Before beginning to build a raised garden, it is important to determine why a raised garden is needed or desired. Included in this assessment should be a consideration of the type of plants to be grown in the garden. Raised gardens are used to make a garden more convenient, to offer better soil content, for ornamental purposes, and a few other good reasons.
A raised vegetable garden may not be best for a landscape feature.
If the garden is being raised as a landscape feature, it may not be the best idea to make it a vegetable or herb garden because most of these plants are not perennials. This will mean that the garden is vacant and a possible eyesore for half of the year. Raised landscape gardens are best filled with small evergreen shrubs that can be surrounded by other perennials or annuals when the time is right.
Convenience and soil improvement are two excellent reasons for a raised garden.
Elevating the soil bed a foot or two can make weeding and pest control much easier. Having a raised garden filled with high quality soil for the plants will also mean less plant feeding and better sustained growth and crop production. It also affords more ability to see what the plants are doing regarding growth and health.
Regardless of the purpose, you can make the raised garden attractive if it is visible to the neighborhood.
While almost any material can be used to make the framework for a raised garden, some choices will make a more pleasing look. All types of landscaping material choices should be attractive and durable if installed correctly. For raised gardens that are intended for function only, using old railroad ties or recycling treated lumber will work fine. Some people have even used old truck tires although you might want to investigate the environmental impact as these degrade.
Pick a spot that will not need a lot of reshaping to make construction easier.
Unless you are in the middle of a major landscaping operation at your house, the best place for a raised garden should not need major excavation before construction begins. It is a good idea to remove any grass and plants that are already present in the site. However, if you intend to put a barrier under your raised garden, this may be unnecessary.
Determine the volume of your garden ahead of time.
Stake out the spot and compute the number of cubic feet of soil that you will need to fill your garden. This will help you decide whether to buy bags of soil or have it brought in by truck. It is usually much cheaper to have it delivered by truck if you need a lot. It is a good idea to buy a little extra soil to compensate for any unlevelled areas. If you have determined the height of the walls of your raised garden, just multiply the length times the width times the height in feet to get cubic feet. While you are at it, find the perimeter of your plot so that you can buy enough materials to build the walls.
For extra tall walls, buy lumber to use as anchors.
Most raised gardens are only about 12 to 18 inches tall. At this height, little, if any, engineering is necessary. If the wall grows to 3 or 4 feet or taller, you will find it needs to be anchored with boards passing through the wall and reaching several feet back into the garden plot. These will act as secondary foundations for the upper part of the wall and keep the built up soil from pushing the wall over. Just fit one in every couple of feet and attach the wall to it if you are using wood for the wall. Some of the manmade materials interlock and do not need this extra support.
Install a footing if you want to keep moles and other similar pests out.
A shallow footing of 12 to 18 inches deep will stop most moles from entering your garden. Just dig a simple trench and fill it with concrete. You can reinforce it if you will be building a heavy wall. Otherwise, putting metal into it is not really required. This shallow footing can be helpful if you make it a little wider than needed so that grass growth is kept away from the wall. It will make mowing around your garden much simpler.
Build your wall to the desired height.
For wood or other materials that you intend to install straight up and down, just build up your wall until it is the correct height for your raised garden. Some types of stone may be best installed by laying a row and filling with dirt. Let the next row rest with the inside edge slightly on the dirt. Repeat this process until the wall is complete. The finished wall should have a slightly sloped appearance. Do not let the slope be too great or the settling dirt will allow your wall to collapse.
Lay a barrier over the bottom of the garden.
For most raised gardens, it is a good plan to lay a barrier like paper or plastic over the exposed earth before filling the garden. This will help the garden retain more of the moisture that come into it. Some gardeners prefer no barrier so that roots can penetrate deeper into the earth. However, if the soil of the plot is the problem, this approach can be counterproductive to the garden.
The garden should be ready for planting.
With the good soil and raised garden, it is time to get some great plants and start your gardening. If you have used regular topsoil for your garden, you may want to get some type of water soluble plant food to begin feeding your new garden right away. Make sure that you use plants suited for the amount of sunlight available to your garden.