How To Build A Raised Garden Bed

Raised bed gardens don't exactly have much to do with lawn care but one thing that can help your lawn look better is to have it be part of a nice landscape plan.

This post isn't an instruction on how to build a particular type of raised garden bed. It is the information you need to know to be able to build any size or type of raised garden to suit your needs.

Why Build a Raised Bed Garden?

A raised garden looks nicer and makes your landscape look a little more organized and can take up less space, leaving more room to grow grass. If you don't mulch your beds weeds can grow and then spread into your lawn. Vegetable gardens in particular don't always get mulched and can become a great place for weeds to take root.

If you have a hard time growing certain plants or vegetables, a raised bed allows you to add any type of growing soil you'd like avoiding the hard work of trying to remove or improve the existing soil.

A good book on growing vegetables and other edibles in raised beds that is great for small backyards is the All New Square Foot Gardening.

Why Build When You Can Buy?

Most people use raised beds for their vegetable gardens. Besides being able to grow your own organic vegetables, one of the big benefits of vegetable gardening is saving money. Unfortunately, even simple raised beds are quite expensive, costing $150-$200 or more including shipping.

With a few simple tools and some lumber you can buy locally, you can make your own for a lot less. A raised bed is just a 4 sided box and very easy to build. A little time, a drill, some screws and a saw is basically all you need. You can even do without the saw if your lumber yard will cut the pieces to the size you need. Helps it fit in the car too.

Maybe you don't want to build your own. You don't have the tools or the time I did manage to find an affordable raised garden bed. The Suncast RB448 Raised Garden Kit is only $50 and includes Free Shipping from Amazon. The bed is made of plastic and easy to assemble. It is 4' x 4' and 6" high. You can stack them to make a higher bed and even arrange multiple kits into different shapes. You can still make your own cheaper out of wood but the Suncast Raised Garden Kit is made out of steel corners and plastic sides which will not rot or be attacked by insects. If you want to reduce the size you can cut down the side pieces.

What To Build Your Raised Beds With?

You can use many things to build your raised beds, bricks, pavers, concrete blocks, poured concrete, plastic or wood.

Bricks, pavers, concrete blocks and poured concrete are more expensive and labor intensive. If you have access to free material it may be worth it but I'm focusing this post on dimensional lumber since it's what most people will choose to use.

When it comes to lumber, there are a few options. You can use regular construction lumber (spruce, douglas fir, pine), cedar, composite or plastic lumber. Do not use pressure treated lumber. The old chemicals they used to use in pressure treated lumber help it resist rot and insects so that it would last longer outdoors but the substances could leach out into the soil. The new pressure treated lumber is safer but there are still concerns. You also don't want to use PVC boards as the chemicals in that may leach out over time.
Spruce, douglas fir, pine are not resistant to rot and insects but are the most affordable option. They may only last 2 years or so before they start to decay. Treating them with a safe, non-toxic sealer such as raw linseed oil will help them last a little longer.

Cedar is the best natural wood choice for raised beds because it weathers well and is naturally resistant to rot and insects. A cedar raised bed could last 10-20 years. More if treated with llinseed oil. It weathers to a nice gray color but you can also paint or stain the outside to get a different effect. Some think cedar is too expensive to use in a raised garden and prefer to use cheaper lumber. That isn't the case. Cedar, like most wood, comes in different grades. High grade cedar used for furniture is expensive but there is lower grade cedar (knotty or construction grade) that is a very affordable option and will save you from having to rebuild your beds every couple of years or so. You might need to go to a good lumber yard to find it but it is available in many parts of the country. Lumber yards that provide fencing material should have it.

Composite lumber is wood particles mixed with a plastic resin. They last a very long time but are going to be more than cedar. Composite boards don't need to be sealed, are made from a lot of waste material and can be found at any of the big home improvement stores such as Home Depot and Lowes.

Plastic lumber is often made from HDPE (high density polyethylene. Recycled HDPE is made from recycled milk jugs. It is a safe material to use, a bit expensive but will last a long time. The problem is that it's not as easy to find and since it's heavy, shipping is not cheap. Stick with products made from polyethylene (HDPE) and not polystyrene or PVC as polyethylene is safer.

