Raised Bed Planting & Growing Guide | Horticulture.co.uk (2024)

By KERSASP SHEKHDAR

Long used on allotments for growing vegetables, raised beds have enjoyed a steady uptick in popularity, and for good reason.

They offer a controlled, self-contained growing environment and allow easier gardening with less strain.

They are also fairly easy to build as a DIY project.

Also, if a raised bed is made with the right materials it will last for well over a decade.

What Is A Raised Garden Bed?

A raised garden bed is a rectangular bed that is elevated to a fair degree from the ground and is enclosed on all four sides with short walls.

Typically these rise to upper-shin height.

Types Of Beds

Garden beds are usually one of four types:

In-Ground Or Soil-Level Beds

Mounded Beds

Raised Beds

Container Beds

A mounded bed is one in which soil is formed and shaped into an oblong mound.

As the mounded soil has no supports the soil gradually slides down to ground level.

Such a bed sometimes does not survive a heavy downpour.

A container bed is one which is not only enclosed on all four sides but also has a base or a floor.

“Container-raised beds are difficult to grow in now the climate is so erratic because we are getting very dry springs and summers,” explains Val Bourne, an expert Gardener.

“Raised beds really do dry out, but they are also wet in the winter with nowhere for the water to go because they have wooden sides.

“I much prefer to use small in-ground beds with planks in between that you can walk on now, which I’m finding is an improvement. I’ve turned my existing container beds into flower beds.”

Benefits Of Raised Beds

“We broke our allotment plot down into bite-sized chunks and made lots of raised beds, using reclaimed tiles, fence panels and wooden pallets, and created pathways in between each bed,” shares Garden Blogger Joe Harrison.

“By doing this we were able to manage the site a lot easier and the paths meant that we weren’t walking on the soil and compacting or damaging it.

“Raised beds are a great way to utilise space and work well for those who have very poor growing conditions, as you can fill the beds with nutrient-rich compost and provide the perfect growing environment for almost any fruit or vegetable.”

Raised beds offer other various benefits, which include:

• A self-contained gardening environment.
• Controlled soil or even a specific soil mix as distinct from that which is on the ground.
• Ability to bypass ground soil that may be poor or contaminated.
• Drainage is automatically enhanced.
• Plants are relatively closer to eye level, resulting in better observation and easy access.
• No chance of accidentally stepping onto the bed.
• No bending down or squatting means less strain and an easier gardening setup.
• Easier to work on after a rainy spell than a ground-level bed.
• Earlier start to the season because raised beds’ soil warms up quicker and earlier than ground soil.

Crops To Grow

“You can grow almost anything in raised beds, (depending on their size) including soft fruit bushes, vegetables, perennial & annual flowers, shrubs and alpines,” shares Gardener Hannah Reid.

“I grow a range of plants in my raised beds – some of my beds even have fruit trees planted in.

“I enjoy companion planting in my raised beds too, such as growing squash with dill and nasturtiums and marigold with beans.”

First, any and all types of herbaceous and most shrubby plants can be grown in a raised bed.

These include evergreens, ornamentals, vegetables, edible herbs, and smaller fruiting plants such as strawberries and blackberries, as Joe explains:

“There really are no limits to what can be grown in a raised bed. We have grown every vegetable thinkable in ours with no issues whatsoever.

“The only consideration you perhaps need is the amount of space your mature plants need. This will avoid overcrowding and will ensure a more successful yield when it’s time to harvest your produce.”

Raised beds are particularly helpful when your garden has packed or heavy soil and the plants you wish to grow require very good drainage.

I personally believe that the best crops to grow in raised beds are almost all kinds of vegetables and herbs excluding those that grow on tallish climbing vines.

To grow root vegetables in a raised bed it should have a depth of at least 60cm.

I suggest that you try growing leafy greens, carrots, turnips, leeks, beetroot, courgettes, chillies, and tomatoes in your raised bed.

How To Build A Raised Bed

“Raised beds don’t have to be expensive – using reclaimed materials as we did works perfectly,” shares Joe.

If you intend to build more than one raised bed, first survey the available ground and measure the surface area.

Visualise the raised beds that you would like to make, then sketch out a plan for your raised bed.

It’s important to consider the length and width, the spacing between them (if you’re making multiple beds), and the height.

Finally, using a stick, etch out the boundaries of the raised beds on the ground, or mark them out with twine.

First, clear the area of the planned raised bed, making sure to remove any weeds or stones, etc.

Then level and firm up the ground.

You may even remove some of the ground soil and fill it with your preferred soil – though this is an optional step.

Smooth down and make level the ground specifically along the borders where the walls’ timbers will be laid.

To build a raised bed from timbers you will need four regulation 3x3inch posts of the appropriate height, an even number of appropriately-sized timbers for the long sides, and the same number of appropriately-sized timbers for the ends.

The number of timbers you need on each side and each end depends on how high you will make your raised bed and on the width of the timbers.

If the length of the raised bed will be 12m or more, you will need battens of the appropriate size or 2-4 additional posts.

