What Is Garden Soil – When To Use Garden Soil

What Is Garden Soil – When To Use Garden Soil

By: Darcy Larum, Landscape Designer

At the start of the gardening season, garden centers, landscape suppliers and even big box stores haul in pallet after pallet of bagged soils and potting mixes. As you browse these bagged products with labels that say such things as: Topsoil, Garden Soil for Vegetable Gardens, Garden Soil for Flowerbeds, Soilless Potting Mix or Professional Potting Mix, you may begin to wonder what is garden soil and what are the differences of garden soil versus other soils. Continue reading for the answers to those questions.

What is Garden Soil?

Unlike regular topsoil, bagged products labeled as garden soil are generally pre-mixed soil products that are intended to be added to the existing soil in a garden or flower bed. What’s in garden soil usually depends on what they are intended to have grown in them.

Topsoil is harvested from the first foot or two of the earth, then shredded and screened to remove stones or other large particles. Once it has been processed to have a fine, loose consistency, it is packaged or sold in bulk. Depending on where this topsoil was harvested, it may contain sand, clay, silt, or regional minerals. Even after being processed, topsoil can be too dense and heavy, and lacking in nutrients for proper root development of young or small plants.

Since straight topsoil isn’t the best option for gardens, flowerbeds, or containers, many companies which specialize in gardening products create mixes of topsoil and other materials for specific planting purposes. This is why you may find bags labeled as “Garden Soil for Trees and Shrubs” or “Garden Soil for Vegetable Gardens”.

These products consist of topsoil and a mixture of other materials and nutrients which will help the specific plants they are designed for to develop to their full potential. Garden soils are still heavy and dense because of the topsoil they contain, so it is not recommended to use garden soil in containers or pots, as they can retain too much water, do not allow for the proper oxygen exchange and ultimately suffocate container plant.

In addition to the effect on plant development, topsoil or garden soil in containers can make the container too heavy to easily be lifted and moved. For container plants, it is much better to use soilless potting mixes.

When to Use Garden Soil

Garden soils are intended to be tilled in with existing soil in garden beds. Gardeners may also choose to mix them with other organic materials, such as compost, peat moss, or soilless potting mixes to add nutrients to the garden bed.

Some commonly recommended mix ratios are 25% garden soil to 75% compost, 50% garden soil to 50% compost, or 25% soilless potting medium to 25% garden soil to 50% compost. These mixtures help the soil retain moisture but drain properly, and add beneficial nutrients to the garden bed for optimal plant development.

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What Is the Difference Between Potting Soil and Garden Soil?

Potting soil won’t work in your garden, and garden soil won’t work in your pots. Here’s why.

Bagged Compost

Bagged compost can be picked up from most garden centers, nurseries or box stores. The cost of bagged compost may be a bit higher than from other sources, because in addition to paying for the compost, you are also paying for the packaging and associated shipping costs. However, the packaging also makes it a bit easier to load and cleaner to transport home from the store than un-bagged compost.

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All soil is not created equal. The soil your tomatoes love will suffocate your succulents, and the soil that keeps your cactus in peak form will frazzle your ferns. Matching the right soil to the right plant and purpose is part of the secret sauce to keeping your plants gorgeous. So as you stand there in the garden center on Saturday morning looking at the bags of soil and wondering which kind to buy, know this: Garden soil won’t work in your pots, and potting soil won’t work in your garden. Here’s what you need to know about each.


Application as a Soil Amendment

The application of wood ashes as a soil amendment is not an exact science, and if used modestly, there is little likelihood of causing harm. A general rule of thumb is to apply a half pound each year to shrubs and a half pound per inch of truck diameter to each tree. For lawns and garden beds, ashes may be applied at a rate of 10 pounds per 1,000 square feet of growing area, says Oregon State University's OSU Extension Service.

Before you apply the wood ash, you'll want to sift it through a piece of hardware cloth to remove any large chunks. Spread the ashes evenly over the soil area and water thoroughly to wash the nutrients into the root zone. Compost piles can also benefit by sprinkling a cup of ashes into each layer of the pile.


