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How to Mix Soil for Raised Beds

An advantage of gardening in raised beds is that you can control exactly what soil you use to grow your plants. Raised beds are growing areas that are higher than the surrounding ground, and they're often surrounded with low walls to prevent the soil from spilling out. The soil in raised beds should be organically rich and freely draining to provide the best growing conditions for plants, and you can create this effect with a mixture of topsoil, organic material and sand or perlite.

Soil Ingredients

Topsoil provides stability in raised beds; organic material adds nutrients and improves the water-holding capacity; and sand or perlite provides drainage. Topsoil is the top layer of ordinary soil. If the soil in your garden is free of diseases and contains few weed seeds, you can use this in raised beds. Otherwise, you can buy topsoil from your local garden supply store.

Aged manure, garden compost, fine bark mulch, mushroom compost and peat moss are some examples of organic material you can use in raised beds. Organic material helps prevent raised beds from drying out quickly by holding onto water without becoming soggy. Some kinds of organic material, such as aged manure and rich garden compost, also contain slow-release plant nutrients.

Many plants grow best in soil that contains air pockets, which allow their roots to breathe. Sand and perlite encourage excess water to drain away quickly, preventing air pockets from becoming saturated with water.

Mixing Method

Push a garden fork into the soil at the base of the raised beds and lever it upward to loosen the soil all over the base. A rough surface at the base of raised beds encourages water to drain into the soil beneath.

Mix 2 parts topsoil, 1 part organic material and 1 part sand or perlite with a garden spade, and fill the raised beds with the mixture.

Rake the soil surface until it's level. Wait a week or longer before planting in the beds to allow time for the soil to settle.

  • Many plants grow best in soil that contains air pockets, which allow their roots to breathe.
  • Push a garden fork into the soil at the base of the raised beds and lever it upward to loosen the soil all over the base.

Quick Method

A quick method for creating raised beds is to mix the existing garden soil with organic material.

Spread a 4- to 6-inch layer of garden compost, peat moss or aged manure over the soil surface, and mix it into the underlying soil with a garden fork. Shape the edges of the bed to a 45-degree angle and firm them with the back of a spade.

If the raised bed edges begin to slip over the growing season, rake them back into place. Spread a 2-inch layer of organic mulch over the soil surface after planting or harvest every year. Mulching after planting helps conserve soil moisture and control weeds, and mulching after harvest helps prevent winter rains from washing nutrients from the soil.

Optimal Soil-to-compost Ratio For Raised Beds

Installing raised beds is one way to avoid digging in heavy clay, rocky or sandy soil. While building a raised bed is relatively easy, you still have to fill it with soil and compost. The classic soil-based mix for a raised bed incorporates equal parts garden soil, compost and sharp sand. When garden soil isn't available, mixing equal amounts of bagged topsoil and compost will get your garden started with a minimum of effort. To fill a 4-by-8-foot, 10-inch-tall raised bed, you need 1 cubic yard of soil mix. A cubic yard equals 27 cubic feet.

  • A quick method for creating raised beds is to mix the existing garden soil with organic material.
  • Spread a 4- to 6-inch layer of garden compost, peat moss or aged manure over the soil surface, and mix it into the underlying soil with a garden fork.

Tip

To fill a raised bed measuring 4 feet by 8 feet by 1/2 foot, you need 16 cubic feet of ingredients, or 8 cubic feet of topsoil, 4 cubic feet of organic material and 4 cubic feet of sand or perlite.

Warning

Don't stand on raised bed soil. Foot traffic compacts the soil and makes it difficult for plant roots to penetrate.

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