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Preparing Garden Soil for Planting: Soil Amendments, pH, Nutrients, and More | The Old Farmer's Almanac

Dig in the Dirt! Soil Preparation: How Do You Prepare Garden Soil for Planting?

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Tips for Improving Your Garden's Soil Quality

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If your plants don’t thrive, the answer is often in the soil. Healthy garden soil makes healthy plants that are less vulnerable to pests. 

The good news? You can improve your soil! Here is a 3-step quick fix to healthy soil and a guide on soil health for those who wish to “dig deeper.” 

Three Easy Steps for Soil Preparation

The last thing we want to do is overwhelm the beginner gardener! If you do nothing else, here are three basic steps you can do before planting.

  1. Clear out rocks and debris: To dig up grass, use a spade to cut the sod into small squares and pry from the planting area with the end of the spade.
  2. Loosen the soil: If it’s your very first garden, loosen the soil to a depth of at least 8 inches (12 is better) so that roots can reach down.
  3. Add Organic Matter: Compost and aged manure not only feed the soil with nutrients but also drains well, loosens the soil to create more oxygen for plants, and stabilizes and anchors plant roots. Spread at least 2 to 3 inches of compost or aged manure onto your soil (no more than four inches).
    If it’s your first garden and you need better soil, we recommend working in the compost. If your garden is established, we recommend a no-dig approach and leaving the compost on the surface. This exposes fewer weed seeds and does not disturb the soil structure. Let the worms do the digging in for you! 

    Level the garden bed: With a steel garden, rake or hoe the surface so it’s level. 

A tip: If you live in a colder region, consider a raised garden bed to help wet, cold soils dry out and warm up more quickly. Also, cover your beds before planting with black plastic to cardboard to block light and protect them from snow, rain, and erosion. Read more about warming up the spring soil.

A tip: If you have a very weedy garden and are just getting started, cover the soil in late winter with clear plastic (“solarization”). Once the weed seedlings are up, pull them out or remove them with a hoe. Don’t dig up the soil, which will just bring new weed seeds to the surface—the idea is to remove those already at the top. Once you build a rich, dark, fertile soil foundation, gardening will be “easier” the rest of the year and going forward! 

Digging Deeper: Know Your Soil

Do you have clay or sandy soil? Is your soil acidic or alkaline? Is it thin or rich in nutrients? If you really want to improve your gardening success overall, take time to understand the type of soil in your own yard. Determining the makeup of your soil composition is important because you’ll understand if you need to tweak anything. Having good soil is critical in your success as a gardener and will end up making gardening so much easier. 

We’ll touch on three important components:

  1. Soil Type
  2. Soil pH
  3. Soil Nutrition

I. Soil Types

There are three types of soil: clay soil, sandy soil, and silt. 

The ideal soil texture is “loamy” and consists of equal parts of sand, silt, and clay. Loamy soil has that perfect balance—it holds moisture but also drains well, allows oxygen to reach plants’ roots, and is rich in humus (organic matter). It’s fertile, easy to work, and contains plenty of organic matter.

the soil texture pyramid from the USDA
Soil Texture. Credit: USDA

Loamy Soil (the Goal)

The soil is damp but not sticky, even after a rainfall. Good garden soil crumbles easily. It will not form a hard ball when squeezed nor crack or crust over when dry.

Loam soil, ideal for planting
Loam for planting. Credit: Kram9/Shutterstock

Clay Soil 
With very fine particles, clay soil will feel wet and sticky. Clay soil will easily hold its shape when rolled into a ball. It has poor drainage and poor aeration. It’s often fertile, but the nutrients get locked up. When it dries in the hot summer sun, clay soil cracks; it also gets waterlogged in winter. Clay soil needs lots of organic matter and loft to break up the sticky, dense texture, including compost and well-aged manure.

Clay soil in a garden bed
Clay soil, one of the most challenging types of soil, needs a lot of organic matter!

Sandy Soil 
With its large particles, sandy soil feels gritty. It’s a loose and crumbly soil and won’t stay in a ball. Sandy soil drains very quickly and leaches nutrients, so it is not very fertile. You’ll need to amend with compost and well-aged manure.

sandy soil in a garden bed
Sandy soil. Credit: T. Tea/Shutterstock 

Test Your Soil

To better discern your soil type, you can have it tested. Many universities have affiliated Cooperative Extension services, which will often test your garden soil for a small fee.

Or you can also conduct a DIY jar test to determine your soil type. Get a glass mason jar and put a couple of inches of soil in the jar. Do this with several jars, taking samples from around the garden. Then simply fill the jars with water. Here are the complete instructions for the jar test and other DIY soil tests

a shovel in the soil in a garden bed and soil

II. Soil Nutrition

A soil test will also tell you more about the fertility of your soil. Without fertile soil, it’s almost impossible to grow a vegetable garden. Plants’ primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). On the package of fertilizer, you’ll see these three values separated by dashes (N-P-K); the numbers of each nutrient indicate the percentage of net weight contained.