Potting Soil Pros and Cons

Ilana’s viewpoint: Using garden soil is all well and good for outdoor garden beds and the like, but it’s just as important to learn about potting soil pros and cons and when to use potting soil for gardening.

Potting soil is better for containers. Potting mixes are typically composed of ingredients that hold onto water and nutrients, and others that promote good drainage and aeration. For example, they may contain peat, vermiculite (an expanded clay material), perlite, coconut coir, compost, or bark. Quality potting mixes are much less compactible than garden soil. These qualities help potted plants deal with the difficulties of life in a container.

Potting soil may be identical to potting mix, or it may contain actual soil as one of the ingredients. Read the label to know what you are getting. If soil is on the ingredient mix, the product is good for adding to outdoor raised beds or outdoor containers, but it’s not ideal for indoor container use. Soil-free potting mixes are best for most indoor plants, but they’re usually too light and fluffy for garden bed use.

Potting soil better fits specific plants. Many varieties of potting soil are available at gardening stores, hardware stores, and other outlets. These may be designed for different types of plants and situations. You’ll find cactus and succulent soil, mixes for acid-loving plants, African violet mixes, and water-holding mixes designed for people who frequently forget to water their plants.

Potting soils are easier overall. If you use garden soil for outdoor containers or raised beds, you’ll have to add a source of nutrients, and you may have to increase the percentage of organic matter, improve the drainage, or change the pH. To do that, you’ll probably have to buy several different amendments to mix in. On the other hand, potting soil and potting mixes are usually designed to be used right out of the bag. You can simply fill up the container and add the plant. Some potting soil mixes also include fertilizers, compost, worm castings, bone meal, or other ingredients that provide nutrients or improve the qualities of soil.

Fresh potting mix lessens chance of disease. Another of the top potting soil benefits is a lower chance of disease. This is especially true if the bag is labeled “sterile mix.” Sterile potting mix is great for starting seeds, since seedlings are especially vulnerable to disease. Look for mixes labeled specifically for seed starting.

Potting soil cons. The main disadvantage of potting soils is that it can be expensive, while soil from your own garden is free. Some plants can be harmed by a potting mix intended for another type of plant. Also, some potting mixes are not suitable for organic gardening because of synthetic ingredients they contain.

How Do Potting Soil Benefits Hold Up Compared to Garden Soil?

Potting and garden soils have very different compositions and, therefore, very different purposes. In most cases, garden soil is good for every outdoor application, while potting soil is best for indoor purposes like seed starting and growing houseplants. While potting soil has many benefits for container plants, the expense is probably not worth it if you’re potting outdoor plants on a large scale. Economically, garden soil may be fixed for very little money and is best for large garden spaces. Overall, both have their place in the gardener’s world and should be used in the correct application for best results.


Give your plants a balanced diet

Just like people, plants need a range of nutrients to thrive. If you make your own compost, the leftovers from your own balanced diet become food for your garden — but your kitchen compost is limited to the range of what your household commonly eats. Many gardening advisers recommend using at least five different sources of compost: for instance, your kitchen compost plus four different bags from a garden store. In addition, supplementing any known imbalances with targeted amendments leads to great rewards at harvest time.

An all-purpose organic fertilizer is the simplest way to go for the beginning gardener, but armed with the results of your soil test, you may want to fine-tune your beds. Essential nutrients for all plants include:

  • Nitrogen: provided abundantly by leguminous cover crops or composted manure.
  • Phosphorus: rock phosphate and bone meal are both good sources.
  • Potassium: kelp meal or greensand are long-lasting potassium releasers.
  • Calcium: commonly supplied by gypsum or lime. Glacial rock dust provides calcium and other minerals while raising the pH of acidic soil.
  • Magnesium: epsom salts will raise magnesium without affecting pH, while dolomitic lime will raise both pH and magnesium.
  • Sulfur: generally required only in alkaline soil. Adding sulfur will slowly lower pH through microbial action.

Gardening for years with a nutrient deficiency can be so discouraging that it’s hard to stay enthusiastic. Though in the excitement of spring, it may be tempting to rush into planting with whatever dirt you have on hand, take your time. All your labor will be in vain without the appropriate soil foundation. Take steps now to ensure some positive reinforcement for your efforts!


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