Joe Lamp’l, is host of GardenSmart on PBS, author of Over the Fence with joe gardener®, syndicated columnist and founder of, providing smart resources for gardeners everywhere.

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Creating Great Soil in Your Garden
by Joe Lamp'l       #Soil

A few years back, I was faced with the task of setting up a brand new garden from scratch. Normally, that sort of a challenge wouldn’t even raise an eyebrow, but this wasn’t just any garden. It would be our new set for all the vegetables and plants grown for the national television show I was hosting at the time. 

The homeowners of our existing garden informed us that they would be moving soon. My heart sank upon hearing the news. My first thought was how to salvage all the garden soil I had been cultivating for the past two years. 

This soil was in its prime, alive with beneficial microbes and nutrients and balanced with just the right combination of sand, silt and clay. Since my soil was the real star of the show, I thought about relocating it to our new garden. But how would I do that on a TV budget that had no room for such extravagance? 

As the reality sunk in and plan A (moving the soil) was eliminated, it was time for plan B. In a new garden from scratch and without any appreciable soil to start with, I concluded that I would have to create it quickly, in the volume I needed, and still be sure that it was productive enough to ensure a fast start and a strong finish. Failure is not an option in a TV garden. This soil had to be perfect. 

I thought about all the soil components that had worked so well in the past: great drainage, moisture retention, ideal structure, texture and tilth and plenty of organic material and nutrients. I rolled up my sleeves and crafted my list of soil amendments that would go into my new garden beds. 

Topsoil (65%)
My first specified ingredient was topsoil. I was careful to ensure that I was not adding fill dirt ­— although it’s much cheaper, fill dirt is heavy on clay, light on nutrients and poor in structure. True topsoil, on the other hand, is taken from the top several inches of earth and contains the greatest amount of organic matter.  

Compost is the best amendment that you can add to any soil. It adds life and fertility, improves drainage and moisture retention and — the best part — you can make it yourself. Photo by Joe Lamp'l

Compost (10%)
Good old aged leaves, grass clippings, cuttings, kitchen scraps, paper bags, etc. — I still find it amazing at how benign raw material can combine to create such a potent soil amendment in the finished product. I make my own, and I prefer it that way. You can purchase compost products, but you never really know what’s in them. 

Properly made compost contains all the microorganisms and organic matter that support a healthy and diverse soil food web, the essence and ultimate goal of creating healthy, living soil. Compost alone is an excellent soil amendment but a little goes a long way. 

Worm Castings (10%)
Although the politically correct terminology may be castings or vermicompost, in reality, it’s just “worm poop.” But, oh, what a fabulous impact it has in the soil! The actual casting contains thousands of beneficials microbes and a byproduct called humic acid. It’s the glue that helps important nutrients bind together in a form that is available to plant roots on demand. 

Worm castings contain five times the available nitrogen, seven times more potassium and nearly twice the calcium compared to topsoil alone. What’s more, worm castings improve moisture retention and are non-burning to plant roots, no matter how much is used. 

Finely ground pine bark mulch (10%)
Mulch of this type ensures the soil has plenty of space for drainage and air. Both are essential to healthy root establishment. I chose pine bark as opposed to hardwood mulch because it breaks down faster while contributing additional nutrients. 

Composted Cow Manure (5%)
There are many bagged brands on the market. I spent a little extra to get 100% composted manure, which is non-burning. It adds bulk to sandy or light soils, improves structure, moisture-holding capacity, helps break up compacted soil and contains beneficial microorganisms and nutrients. You can spend less, but it includes a lot of cheap fillers. I don’t recommend it. 

Organic Minerals and Nutrients
To round out the mix, I added small amounts of some of my favorite organic supplements. A little goes a long way:

Blood meal: A good source for slow-release nitrogen 
Bone meal: An excellent and long-lasting source of phosphorus     
Greensand: An excellent soil conditioner for both sand and clay and a good source of potassium
Dolomitic limestone: An important supplement to raise the soil pH, if necessary; provides the added benefit of calcium and magnesium 

Soil that contains the right amount of nutrients, retains adequate moisture and allows plant roots to spread effortlessly gives them the best opportunity for vigorous development. Photo by Joe Lamp'l.