  • Nitrogen (N) promotes strong leaf and stem growth and a dark green color, such as desired in broccoli, cabbage, greens and lettuce, and herbs. Add aged manure to the soil and apply alfalfa meal or seaweed, fish, or blood meal to increase available nitrogen.
  • Phosphorus (P) promotes root and early plant growth, including setting blossoms and developing fruit, and seed formation; it’s important for cucumbers, peppers, squash, tomatoes—any edible that develops after a flower has been pollinated. Add (fast-acting) bonemeal or (slow-release) rock phosphate to increase phosphorus.
  • Potassium (K) promotes plant root vigor, disease/stress resistance, and enhances flavor; it’s vital for carrots, radishes, turnips, onions, and garlic. Add greensand, wood ashes, gypsum, or kelp to increase potassium.

→ Learn more about NPK Ratio: What Do Those Numbers Mean?

A soil test will tell you what nutrients your soil is missing. You do not want to add nutrients to your soil if they’re already available in high amounts; this may actually inhibit your plants’ growth.

For example, a soil test may tell you that your soil needs more potassium but absolutely no additional phosphorus. You’ll also learn about some other essential nutrients, including magnesium and calcium. 

III. Soil pH

Soil pH is the third and last component of healthy soil and affects the availability of nutrients and minerals in the soil, as well as how well a plant can access, absorb, and regulate these materials. A very high or very low soil pH will result in nutrient deficiency or toxicity, leading to poor plant growth.

A pH ranging from 6.0 to 7.0 is ideal for most garden vegetables. This is the ideal range when microbial activity is greatest, and plant roots can best access nutrients. However, many plants tolerate a wide range, and certain plants have specific pH range preferences. Find a list of common garden plants and their pH preferences here.

Availability of Nutrients at Varying pH Values

Availability of nutrients at different pH levels. Image by CoolKoom/Wikimedia.
This chart shows the availability of nutrients at different pH levels. Slightly acidic soil (6.0–6.5 pH) is best for most plants. Image by CoolKoom/Wikimedia.

Through a soil test, perhaps you find out that your soil is too acidic (which is great for blueberries and azaleas, but not cabbage). Your soil test results will make recommendations to adjust your soil pH.  If your soil pH is too low (acidic), add garden lime to the bed. If your soil pH is too high (alkaline), add powdered sulfur to the soil.

Raising and lowering your pH does take time; once lime or sulfur is applied, it can take a year or more to see any movement in pH. Remember, you do not have to change your soil pH if you grow plants that tolerate the current pH of your soil. And never assume that you should add lime, sulfur, wood ash, or other amendments. Don’t make already alkaline soil even more alkaline with wood ash!

Ready to Improve Your Soil?

As discussed above, the best way to make poor soil into perfect soil is to add nutrient-rich organic matter such as compost, aged manure, or leaf mold.

The benefits of organic matter are countless! Adding organic matter…

  • …loosens tight clay soil to improve drainage and aeration and release minerals.
  • …bulks up sandy soil to improve its water-holding capacity and nutrient retention.
  • …makes soil easier to dig and work with.
  • …moves soil pH towards a level ideal for most fruits and vegetables.
  • …provides a slow-release form of fertilizer across the season, reducing reliance on commercial fertilizers.
  • …supplies food for beneficial soil organisms (earthworms, insects, fungi, and beneficial bacteria), which not only convert organic matter into nutrients for plants but also aerate the soil.

Common Soil Amendments

Here are some of the most common amendments and their functions:

  • Plant material: Leaves, straw, and grass clippings. Work material into the soil several months before planting to allow it time to decompose. 
  • Compost: Decayed plant materials such as vegetable scraps. Work it into the soil at least a few weeks prior to planting. Excellent soil conditioner that adds nutrients. It may also lower soil pH.
  • Leaf mold: Decomposed leaves that add nutrients and structure to the soil.
  • Aged manure: A good soil conditioner. Use composted manure and incorporate it into the soil well ahead of planting. Do NOT use fresh manure in vegetable gardens, as it can damage plants and introduce diseases. Note: Manures contain a higher concentration of salts, so use them more sparingly than you would other organic amendments, particularly in dry regions where salts won’t be leached away by rainfall. 
  • Coconut coir: A soil conditioner that helps soil retain water. This material is a more sustainable alternative to peat moss.
  • Bark, wood chips, and sawdust: These materials should be composted before being added to garden soil. Otherwise, they will rob the soil of nitrogen and, consequently, starve the plants of this essential nutrient.
  • Cover crops (green manure): Cover crops are more of a soil improvement technique than a soil amendment. Cover crops (such as clover, rye, or oats) are planted in the garden at the end of the growing season. They grow rapidly in the fall and are then worked into the soil in the spring. They often contain an abundance of nutrients, and their roots can provide structure. Read more about using cover crops.
  • Topsoil: Usually used with another amendment to provide volume. Replaces existing soil.
  • Lime: Raises the pH of acidic soil. Only use if recommended by a soil test.
  • Sulfur: Lowers the pH of alkaline soil. Only use if recommended by a soil test.
  • Wood ash: Raises the pH of acidic soil. Only use if recommended by a soil test.

