Why Raised Garden Bed Soil Health Is So Important

Why Raised Garden Bed Soil Health Is So Important

Soil is the anchor for raised garden beds to hold and feed plants. Soil by itself doesn't really provide nutrients to plants as they are commonly understood. Instead, soil is the environment that promotes healthy ecosystems below the surface—it promotes (or hinders) the ability of plants and their roots to use air, water, and nutrients at optimal levels.

As gardeners, we can design raised beds of soil to maintain proper hydration and create an environment that supports countless life, called a soil food web.

A healthy soil food web is filled with billions of microbes and larger organisms, such as earthworms, working together. Healthy soil promotes the process of nutrient development and delivery (to plants).

In other words: don't feed the plants. Feed the soil so it can feed the plants.

Soil food webs are complex, so building a healthy ecosystem doesn't mean going to the home improvement store and buying lots of bags of garden soil to fill up all your raised bed space. Sure, you can go this route, but it'll be expensive, and it won't give you a robust growth medium. You have established a healthy growth medium.

Build Your Garden Soil

Over the years, I have developed a variety of elements that have brought me a wealth of gardening success. The method I describe here is not like a soufflé recipe. I wouldn't tell you to have to add a teaspoon of this or 12 oz. that. My method - like my soil - is organic. Every time I follow it, it's different. These are estimated percentages that work well for me, but they don't need to be accurate.

I use a mix of organic materials to create diverse mixes. As mentioned earlier in this series, your soil is not an area where I would recommend cutting corners when it comes to cost. One of the things I learned early on is that you get what you pay for. Your biggest investment is in your land. Plant health and crop success depend on it.

Don't expect perfect soil in your first year. Building good soil is a process that spans the growing seasons. The method I describe here for you will build a healthy soil foundation that will develop rich soil in the coming seasons.

I do recommend mixing all the ingredients together when you initially fill the raised bed. Combine it well so that the elements can introduce each other appropriately. When I get into soil maintenance later, you'll see why I don't mix established soil, but to "get the party started" - mix everything up and mix well.

The American Compost Council encourages all gardeners and growers to "Go for Five." This refers to a target of 5% (by weight) of the total organic matter in the soil.

A rough estimate to make this 5% happen is to include about 30% of the total volume of organic material. All references here are by volume and - again - are only approximations. So, with that in mind, this is how I achieve these magic percentages:

50% Premium Topsoil: This makes up the bulk of your bed.

Buy topsoil in bulk or in bags. If you're buying in a bag, buy a trusted brand and check the ingredients, which are often regionally sourced.

If you need more than half of your pickup truck load, I recommend buying in bulk. Find a reputable landscape supplier by getting referrals. If you don't know someone who can offer a referral (or even if you do get a referral), take the time to talk to the provider. Ask questions about what to make of topsoil. I even checked it by smelling it and squeezing it (well, as we all know, I also taste test it once in a while).

A squeeze test is just taking a handful and squeezing it. It should stay together, but when you run your fingers through it, it comes apart easily. If it's sticky or hard to separate, it's too heavy. First, too much sandy soil won't hold together.

A good topsoil should not be sticky or sandy. It should lean toward the darker side of brown versus gray or clay color, and should smell earthy—not rancid.

Note that I check bagged soil the same way. I never open the bag. I look for a bag that has been torn open - usually there is at least one.

When in doubt, look for certification marks from some nationally recognized organizations that indicate the soil contains certified compost. Using certified compost as an ingredient, you can be confident that the quality of the topsoil will also be good. You don't want to make the same mistake I did - not checking the quality first and then not delivering it home. I found a pile of fill on my property - not the topsoil I ordered.

It's not uncommon for suppliers to provide fill soil as "topsoil," and you don't want to start your bed with fill soil.

30% High Quality Homemade or Certified Compost: Use what you can, but get the difference from a reputable supplier.

I do a lot of compost at home but not enough. Therefore, you will most likely also need to purchase more compost than you can produce. Not all compost is created equal.

My advice is to do your homework. Suppliers may have some printed information about their products. If not, please take the time to talk to the supplier here as well. Ask questions about what to make of compost. Questions like this:

Where do their ingredients come from?

