the local garden center or online sources, or, it can be done by a lab.

In addition to pH, you also need to know how much organic matter there is in the soil already and approximately what percent of the soil is clay/silt/sand. Knowing how much nitrogen, phosphorus, and potassium are present and in a form that is able to be absorbed by plants is also important for top production.

A quick and dirty way to figure the amount of clay, silt, and sand in your soil is a mason jar test. Put 4” of your soil (no rocks) in a mason jar, add 1 Tblsp of dish detergent. This soil should come from the root zone of your garden and, if your garden is large, pull some dirt from several areas. Fill the jar with water, shake well, and then leave it sitting undisturbed for a couple of days. The results should look something like this:

Mason jar test

Now use a ruler to measure each of the three layers. The bottom layer is usually sand since it’s heavier than silt or clay. The middle layer will be the silt layer which is usually darker than sand. The top layer, clay, is usually lighter in color than the silt.

The total depth of all three layers is your 100% level so, if you have 3” of total “stuff” in the bottom of the jar and 1” of each of the layers, your soil would be 33% sand, 33% silt, and 33% clay.

Now compare your results to the USDA soil triangle.

Soil triangle - USDA

Using the results in the example above would suggest that you had clay loam as your soil type.

Loam is what you want to have, but, all of the soil types can be worked with.

Loam is dark in color, soft, dry, and crumbly in your hands. It has high organic matter and releases nutrients to your plants gradually and in a way that generally supports good plant health. It’s fertile, drains well, is very easy to work with, and most plants love it! It’s the perfect balance of the three soil types.

We’ve all heard about old time “snake oil” remedies that were purported to cure pretty much everything while in reality, they were somewhere between outright poison and simply not helpful.

Please don’t think of me as a “snake oil pusher,” but whatever your soil type, there truly is one magic bullet that will improve it and move it closer to that beautiful loam that you want, or help keep it that way if loam is what you have: COMPOST.

Put simply, compost is partially decomposed carbonaceous materials, i.e. plant matter.

“If a healthy soil is full of death, it is also full of life: worms, fungi, microorganisms of all kinds … Given only the health of the soil, nothing that dies is dead for very long.”
~Wendell Berry, The Unsettling of America, 1977

If your soil tends to be more sandy, it will feel gritty, drain quickly of both water and nutrients, and warm up quickly in the spring. With sandy soil, your garden may benefit from the careful addition of small amounts of clay that are WELL worked into the soil. Lumps of clay will remain lumps of clay so be sure there are no lumps, and be sure to mix it thoroughly into your soil. Compost will also definitely help, but it will be short-term help until the percentage of organic matter increases significantly.

If your soil tends to be more clayey, it will be heavy, smooth to the touch, and will easily hold the shape of a ball when dampened and rolled in your palms. It will be slow to absorb moisture, slow to drain, but generally very fertile. The addition of lots of compost and maybe very small amounts of clean sand can improve your garden drainage. Remember, too much water in the soil can rot roots, prevent appropriate gas exchange in the root/soil area, and encourage fungus.

If your soil tends to be more silt, what luck! Silt soils tend to feel rather silky to the touch. Adding compost is probably about all you’ll need since silt holds water and nutrients better than sand, and drains better than clay.

Oh, and have I mentioned that compost also helps to balance the pH of your soil?

Now for the at-this-point perennial question…

How much compost or mulch should you use?

As much as you can afford!

Even “free” compost has a cost in terms of your time and energy, but it can potentially be a valuable asset to your garden, saving you both time and money in the future.

“If I wanted to have a happy garden, I must ally myself with my soil; study and help it to the utmost, untiringly. Always, the soil must come first.”
~Marion Cran, If I Where (sic) Beginning Again (quoted on http://gardendigest.com/earth.htm)

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One thought on “The DIRT on DIRT

  1. Pingback: USDA Hardiness Zones | My Musings on Many Things

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