Tips for Great Soil Composition

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Soil is a living thing, and like all living things, it needs to be fed in order to feed our plants in turn. And much like in our food supply chain, there are numerous options when it comes to feeding plants and the soil. 

When talking about soil and plant health, we often talk in terms of NPK. But what is this? NPK is not one thing, but in fact three. The N stands for nitrogen, which is responsible for promoting green growth – think leaves and grass (which is primarily leaf). The next letter, P, stands for phosphorus. This helps promote bulb development (important for onions and garlic, as well as tulips and daffodils), root growth (all veggies really, but carrots and other root crops in particular), promotes flowering and fruit set (tomatoes), and disease resistance. Finally, K stands for potassium which promotes overall vigor, fruit ripening, and disease resistance.

Soil Macronutrients

• N (nitrogen): promotes green growth
• P (phosphorus): promotes bulb development, root growth, flowering and fruit set, and disease resistance
• K (potassium): promotes overall vigor, fruit ripening, and disease resistance

Soil testing

When we first started our garden beds, we tested the soil in our yard to learn what macronutrients might be in short supply. Not only did the test provide us with information about the macronutrients, but we also received information about our soil’s pH level…or how acidic it was. While it’s been so long ago I do not remember the numbers, I do recall that my dream of having a blueberry bed, which requires acidic soil, was going to take a lot of work and a special location if I wanted it to succeed. 

Taking the soil sample was pretty easy. We started by digging up some dirt from around the yard, which we then mixed together and filled into the sample bag for sending to the lab. Everything we needed we were able to get from our local County Extension office, along with instructions on how to proceed. We made sure to send in samples from around the yard, as well as a separate sample from the garden bed area. Ideally this process should be repeated every few years depending on how intensively the area is gardened. The reason they suggest periodic testing is so you know if you are over or under fertilizing and can adjust accordingly. In truth, we have only tested once. 

If you’re not certain whether you should test or not, go ahead and do it. The tests are not terribly expensive (roughly $20 here in Wisconsin), and provide a wealth of data. Still not certain? Take a look around your yard at your existing plants and lawn. Assuming you’re not in any kind of drought, do your plants look to be thriving? If not, or if your lawn and leaves are turning yellow, which could be a sign of iron deficiency, go ahead and test. Iron deficiency can be remedied by fixing the pH of your soil. If your plants look healthy and strong, skip testing.

Once we received our soil test, we learned that we have typical Wisconsin clay soil, and truly didn’t lack any major nutrients. This was not a huge surprise, as our neighborhood was pretty new, we were the first owners of the home, and the neighborhood had previously been farm fields. A fact that is confirmed any time we dig far enough down to expose the former field and get a waft of manure. 

The Soil Buffet

Even though we knew we had a good base, we still needed to feed the soil. Especially since we knew we would be planting rather intensively to increase output from the garden. When it comes to feeding time for your plants and soil, life can get a bit overwhelming. Organic? Inorganic? Spray? Powder or pellets? Compost? And if compost, what kind? For us the answer was easy. We wanted to be as organic as possible, and preferably as self-sufficient as possible. That meant, ultimately, we would rely primarily on compost. 

Compost can be a bit of a jungle, as it comes in many different “flavors”. If you are buying bags of it at your local nursery you may see things like mushroom, leaf, manure, etc. If you are buying in bulk from a local source you may also be presented with numerous options. At the end of the day the most important thing to be certain of is that the compost is well aged…particularly if you are buying from a local farm. If the composted manure is less than a year old it can still be hot and will burn your plants. What this means is that the compost contains far more nitrogen that your plants can handle, along with a great deal of ammonia, which both work to dehydrate the plants. If it still smells like, well, manure, set it aside for 3-12 months to cool down and decompose. When it no longer smells like manure it should be safe for the plants.

Types of Compost

• Leaf
• Mushroom
• Farm – horse, cow, chicken
• Home compost
• Vermiculture (worm compost)

Here at the Suburban Farmhouse, we’ve used a variety of compost all depending on what we can get our hands on. We’ve purchased aged compost from farmers, leaf compost and blends from landscaping companies, and even made our own. Currently we are working hard to become more self-sufficient with our compost by increasing feeding of the worms in our indoor vermiculture farm, as well as by improved management of our yard and kitchen waste in our outdoor compost bins. Our hope is that by next year we will no longer need to buy compost to feed our gardens but can use what we produce right here at home.

-Kim