When to Add Organic Matter

Adding organic materials in the fall allows time for them to decompose and break down over the winter. Soil high in organic matter releases a reservoir of nutrients that are slowly released over time, which improves root growth and biological activity.

If you didn’t get to this job in the fall, amend it in the spring as soon as the soil is workable.

How do you know when the soil is workable?

Take a handful of soil from a depth of about 6 inches and squeeze it in your hand to form a ball. If the soil crumbles through your fingers, then it is dry enough to work. If the soil forms a ball that falls apart on its own or when you press it with your thumb, then the soil is dry enough to work. However, if the ball retains its shape or your thumb just leaves an indentation, the soil is too wet to work. Wait a few days and check the soil again. 

To add organic matter:

  1. Pour enough organic matter into your garden so it can be spread to a depth of at least 2 inches. Do not add more than a 4-inch layer. With a garden fork, mix the organic matter into the top 6 to 8 inches of existing soil. Make sure it is well combined and spread evenly!
  2. Continue to add organic matter each season during soil preparation to build and maintain the soil. Be patient; it may take several seasons of amendments until the soil is loamy.
  3. After amending the soil, it’s best to water well and then check the soil moisture.
  4. Let a window of at least two weeks pass between when you add organic matter and when you plant.
  5. Before planting, rake the soil clean and level it. Remove all fallen sticks, rocks, and other materials. Now, you’ll be ready to plant!

Fixing Different Soil Types

Remember, before adding any amendments, it’s a good idea to get a soil test done! Here’s how to tackle each type of soil:

  • Sandy soil: Work in 3 to 4 inches of organic matter (such as compost or well-rotted manure), as well as a material such as coconut coir, which will help with moisture retention. Mulch to retain moisture. In subsequent years, mix 2 inches of compost into the soil each fall. Using cover crops and then working them into the soil can also help to provide structure in sandy soils. 
     
  • Clay soil: Start by adding 3 to 4 inches of compost to make it more workable. Each year thereafter, mix an additional 1 inch of compost into the soil in the fall. Fibrous materials such as straw or fine bark mulch will add more structure to clay soils, too. Contrary to popular belief, amending clay soil with sand will only result in tough, concrete-like soil! Minimize tilling when dealing with clay soil, too. Or, just garden in raised beds! â†’ Read more about gardening in clay soils
     
  • Silty soil: Silty soils hold water and nutrients but are more susceptible to erosion. If you have silty soil, add 1 inch of organic matter every year to improve the texture. Avoid tilling as much as possible and compacting the soil. Or, just use raised beds. 
     
  • Loam: Loam is the ideal mix of all three soil types and will likely not need significant amending to get it ready for planting. Nevertheless, if a soil test does show a lack of nutrients, adding organic matter will improve the soil and give your plants a boost.

Too Much of a Good Thing

As with anything, adding too much organic matter can be detrimental! Too much organic matter can rapidly increase microorganism activity, which uses up available nitrogen and affects soil pH. Aim to have organic matter make up about 1/4 of your soil mixture overall, and thoroughly mix it into your existing soil.

A Note on Raised Beds

If you’re struggling with your soil, another option is raised garden beds. With raised beds, you control the soil that you put in the bed. Whether you decide to plant directly in the ground or in a raised bed, make sure that you don’t walk on your newly amended soil, or it will get compacted. The general rule is to make sure a bed is no wider than four feet—or has a garden path—so that you don’t walk on the soil. See how to build a raised bed.

Raised beds also help in colder climates to advance your growing season by a couple of weeks. Speed things along by covering the beds with something light-blocking and non-porous, like black plastic anchored down with rocks. If you’re not keen on plastic, you could lay old salvaged windows over the bed. At a minimum, we like to cover our beds with cardboard or old carpet remnants to keep weeds from growing.

Do you have an over-spent or neglected field you want to turn into a garden? Read our article about reclaiming your garden soil.

About The Author

Catherine Boeckmann

Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann

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