Topsoil vs. potting soil
Using the right kind of soil is the key to successful gardening. (Photo: GoodSeed Nursery photo )
What is the difference between topsoil and potting soil and which one should you use? That depends on what you’re using it for.
First, let’s understand what we mean by the words topsoil and potting soil.
Topsoil is dirt, and potting soil isn’t. True potting soil is actually “soil-less.” Topsoil is for planting in the ground. Potting soil is for planting in containers. Topsoil is sand or clay (ground-up rocks) mixed with organic materials such as compost. Potting soil is a mixture of peat moss and other organic materials such as composted sawdust.
Topsoil is heavy. Potting soil is mostly air so it’s light. Topsoil holds lots of water, so it will stay moist for a long time. Potting soil lets water drain easily, so it dries out quickly. Topsoil is dense and packs down easily. Potting soil is fluffy and hard to pack down.
The word topsoil can mean many different things because no two topsoils are exactly the same. Topsoil means the very top layer of the Earth’s crust, rich in nutrients because plants have lived and died in it, sometimes for thousands of years.
The topsoil you find in woods contains lots of rotted vegetation. Topsoil in farm fields has been turned over, mixed and often exhausted by repeated plantings. Topsoils often contain clay or composted manure. They also contain weed seeds, soil bacteria and fungi.
Potting soils are precisely mixed using strict formulas and recipes. Most potting soils are based on peat moss, with other ingredients added to make them ideal for certain uses. For example, seed starter mixes are very fine and fluffy so that fragile, fine roots can spread easily. Perennial mixes have larger pieces and more bark.
Some potting soils include vermiculite or perlite; flakes of fluffy featherweight rock that’s been puffed up so it holds lots of air. Good potting soils are sterile, meaning they have absolutely no weed seeds or diseases in them.
Topsoil is ideal for filling in low spots in lawns or along walks and patios. Adding a few inches of topsoil gives lawn grass a better chance than subsoil or clay. When planting trees and shrubs, replacing the existing soil with topsoil can help plants grow better.
We sell “pulverized” topsoil, which is perfect for fine-grading because it doesn’t have lumps or clay in it. As long as it’s dry, pulverized topsoil is a breeze to spread and rake.
For raised beds, topsoil is much cheaper, as it’s sold in bulk, but it should be mixed with compost, peat moss or vermiculite to make it fluffy and improve drainage. Otherwise, it will pack down, swell and break your raised beds.
Depending on what you’re growing, we can blend ingredients in the right proportions.
Potting soils are for planters, hanging baskets, window boxes and other containers where drainage is important and weight would be a problem. Potting soils allow excess water to quickly drain out the bottom of the container by gravity, pulling in air to replace the water.
Because plants breathe through their roots, they’ll thrive in potting soil as long as they are watered regularly. Some potting soils have moisture crystals, bits of polymer that help keep them from drying out so quickly.
Using the right kind of soil for the project you’re doing is one key to successful gardening. If you’re not sure, just ask.
Steve Boehme and his wife Marjorie own GoodSeed Nursery & Landscape, near Winchester.
What is the difference between topsoil and potting soil and which one should you use? That depends on what you’re usi…
Should I Buy Topsoil or Potting Soil for My Flower & Vegetable Garden?
Topsoil and potting soil have specific uses and are not interchangeable. While topsoil is available in large amounts and is relatively inexpensive, potting soil is formulated for general or specific plants’ needs. Whether you select topsoil or potting soil depends on the volume needed, your budget and the types of plants, flowers or vegetables that you intend to plant.
Topsoil is simply the top layer of soil scraped from the ground. It may be rich river silt, or it may be mostly sand or clay and, in any case, will have weed seeds mixed in. When you purchase topsoil, you don’t know what you’re getting unless you personally select it from the choices at the landscaper’s supply yard. A soil test will identify the nutrients and micronutrients that should be added to make it suitable for a garden or container.
While topsoils vary according to your supplier’s sources, they provide a base for your garden, raised beds or containers. To improve the topsoil, add compost and well-decomposed manure and mix it together before adding it as a topper for fill or poor soils. Do not add gravel or sand to clay soils; clay, sand and gravel will harden soil into a concrete-like mass when it dries in the sun.
- Soil Topper. In new subdivisions where the original topsoil was scraped away by the contractor or locations with rocky or extremely poor soil, topsoil covers the compacted soil and provides an environment where landscape plants can root. For best results, till the top few inches of the existing fill or soil, rake 2 to 3 inches of topsoil over the garden and then till again. Mixing some topsoil with the fill provides a transitional mix that helps the plants’ roots penetrate into the fill or poor soil below the added topsoil. Add the remainder of the topsoil to the garden. When adding topsoil, slope it away from the house or outbuildings to ensure that stormwater drains away from your crawl space or basement.
- Raised Gardens. When building raised gardens, mix topsoil with compost and peat moss or coconut coir to make a general mix for gardening. Depending on the quality of the topsoil, the mix might be 3 parts topsoil to 1 part compost or equal parts topsoil and compost. A mix for a vegetable garden might also incorporate sand, in a combination of equal parts topsoil, peat moss or coconut coir, and sand. If the topsoil is acidic, put on gloves, goggles and a dust mask and mix in lime according to a soil test. If the topsoil is alkaline, add sulfur and peat moss to increase its acidity. If the topsoil is filled with clay or sand, add additional compost, coir or 1/4-inch bark to increase the ability of the mix to drain or retain water.
- Container Gardens. While potting soil is often used in container gardens, topsoil may be used in soil-based mixes. A basic soil-based mix incorporates equal parts topsoil, compost and perlite, vermiculite or sand. Although heavier than commercial potting soils based on peat moss, this mix provides good drainage for potted trees, shrubs and other plants.
Potting Soil Basics
Potting soils are quick-draining mixes suitable for container gardening. They generally contain a combination of compost, peat moss and perlite. The ingredients vary according to the manufacturer and intended use of the mix. Some mixes also contain fertilizers and wetting agents that may or may not be suitable for your plants. Always read the directions on the package to ensure you purchase the correct mix for your plants.
Should I Buy Topsoil or Potting Soil for My Flower & Vegetable Garden?. Planting mixes such as potting soil and topsoil are formulated to help plants thrive in different growing situations. When preparing an outdoor vegetable garden or flowerbed, knowing the differences between topsoil and potting soil ensures you …