What materials do they accept?

What do they not accept?

How do they make compost?

Your common sense will help you identify any red flags. Don't be afraid to leave a vendor who can't provide good answers. Composting is an investment, so choose wisely.

An easy way to make sure your compost purchase is safe is to find a supplier that offers certified compost as recognized by the American Compost Council. Their website has some solid advice and a database of composting members. This is how I buy bulk compost and I've never been disappointed.

Top six organic materials to add to topsoil and compost:

Leaves: Aged, chopped leaves are one of my favorite additions. They're free (I'm a frugal person, so I like that), and they add a lot. So what do I mean by old age? I chop up the leaves, moisten them, and within six months to a year they are rotten and ready to be combined.

If you don't have enough leaves, ask around. I guarantee friends and neighbors will be happy to share their supplies.

Mineralized Soil Mix: In another case, it was important to find a good landscape supply company. Years ago, I discovered the value of adding mineral-laden soil. It has had a noticeable impact on the success of all the plants in my garden.

Minerals are the most important ingredient that no one seems to talk about much. You can learn more about mineralizing soils in my podcast.

Mineralized soil mixes are widely available and are usually sourced locally; so its makeup will depend on your region. Granite is found everywhere in the Atlanta area, so most mineralized soil mixes here are made from granite dust. Azomite is another common and good option.

Vermicompost (Worm Castings): When I added worm castings (aka worm manure), I noticed a huge change in my garden. Buy it if you can find it in bags or bulk. Although it's not easy to get and it's not cheap; it's well worth it. Fortunately, a little goes a long way. You don't need much to make a big difference.

Worm castings are significantly higher in all the major nutrients plants need to thrive. In fact, worm castings have five times more nitrogen, seven times more phosphorus and ten times more potassium than regular topsoil.

Castings add a layer of complexity to the overall soil composition. Just say. . . Enough is enough; this medium is one of my secret weapons for creating high-yielding garden soils.

Mushroom compost: This dark brown, pliable organic material is not made from mushrooms.

It's a by-product of the ingredients in which the mushrooms are grown - what's left over after the mushrooms are harvested.

Mushrooms are grown in a mixture of natural materials such as hay, gypsum, corncob, cottonseed husks, etc. But when the material is composted, bagged and sold as mushroom compost; it's light and crumbly. It contains about 3% nitrogen and potassium, a little phosphorus and other extra elements like magnesium and calcium. Since it's a neutral pH (6.5-7.0), it won't have an impact on your soil pH.

Ground Bark: There are a variety of ground bark to choose from, but pine is the most common. Although pine bark is slightly acidic, I have never found it to have much of an effect on the overall pH of my garden soil. Make sure to use aged bark in this application. During the initial decomposition process, the freshly chopped wood will be plundered from the soil rather than beneficial to the soil.

Ground bark is a good source of carbon. It breaks down over time, and its rough texture provides room for the movement of water and oxygen through the garden bed. Topsoil, compost, and most of the other ingredients I list here have similar textures. Ground bark brings a variety of particle sizes that can really enhance the health of your plants.

Composted cattle or poultry manure: Fully composted animal manure has been a mainstay of organic soil fertility for thousands of years because it adds nutrients, organic matter, and variability in particulate matter to complement the overall soil composition. That hasn't changed. What has changed are farming practices and the resulting risk of manure.

Compost fertilizers added to today's garden soils may contain synthetic herbicides that are still effective, even in well-composted manures. For this reason, I recommend that you use cow or poultry manure rather than horse manure.

Buy composted cow or poultry manure by bags and trusted sources. Buyers beware if it's a non-branded item or if you're buying in bulk. Many people have poisoned their soils with deadly compost (including me), inadvertently adding herbicide-contaminated ingredients commonly found in horse manure.

I no longer add horse manure - because horses are more likely to consume hay from fields sprayed (or oversprayed) with persistent herbicides. Persistent herbicides don't break down for years. It passes through the horse's digestive system and goes through the composting process without losing any lethality. Traces of herbicides, however tiny they may be, will kill or wreak havoc with the normal growth habits of many garden foods, which are as effective after composting as they are the day they were made.

