Raised beds are becoming more popular, but do they make sense for the garden? What benefits do they provide? Will they grow more food than convention low beds? Does a raised bed need to have side walls? What is the best building material and soil for raised beds? In this and the following posts I will try to answer all of these questions so that you can make an informed decision about adding raised beds to your garden.
What is a Raised Bed?
The term raised bed is a bit confusing. If you add a few inches of soil to a garden bed that is at ground level, it is a raised bed. When most people talk about raised beds for vegetable growing, they mean a bed that has been raised with walls surrounding the soil, sometimes called a garden box or framed bed.
I’ll use the term raised bed to mean a bed that has walls and compare it with a traditional bed that does not. A traditional bed may or may not be raised above grade, but it is usually not raised more than six inches.
Benefits of Raised Beds
The pro side make many claims for using raised beds. The problem with many of the claims is that they are not comparing apples to apples. When you compare raised beds, using intensive cultivation to traditional farming practices you do find many benefits, but that comparison makes little sense. If you want to understand the real value of raised beds you need to compare them to intensive gardening done on level ground, or even raise ground without side walls.
I will look at many of these myths in a future article on GardenMyths.com, but for now here is a summary of some claims for raised beds that are not true.
- need fewer seeds
- has fewer weeds
- more productive
- longer growing season
- less compaction
Raised Beds – the Pro Side
There are some legitimate reasons for using raised beds.
- The garden looks neater. The walls keep soil in place, and pathways can be kept cleaner.
- They require less bending to work on the plants, but a 12 inch wall does not help much for us tall folk.
- They can be used in areas that have very poor soil, contaminated soil or no soil at all. Containers are small raised beds.
- They warm up quicker in spring, allowing earlier planting.
- They can be great for people with a disability.
- Different beds can hold different types of soil allowing you to match soil to crops.
- Drainage can be better in areas with very poor drainage, but raised beds can also cause drainage problems.
- Bottoms can be screened to keep gophers and voles out.
- Helps keep kids and pets from stepping onto plants.
Some people claim they deter slugs and animals like rabbits. Others say they have no effect on these pests.
Raised beds may help concentrate resources like compost and fertilizer to the growing areas, but if you are careful you can also do this in a non-raised bed.
Notice that none of these reasons have anything to do with higher productivity, better flavor or improved nutrition. If you grow the same food, in the same kind of soil, raising the soil level and adding walls will produce exactly the same food as growing in the ground.
If you use better soil in a raised bed then it might produce more food, but you can also use better soil on the ground.
Techniques like square foot gardening make all kinds of claims for improved productivity, but the reason for increased productivity is due to intensive cropping – not the raised bed. You can do all of the intensive cropping on level ground.
Raised Beds – the Con Side
There are some very good reasons for not using raised beds.
- You have to buy soil, unless you have high spots in your yard that you want lower.
- They cost money to build.
- Soil dries out much faster in summer.
- Requires more watering.
- Less sustainable since you need to buy and transport walls and soil.
- There is some concern about chemicals leaching from the material used to build the walls.
- Soil gets warmer, which is not good for roots, except in early spring.
- Perennials need to be hardier since a raised bed gets colder in winter.
- The rows between beds need to be wider if you plan to use a wheelbarrow with taller walls.
- Drip irrigation is more difficult to install.
- Soil cools down quicker in fall.
Productivity is probably better without a raised bed. The roots of a tomato plant in the ground grow several feet in all directions, but in a raised bed its root system is confined. Raised beds dry out quicker in summer, and water becomes a limiting factor for yield. Given good soil, and the same amount of fertilizer and water, it is hard to see how plants crammed into a raised bed would produce as much food as in the ground.
Are Raised Beds Better?
Unless one of the pro arguments is very compelling for you, I recommend gardening on the flat ground. This is especially true if you are a first time gardener or someone that might move in a few years. Give it a try before spending the extra time and money building walls.
Read all about intensive cropping, including such topics as wide beds and succession planting. If drainage is a problem, you can move the soil from the paths onto the growing beds to raise them a bit. Adding organic matter will raise them a bit more. With beds that are eight inches taller (no walls) you will have a very productive garden, and the obvious paths will keep you from walking in the growing areas (unlike the lady in this picture).
I don’t normally recommend books, but these are very good for learning more about intensive vegetable gardening.
- Photo source 1 and 2: under license
- Photo source for Vegetables in wide beds; Kate Holt/AusAID