Amazing Results

In the end, I am happy to report that this garden was my best ever. In fact, the results were quite amazing, especially in light of the extremely challenging conditions we experienced that season.  

This is a formula that I continue to use with great results whenever I’m faced with building a new garden or amending an existing one. Similar results can be achieved in your garden by working with the soil you already have, regardless of its present condition.

Improving Existing Soil: 

Understanding three commonly used gardening terms — texture, structure and tilth 

Texture: Texture refers to the relative percentage of sand, silt and clay. When these three are equally proportionate, the soil is said to have “good texture.” Another term used to describe the same concept is “loamy.”  

Structure: Structure refers to how soil binds together and the shape that the soil takes based upon its physical and chemical properties. Simply put, structure is how the sand, silt and clay fit together. Good structure is evident when the soil holds together if squeezed, but breaks apart or crumbles easily when disturbed. 

Tilth: When a soil has good tilth, it drains well, but not too well. It is loose enough to allow for adequate drainage, yet dense enough to retain moisture long enough for plant roots to utilize it. This is why garden soil should neither contain too much sand nor clay.

What Kind of Soil Do I Have?  

A simple jar test will give you important clues as to the structure of the soil you have naturally and a starting point from which to begin your soil “makeover.” Photo by Courtenay Vanderbuilt

The Jar Test: Find a jar with a tightly fitting lid, such as a mayonnaise or Mason jar, and fill it about half way with soil from your yard or garden. Add water to the jar until it is almost full. Secure the lid, and shake the jar vigorously. Set it down, and let the contents settle overnight or longer. What you will find is that the soil has separated into three distinct layers.  The first layer is sand. These are the largest particles. Because they are the heaviest, they settle to the bottom first. The second layer is silt. Silt is a combination of sedimentary materials that are smaller than sand and larger than clay. Therefore, silt settles next as the middle layer. The third layer is clay. It is the finest and lightest of the three most solid components of soil.  Now you can easily see the proportions of just how loose and sandy or dense and full of clay your soil is. More importantly, this will give you the clues for how to approach amending it for ideal conditions.  It’s important to have all three types of particles in your garden soil. The different sizes of each create essential space for air and water to exist as well. Imagine basketballs, tennis balls and marbles, all sharing the same space. It’s easy to see how air and water can find their way in and through the spaces in between. 

The Squeeze Test: Regardless of the current soil structure, you can change what you already have. The goal of amending soil is for it to pass what I call the “squeeze test.” If you were to squeeze a handful of ideal garden soil, it would bind together and hold its shape. However, it would also be loose enough so that by running your fingers through it, the lump would crumble or break apart easily.  

Improving sandy or loose soil: In sandy soil, water and nutrients pass through the root zone so quickly that plants don’t have sufficient opportunity to absorb them. The goal is to increase its water and nutrient-holding capacity. Adding organic material helps the sandy particles stick together into aggregates of various sizes. The net effect is that water and nutrients have a chance to bind to these aggregates rather than quickly leaching them out. Peat moss and compost are common amendments for improving sandy conditions, but any organic material will help.  

Improving dense or compacted soil: Soil that is too dense or compacted retains too much water and too little air. Here, the goal is to loosen it. Adding organic material, such as composted bark, wood chips, composted manure, shredded leaves or compost, helps to achieve the proper balance. In dense soil, the addition of organic material of various particle sizes allows the smallest particles of clay to separate from each other and bind to the larger particles. These resulting aggregates create more space for air and water, which promotes soil health. However, do not add water-retentive materials, such as peat moss.

From State-by-State Gardening September 2012. Photos by Joe Lamp’l and Courtenay Vanderbilt.


Posted: 09/26/12   RSS | Print


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