There may be a source of horse manure that you actually want to use. In this case, you can do a biometric test. Do this simple test before letting manure come into contact with plants, soil, or compost. I didn't biometrically test my GardenFarm's horse manure, and I suffered four years of consequences as a result.

These are the "ingredients" I use. Here are the ingredients I don't use:

Horse manure: Worth repeating. If you want to use horse manure, be sure to check out the link for biometric testing. That little bit of time can save you years of grief.

Sphagnum moss: This may come as a surprise. However, peat moss is not a sustainable material. It takes hundreds of years for peat to develop in peat bogs.

Did you know that peat moss can destroy the ability of soil to absorb water? Ironically, it's often recommended for its water-retaining ability. It can help retain water, but once the peat moss dries, it can be difficult to rehydrate. Have you ever watered a container that has dried up but the water just rolls off the surface? Usually, this is due to peat moss in the container soil.

Faux Fillers: While it may be tempting to take up space with fillers when you're first building those raised beds, I recommend against using them. Although they may save you some initial cost, even organic fillers can be problematic. Over time, they will break down and the surface of your garden bed will sink, requiring you to add more soil later.

On top of that, the filler blocks drainage. I know, it's counterintuitive, but research has proven it. I executed my test using the container so you can see it for yourself. Whether in a small space like a shipping container or a large space like a loft bed, the science is the same.

Filling in dirt: This can also be a tempting way to save money, but it can get in the way of all your other efforts to build a healthy growing environment.

What is fill? It's what lies beneath the first few inches of dirt on the ground. The first layer of the earth is the topsoil; it is naturally formed—with varying degrees of health—organic matter, light and air, and other good things that happen naturally near the surface. The fill lies below the topsoil and does not include the good qualities inherent in the topsoil.

Some additional materials worth considering as additives:

Biochar: I've heard good things about Biochar. I've only recently started adding it to my garden, so it's too early to give you any personal opinion. Biochar does have some nutritional value. It's a pure carbon source that doesn't break down, but it does help make existing soil nutrients available to plants.

Fire ash: I recommend not putting any fire ash directly into your garden bed. If your fire ash is all woody, it can be a good addition (in small amounts) to your compost. Do not use charcoal ash as it may contain some ingredients that are not good for your organic garden.

Mycorrhizae: This fungus is very popular as a soil component in bagged products. Healthy native soil usually already has this fungus (but don't use your native soil in your bed). Adding mycorrhizae to the soil may offer benefits. It doesn't do any harm anyway.

Like containers, raised beds leach nutrients faster; therefore, as a last step, it's a good idea to add some slow-release, non-synthetic, nitrogen-based fertilizer (like Milorganite) to the mix. It's like a cup of cocoa powder on top of a latte - with a little extra kick.

maintain healthy soil

Building your initial raised bed garden environment with quality ingredients will give you good results in the first season. However, those crops you grow will continually extract nutrients from these beds.

Just like your bank account, it is critical that deposits keep up (or better exceed) your withdrawals. How do you do it? Amend the soil once or twice a year with organic nutrients (like the ones I described above) instead of synthetic fertilizers. By modifying your garden beds, you will see better soil in the second season, rich soil in the third season, rich soil in the fourth season, and so on.

Good soil is like fine wine; it gets better and better over time.

Before you amend your soil for the first time and approximately every two seasons, I recommend doing a soil test. You can contact your local county extension office, testing is very cheap ($20-30). A soil test will determine soil pH and deficiencies to help guide your correction choices.

When the soil is at neutral pH, the nutrients you provide to the soil will be optimally absorbed by the plants. Therefore, it is important to understand when and how your soil pH shuts down and how to rebalance it.

Sometimes, I gently scrape the compost onto the bed surface, but I usually just put the compost on top, put the mulch on it and walk away. Why? Remember the microbial party we started when we first built bed soil? Well, all these microbes are getting along just fine right now, and they can't wait to see more. So they naturally and quickly throw all their compost back into the party with everyone else.

If I "disrupt the party" by plowing in my compost, I will

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