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.
- All-Purpose Potting Soil. An all-purpose mix is generally adequate for one season for flowers or vegetables grown in raised beds or containers. A water-soluble fertilizer or slow-release fertilizer added after planting your flowers or vegetables improves flowering and helps produce a good harvest. Read the label for information on any added fertilizers or wetting agents.
- Seed-Starting Mix. Seed-starting mix is a lightweight, quick-draining, sterile potting mix intended to start seeds. It contains additional perlite or vermiculite, so tiny, delicate roots can extend into the mix. It may contain a starter fertilizer.
- Cactus and Succulent Mix. Succulents and cacti, such as Opuntia species, are adapted for environments that range from U.S. Department of Agriculture plant hardiness zones 3 through 10 and require a quick-draining mix. Mixes formulated for cacti contain a combination of ingredients that may include compost or soil, peat moss, perlite and sand.
- Orchid Mix. Epiphytic orchids (Orchidaceae family) require bark, volcanic rock or other loose mix that allows water to drain quickly from containers. Most orchid mixes do not contain fertilizer; apply a water-soluble fertilizer formulated for orchids approximately every other time you water the plant. Grown indoors in much of the United States, epiphytic orchids, such as the Cattleya, Dendrobium and Phalaenopsis species, are hardy in U.S. Department of Agriculture plant hardiness zones 9 through 10, depending on the species.
- A&P Nursery: Garden Soil Vs. Potting Mix | Differences
- Michigan State University Extension: The Shocking Truth About Topsoil
- University of Florida IFAS Extension: Homemade Potting Mix
- The Center for Agriculture, Food and the Environment: Bagged Potting Mixes and Garden Soils for Home Gardeners
- Floridata: Opuntia Humifusa
- Cactus and Succulent Society of Alberta: Grow Cacti Outdoors
- University of Illinois Extension: Composting for the Homeowner: Benefits and Uses
- Soil Nutrient Analysis Laboratory: Packaged Potting Media
- Texas A&M AgriLife: Building a Raised Garden Bed
Ruth de Jauregui is an old-school graphic artist and writer who focuses primarily on garden topics. She writes a weekly garden column and authored 50 Fabulous Tomatoes for Your Garden. She continues to write nonfiction articles on gardening and other topics and is working on a second “50” book about plants that attract hummingbirds.
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 …