Raised beds have become very popular amongst gardeners. There are advantages and disadvantages to using raised beds however, so it’s a good idea to think about why you need them and how you will build them before you start, to make sure that they are the right choice for your garden.
Advantages of Using Raised Beds
Raised beds enable you to grow almost anywhere. It doesn’t matter what your existing soil is like, or even if you have soil underneath them. With a raised bed you can add your own soil and compost, which gives a great weed-free start to your garden.
Walking on soil squashes it down, removing the essential air pockets in the soil structure, which can make it difficult for plant roots to grow through and prevents the free drainage of water. This can be especially problematic on heavy clay, but all soils do much better if beds and paths are clearly separated. Building raised beds is an easy way to do this as it provides a clear physical divide between the growing area and the paths between them. It’s also a good way to encourage young children to join in with the gardening without stepping on precious plants.
Raised beds should always be narrow enough to enable you to reach into the middle for weeding and harvesting without stepping onto the soil. 4 feet (1.2 metres) is usually the maximum width. If you are building them against a fence or wall, you’ll probably want to limit the width to 2 or 3 feet (60-90cm) since you can only access them from one side. It’s usually sufficient to build them 6 inches (15cm) high, although up to 12 inches (30cm) is used for root crops.
By filling raised beds with a rich mixture of potting soil and compost, plants can get the nutrients and moisture they require at closer spacing than traditional row-based planting. With fewer gaps between plants, there’ll be less room for weeds too, which reduces the amount of time you have to spend maintaining them.
Disadvantages of Using Raised Beds
This all sounds great, but there are some disadvantages to raised beds too. Because you need to construct them from wood or other materials and then fill them with compost and potting soil, they’re more expensive to begin with than a traditional vegetable garden.
Another issue, particularly if you live in a dry climate, is that due to the increased drainage they often need more watering during hot weather than ground-level plants, so you may need to install a permanent irrigation system to make this easier.
Building Raised Beds
The next decision is whether to buy a raised bed kit, or build it yourself. Raised bed kits have the advantage of being easy to construct and the wood is often pre-treated to prevent rotting. You can also buy recycled plastic beds or boxes on stilts which require less bending or enable wheelchair access.
If you decide to build the beds yourself, it’s important to remember that wood rots. To ensure that the wood lasts for as long as possible, there are a few options:
- Use treated wood. Pressure-treated wood has a mixture of chemicals applied to prevent the moist soil and weather rotting it. Many people have reservations about using it however, and there are various eco-alternatives available to treat wood which are derived from natural products.
- Use cedar or larch. Hardwood is usually longer-lived than softwood, but cedar and larch contain natural oils which prevent rotting and make them much more durable. They are more expensive to buy but they will last for many more years before they need replacing.
- Choose thicker boards which will take longer to rot. For example, 2 inch thick larch should last for at least 10 years, even without treatment.
Once the beds are built, it’s time to fill them with soil. To gain the maximum benefit from raised beds the soil needs to be a rich mixture of soil and composts from different sources. With a good nutrient-rich mix, you usually won’t need to add fertiliser – an inch of compost spread on top each year will keep nutrient levels high.
In our Garden Planner you can either draw out raised beds using the Rectangle tool, or you can pick one of the Raised Bed icons from the selection of Garden Objects to give a realistic look to your plans. It’s easy to resize each bed to the dimensions you have chosen and you can copy and paste beds as required. Don’t forget to leave adequate space for paths – at least 2 feet wide is required for comfortable kneeling down to access the plants. You can quickly add plants to your beds and the Garden Planner will show how many will fit in each, at the right spacing for optimal growth. Drip irrigation can also be added if required.
For more intensive growing, consider the Square Foot Gardening method which combines raised beds with a special soil mix and different plants in each square foot. See our article and video on Growing Vegetables with Square Foot Gardening for more details on how the Garden Planner can help with this.
Raised beds are low maintenance and can yield big harvests for the space they occupy. A good idea is to start small and then add extra beds as your time and budget allows - that way you’ll gradually build up to a highly productive garden that should set you up for success over many years.