This is because such a long raised bed will need one or more battens or posts along its length for additional support.

“I would advise you to think about the sizing of your raised beds,” says Garden Blogger Emma Bailey.

“You should be able to reach the middle of the bed from the side so that you can easily harvest and weed them without stepping onto the soil. Also, be warned that wooden sides will attract slugs and snails! They love to sit along the side of my wooden sides, especially when it’s been raining.

“I”’ve started leaving out a couple of planks of wood along the pathways to attract them. Then I can remove them easily before they have a chance to move into one of my raised beds. Keep your enemies close!”

The timbers should have holes drilled in at the ends for screws and the posts should have pilot holes.

The holes in the timbers and pilot holes in the posts should be drilled according to measurements and must line up.

Draw a line around each post so as to mark the depth that it will be sunk into the ground, which should be 20cm as a minimum.

Drive in each post at a corner of what is to be the raised bed, and shore it up.

First, put one of the shorter timbers at one end.

If the walls will be made of more than one timber, as is most likely, start from the bottom.

Screw it in fully on the outside of the post, then do the same for the other end.

After fastening one timber on each end, screw in one timber on each side, doing the lowest one first.

Then, if the walls are to be made of more than one timber, go back to the ends and work your way up.

“I love growing in raised beds and set them all up in the same way as I’d set up a growing space directly into the ground,” shares Allotmenteer Shannon Keary.

“I lay good thick cardboard down, ensuring no staples or sellotape are on them, then half fill the raised bed with a composted wood chip which is plentiful on our allotments and top it off with compost.

“This helps with moisture retention, to suppress the weeds and to let nature do its thing. Each year I top if off with an inch or so of fresh, homemade compost so it’s really low maintenance.”

Width

Though the maximum length of a raised bed depends on the surface area at your disposal and good design practice, the width is a function of something highly individual and variable: your reach.

I feel that the width of a raised bed should be tailored for the person or persons who will grow plants in it.

This ‘tailoring’ is quite easy to do.

Assuming that you can stand on either side of the raised bed, you need to be able to reach to about the middle of the bed.

You may need to reach to the middle to harvest veggies or prop up a plant that has flopped over, and you would certainly like to garden comfortably and confidently.

Though you will be leaning forward, most people garden with their arms downwards and not fully outstretched.

As such, the width of the raised bed should not be twice the length of your arm.

I’d suggest that a width that is 170-180% of the length of your arm will be ideal.

If you inherit a raised bed or make one out of prefabricated materials and cannot reach to the middle of your raised bed from the sides, that is not a major problem.

You can instead grow vegetables in rows, leaving the middle of the bed as a walkway if you need it.

“The old-school approach, particularly to vegetable gardening, has this obsession with spacing and how far apart plants should be from each other,” shares Kate Cotterill, Garden Designer.

“Personally, I ignore this. In my raised beds, I interplant, so I’ve got something growing vertically, something horizontally.

“I pretty much ignore all the rules about spacing because as long as you’ve got good compost, then actually there’s enough nutrition for all of the plants.”

Depth

The depth of your raised bed is basically a function of three variables:

• If you are placing a raised bed on ground that is cemented over.
• How much and how well you are able to bend, stoop, and crouch.
• What exactly you intend to grow in the raised bed.

Building a raised bed on ground that has been cemented over will pose a special type of challenge because of drainage.

“In this case, you could fill the base with stones or rubble, as long as there is not much mortar on it, and drill some drainage holes in the sides at the base,” says Peter.

The poorer or more unworkable the soil, the less well you can bend, stoop, and crouch, or the deeper-rooting plants you plan to grow, the deeper your raised bed must be.

If you plan on growing bulb plants, strawberries, tomatoes and such, a depth of only 30cm is quite enough.

On the other hand, if you intend to grow large root vegetables or deep-rooting plants, a depth of at least 60cm is called for.

As a general rule, a depth of 45cm is a good plan.

This depth is sufficient for most ornamentals and also many vegetables.

“I’ve known large raised beds lose more than 20cm of their depth in a single season as the soil’s structure and air pockets gradually collapse,” shares Peter.

“Mixing mineral material, such as soil or loam, with organic material, perhaps garden compost, helps to overcome this, as will consolidating the soil for every few centimetres added.

“Don’t squash all the air out of it, but rake level and firmly tamp down with the back of a rake across the surface.

“Doing this several times during the filling process, and again at the end, works well.”

Commonly-Used Materials

“Setting up raised beds can sometimes be expensive, depending on how you decide to go about it,” says Hannah.

“Sourcing wood and materials to make the beds and then compost to fill them can be costly.

The most commonly-used materials are timbers, often pressure-treated timbers.

Pressure-treated wood lasts much longer than untreated wood, especially when it is used to build a raised bed as the wood is in constant contact with water and damp soil.

“Old decking boards etc are a good option, however, it is important to bear in mind the longevity of the wood and how long they’re likely to last.

“A great tip is to use wood at the bottom of the beds, this will take up space in the beds meaning less compost is needed, but also the wood will decompose over time.”

