Raised Deep Bed Gardening

About Raised Beds

In recent years the popularity of deep bed growing for fruits and vegetables has increased but I've noticed many people decide to start growing this way without an understanding of the benefits and drawbacks as well as a lack of understanding of how to construct a deep growing bed.

History of Raised Beds for Vegetables

Before looking at the pros and cons of deep beds, it's worth looking a little bit into the history of modern deep bed growing.

The idea became popular in the early 1970s where the construction was to dig over a bed to deep and fine tilth which was mounded between paths. Because the bed was a rounded shape there was more surface area to grow on and this, coupled with higher density planting increased yield. (see diagram)

Unfortunately heavy rain would wash the bed onto the paths and defeated the object of the exercise.

Converts to deep bed growing soon moved onto walled sides to their deep bed, losing the benefit of the additional area, which was not much but gaining the stability of walled construction.

Is Raised Bed Growing for You?

Before constructing deep beds you should really consider if they are the right thing for you. Weigh the advantages and disadvantages carefully before going into construction.

Advantages and Disadvantages of Raised Bed Growing

Constructing deep beds correctly is hard work and can be quite costly in terms of materials but once done they are easy to maintain and should last for many years.

Yield per square foot is higher with a deep bed but the space taken up by paths means that it is generally equal to ordinary growing methods.

Because of the closer planting with deep beds weeds are suppressed but they still require weeding and this is usually done by hand, which takes longer than hoeing a conventional row. Psychologically deep beds are easier to keep in order as you can select and clear a bed at a time rather than coping with a whole plot.

Not all vegetables are ideal for deep beds and for some vegetables you will probably need to select varieties that are suitable for close spacing just as for container growing.

Deep beds can be ideal for purpose made large cloches and fleece supports.

Raised beds generally enable you to create high quality areas of deep topsoil if your soil is poor but are a lot of effort if you have a good quality soil to start with.

Deep beds can be very attractive and enhance a garden situation where a normal vegetable plot would look out of place.

Raised beds are, once the hard work of construction is done, easier to maintain and enable those less physically able to continue growing when they are not up to digging over large plots.

Decorative Raised Beds in a Garden

Before I go on to constructing a raised bed, in a garden situation you can make raised beds a very attractive feature. Instead of laying out in the most efficient method you can make them into architectural features, altering the height of some beds to provide focal points.

One idea I liked was to construct the beds utilising old scaffold boards stacked two and three high but then covered with woven willow panels (hurdles). These were raised above the bed edge providing a sheltered micro-climate inside the beds as well as an attractive addition to a formal garden

How to Construct Raised Deep Beds

Size of Raised Deep Bed and Paths

The main point of deep beds is that you never tread on them and compact the soil so it is important that you can easily reach into the centre from the side of the bed. The best width will be around 1.2M (4 feet) to allow that.

If the bed is too long, then getting to the other side will involve a long walk and you will be tempted to step over the bed so about 3M (10 feet) long is considered maximum length..

The main paths will need to be between 60cm (2 feet) and 75cm (2'6") to allow easy access with a wheel barrow with the secondary paths around 45cm (18") wide to allow walking and kneeling as you lean over the bed.

Constructing the Raised Bed

First plan out where the beds are going and use some line to mark out. Don't be tempted to squeeze the paths, you will regret it. Better to have a narrow bed because you will not be able to get to the bed with too narrow a path.

Having marked out and checked you are happy with the layout you can produce a cutting list for the wood for the sides. One good source can be second hand scaffolding planks if they are in reasonable condition. Do not use wood that is too thin, like floorboards, because it will rot and be too flimsy.

225mm x 38mm (8.8" x 1.5" approx) boards are near perfect. Fix to stout internal corner posts, fence posts can be ideal, with non-rusting screws. Because the wood is in touch with the ground it will be prone to rot so paint with a preservative like Cuprinol, soak the corner posts, for a long life. The corner posts can be sunk a few inches into the ground to improve stability.

One good idea is to have a finial decorative ball fixed on the top of the corners, like they use for the main posts on stairs. Not only do they look really well but they help when you pull a hosepipe through to a bed, stopping it from dragging across the plants.

Now, and this is important, before you put the wooden frame into position you need to double dig the bed removing and perennial weed roots and incorporating lots of organic matter like compost or manure into the base of the trench. Break the soil up well as you do this.

Now position an level the base using a spirit level. Allow the soil to settle for a few days and then incorporate compost into the top bringing the soil level up to about an inch or 25mm below the top of the boards.

Your raised deep bed is now ready to plant.

Paths Between the Raised Beds.

Once the beds are in place it is time to complete the paths between them. Level them out and compact them if loose. A shuffle walk up and down can do this. The easiest thing to do is to buy some porous weed suppressant fabric material. Cut to size and lay over the paths and then cover with bark or wood chippings.

I have seen paths made from concrete slaps, if you use these check the sizing accurately when you position the beds and save yourself a lot of work later.

Other materials you can use are gravel and even block paving bricks.

My Own Feelings on Raised Beds on an Allotment.

Growing as I do on heavy clay, I think raised beds offer a great way to grow but the expense in both time and money is considerable. Also I don't think they are ideal for crops like potatoes, Jerusalem artichokes and sweetcorn. Neither do I think they offer any significant advantage for growing broad or runner beans. They are brilliant for root crops like carrots and parsnips because they offer deep fine soil. They also work well for a salad bed, turnips and beetroot.

I wouldn't turn an entire allotment over to raised beds but I certainly would have some on the plot.

The plan below shows deep beds with primary and secondary paths