How to Fill a Raised Garden Bed

 Raised Garden Bed garden tips

A raised bed garden can be a great solution for properties with poor soil, drainage issues and other problems. Creating and filling raised garden beds can be expensive—especially if you're creating multiple beds at once. However, there are some ways to provide plenty of rich, well-drained soil for vegetables, fruits, flowers, or herbs. This guide will help you decide how to fill a raised garden bed without blowing your budget.

Select and prepare the site

Raised bed structures are usually made of wood, but can be made of bricks, cinder blocks, stones, or galvanized metal. Regardless of the type of bed you choose, you'll need to do some prep work before filling the raised garden bed frame with soil. Choose a level surface for the bed that has the right amount of light for the plants you plan to grow. Most vegetables need full sun to thrive, but some herbs, leafy greens and ornamentals tolerate part to full shade.

After choosing a spot for your garden, use a spade to remove large stones and level the high areas. Place the raised bed frame in its resting place and add newspaper or cardboard to the bottom of the bed to prevent weeds.

How deep should raised beds be?

The recommended depth of a raised bed depends on the types of plants you plan to grow. For example, some perennials, herbs, and leafy greens can grow in beds 6 inches deep, while root crops and larger vegetables (such as tomatoes) generally need beds at least 12 to 18 inches deep to accommodate their roots. Deep beds are expensive because they require more soil, but they filter and retain water better than shallow beds and are more ergonomic.

How Much Soil Do Raised Beds Need?

To find out how much soil you'll need, multiply the length, width, and height of the raised bed structure to calculate the amount of soil in cubic feet. For example, a 1-foot-high 4-by-8-foot garden bed requires about 32 cubic feet of soil (4 x 8 x 1). However, there are ways to fill raised beds with organic matter so you don't have to buy so much soil.

Ways to Fill a Raised Garden Bed

Once your raised bed system is established, it's time to start adding soil. These methods work well depending on the size of the raised bed and the plants you plan to grow.

1. Fill the raised bed with soil

Small and shallow (under 12 inches deep) raised beds are usually filled with soil only. Adding other organic matter to shallow beds is generally not a good idea. Sticks, branches, and other materials further reduce limited soil space and can interfere with plant root growth and water drainage. Smaller beds don't require much soil, so they're less expensive to fill.

Packed bed potting mix is usually used in small raised beds, but you can buy it in bulk from local landscape companies. Another option is to make your own potting mix by mixing equal parts topsoil, compost and sand to create a quality mix suitable for most vegetables, herbs and flowers.

2. Use the lasagna garden method

Large raised beds are expensive to fill with soil alone, so gardeners have found creative ways to fill them with other materials. The lasagna gardening method is usually used to create new underground gardens, but it can also be used to fill a raised bed. To start, lay down sheets of cardboard or newspaper to suppress weeds, then fill the raised bed system halfway with nitrogen-rich materials (such as kitchen scraps and grass clippings) and carbon-rich materials (such as wood chips and dry fall foliage). leaves). Watering the ingredients with your hose as you add them minimizes air pockets and limits the amount of shrinkage that occurs later. After the raised bed is half filled with organic matter, fill the rest of the bed with raised potting mix.

Over time, you may notice a slight lowering of the soil line as the organic matter decomposes, but this can be corrected by adding more soil to the raised bed as needed.

3. Use the Hugelkultur method

Hugelkultur mounds are often used in permaculture gardens and help plants grow better by retaining water and nutrients and increasing soil temperature. However, larger culms can be used to fill a large, raised bed and reduce soil use. To use this method, lay down cardboard or newspaper to suppress weeds, then layer branches and logs at the bottom of your raised bed. As these materials break down, they act as fertilizer for plant roots and help raised beds retain water.

After creating a stack of large logs and branches, stack small twigs, twigs, grass clippings, and autumn leaves around the stacks, pressing these materials into any air pockets you see. Adding water as you go helps the ingredients shrink. If the raised bed is about half filled with these larger materials, fill the rest with at least 6 inches of raised bed potting mix. As with lasagna gardening, it's best to create a large culture bed in the fall to give things time to break down over the winter. You may need to add more soil from time to time as the organic matter decomposes.

Things you shouldn't put in a raised bed garden

Compost, seedless plant debris, kitchen waste, grass clippings, used coffee grounds, newspaper, weed-free straw and other organic materials can be added to raised beds to fill space and reduce soil use. However, some items should not be included in raised beds, including:

Garden soil may seem like an obvious choice for filling raised beds, but garden soil doesn't usually work well. The soil from your garden will be denser, and it will become more compact in the raised bed. Over time, this dense soil can affect water flow and inhibit root growth. Plastic sheets are sometimes added to the bottom of raised beds to keep out weeds, but as the plastic ages, it becomes brittle and disintegrates into messy pieces of plastic that get stuck around plant roots. Cardboard and newspaper are good choices for weed control at the bottom of raised beds because they will naturally break down and become soil.

Rocks or gravel are sometimes added to raised beds to increase drainage, but this practice can create a false water table and affect water flow. The best options are to grade the soil around your raised bed from your garden and make sure it has good drainage. Treated lumber is not a good option for filling garden beds. Most woods can be added to the bottom of raised beds to fill the space, but make sure those trees are not treated or painted.

Plant materials from allelopathic and water-resistant plants should not be used. Black walnut suppresses the growth of nearby plants, and cedar is naturally water-resistant. If you're looking for material to add to the base of a large raised bed, it's best to avoid branches, twigs, and logs from these trees.