Cedar, redwood, oak, and pine are very commonly used types of wood.

Other materials include concrete, stone, bricks, paving slabs, railway sleepers, and sheet metal.

Pre-fabricated or readymade raised beds are also available.

These are usually made of timbers, metal, fabric, or synthetic material like High-Density Polyethylene (HDPE).

However, they do need to be assembled.

If you plan on building a raised bed with wood, we suggest that you shop for MCQ-treated timbers.

Raised beds made from concrete or stone will last the longest with good-quality pressure-treated wood and HDPE coming right behind.

Filling The Bed

How you fill the raised bed depends on how deep it is and what you want to grow in it.

If the bed is shallow, say only 30cm, then you will fill it with the appropriate soil mix.

If the bed is very deep, say 90cm, then you have the liberty to put in a layer of up to 30cm of whatever earth is native to your garden provided that it is not so heavy that it will prevent drainage.

Even if the bed is not quite so deep but is 60cm or more, you can still put in a shallower layer of your garden earth.

You do not need to try to improve drainage in a raised bed on top of soil, but adding a lower layer of gravel in a deep bed can be a good idea.

Indeed, the deeper the raised bed, the more quickly it will dry out, especially in hot weather, so I would recommend introducing vermiculite in the upper layer or topsoil, as Janice Shipp, a Garden Writer, explains:

“Growing in raised beds is a bit different from growing in the ground. I find raised beds dry out much faster so, in summer, you need to water them more often.

“My allotment is on clay, so a raised bed can be an advantage in the early part of the year if it’s been a wet winter and I want to get planting, but I’ve only got a couple on my allotment as I like to keep the layout flexible and you can’t easily change things if you put in a lot of raised beds.”

The soil you fill your raised bed with is really dependent on the plants you intend to grow in it.

We suggest you consult our plant-specific growing and care guides for precise guidance on this point.

In general, though, a balanced loam comprising sand, chalk, and some clay, amended with 20-30% organic compost and organic manure with a soil pH anywhere in the slightly acidic-neutral range will do very well.

You may lay a 4-6cm layer of mulch after your plants start growing.

It will protect plants from the cold in the wintertime as well as slow the surface soil from heating up and drying out in hot weather.

“I top my raised beds twice a year and sometimes after I’ve harvested a big crop,” says Emma.

“Leaf mould, manure, compost and even chopped-up old crops work great at replenishing the soil and mean that new crops benefit from new nutrients.”

Specialist Ornamental Beds

You do not need special raised beds for growing ornamentals.

It is just a question of the depth of the raised bed and the type of soil it should have.

A raised bed for growing ornamentals should optimally have a depth of about 45cm.

The kind of soil and soil pH that it should have depends on the particular ornamentals you intend to grow in the raised bed.

FAQs

What Goes On The Bottom Of A Raised Bed?

You do not need to put anything at the bottom of raised beds.

Avoid putting plastic sheets at the bottom otherwise the bed will not drain properly.

Does It Matter Where I Place My Raised Bed?

Yes, it does.

To begin with, the elevation of a raised bed exposes plants in it to the elements more than those growing at soil level.

Therefore, if you intend to grow such plants in your raised bed that are recommended to be sited in a sheltered spot, it is imperative that you place your raised bed in a sheltered location.

Therefore, if you are building a raised bed to grow particular plants in, then you need to site it according to any specific needs those plants may have.

How Long Do Wooden Raised Beds Last?

There is no hard-and-fast answer to this question.

How long wooden raised beds will last depends on four variables:

• The type of wood.
• Pressure-treated wood or ‘regular’ wood.
• Lining the walls with plastic sheets.
• How rainy, humid, and warm the weather is over a year.

For example, redwood will last much longer than pine, and pressure-treated wood will last much longer than non-pressure-treated wood (of the same type).

If the insides of the walls are lined with plastic sheets, the lifetime of the wooden raised bed will be extended.

The rainier, more humid, and warmer the weather over a year, the quicker the wood will degrade and the shorter the raised bed’s life.

Should I Line My Raised Garden Bed With Plastic?

You may certainly line the sides, though not the bottom, of your raised bed with plastic.

Whether or not you should do so depends on two variables:

• Is your raised bed made of untreated wood or timber?
• Is your raised bed made of wood or timber pressure-treated with CCA or other chemicals?

If your raised bed is made of untreated wood or timber, then you should line the walls – both inner and outer walls – with plastic.

This will shield it from the negative effects of wetness and damp soil, protect rot from setting in, and prolong the life of your raised bed.

If your raised bed is made of wood or timbers pressure-treated with CCA or other chemicals we recommend that you do not grow edibles in it but if you do so then you should line the inner walls with plastic.

You may also line the sides of your raised bed with plastic even if the walls are made of timbers that are pressure-treated with a safe, non-toxic compound or made of stone or bricks.

Just be aware that the plastic may tear if it gets scraped with a gardening implement, may shift and slide out of place after heavy rains, and will eventually wear out and degrade and will need to be removed.

So, avoid lining with plastic if there is nothing to be gained.