Lumber Dimensions

When you plan out your raised bed, you need to be familiar with the common types and sizes of lumber. It can be a bit confusing because the name does not tell you the exact size. For example, a 2x4 (two by four) is not 2" by 4" it's actually 1.5" x 3.5". It's important to know the sizes of the different types of lumber available because you don't want to make any lengthwise cuts. It is difficult unless you have a table saw. Restricting yourself to cutting for length will make things much easier.

If the lumber is labeled "rough sawn" it may be truer to size. It doesn't hurt to bring a tape measure to make sure you're getting what you think you are.

What Size Wood?

First, lets discuss thickness, the smaller number. 1x Lumber is only 3/4" of an inch thick and probably not the best choice, especially if you are planning a long or very deep raised garden. 5/4 lumber is 1" thick and should do well up to around 10" deep if the sections are 4' long or less. 2x lumber is the best choice because it will be stronger and even if it starts to rot it will last longer. 2x will be more expensive and I would recommend it if you're on a tight budget unless you're using composite lumber. 5/4 should be fine in composite and should be much cheaper than 2x composite lumber. 5/4x6 lumber is commonly used for deck boards and should be easy to find.

The next issue is the desired raised garden depth. If you want a 6" deep garden you can use 2x6 for the sides which will give you a 5 1/2" depth. You can also add a 1x3 or 1x4 laying on it's side like a picture frame around the top which will give you a total depth of 6 1/4". You can also stack two 2x4's which will give you 7" or a single 2x8 which will give you a depth of 7 1/4". If you want a 9" depth you can go for a 2x6 on top of a 2x4 or a 2x10.

For aesthetic reasons you might want to try and stick to the same size boards or come up with a pleasant combination. You also don't have to worry about getting it exactly the depth you want. You can have the soil come up level with the top of the bed or 3/4-1" below it.

How Deep Should a Raised Bed Be?

According to Mel Bartholomew, the author of Square Foot Gardens, 6" is enough for most plants if potted in a good growing medium. Plants only grow as much roots as they need. Mel recommends a mixture of 1/3 compost, 1/3 peat moss and 1/3 vermiculite. This combination will give you growing soil high in organic matter, full of nutrients and with good water retention. This will make it easier for the plants to get available nutrients and won't need to dig very deep roots to try and find what they need.

Some root vegetables will need deeper soil but you don't need to make all your beds the height to accommodate one or two crops. You can just create a section that's higher in a bigger bed as shown in the illustration. This way you'll not only save money on lumber but you'll also save on the material you use to fill the bed.

You can make these tiers any size you want and they don't have to be the entire width of the box.

How Big Should the Raised Bed Be?

That's going to be a matter of preference and how big your hard is. One good recommendation is to have one side not be longer than 4' if you can access it from both sides. That makes it easy for you to reach into the garden from either side without walking on it and compressing the soil. If you are placing the bed where you can only access it from one side, then keep it to 2' so you can get to everything for maintenance.

You can make it as long as you want but for vegetable gardens, it's nice to have multiple beds with 2-3' of space in between them to make it easy to access each bed from different sides. If you're following the Square Foot Gardening method outlined in the book, you will want to keep your beds in whole feet. So 2x2', 2x3', 3x3', 3x4', 4x4', 4x6', 4x8' etc would be good sizes but don't worry about deviating a little bit to fit your space properly.

Raised Garden Styles

What you want your raised garden bed to look like is a personal choice. Below are three basic styles you can choose from They are all relatively simple to build.

Plain Raised Garden Bed

The plain style raised bed is a simple 4 sided box. This is a very simple box to build consisting of only 4 pieces of wood that are screwed together.

If you want a square box, keep in mind that not all of the pieces are going to be the same size. The front and back will be larger than the two side pieces.

For example, if you wanted to build a 4x4' raised garden box out of 2x8 lumber, so that the interior of the box is 4' x 4', the front and back pieces would be 51" long and the side pieces would be 45". As you can see from the photos, we're just making butt joints which means to have a perfectly square box, we have to account for the thickness of the material.

If we were making the same sized box out of 1x6 lumber, we would need 2 49.5" pieces and 2 46.5" pieces. Basically double the thickness of the material and add it to the interior size you are looking for for the long pieces or subtract it for the shorter pieces.

Lipped Raised Garden Bed

The lipped raised garden bed is just a plain raised garden box with a frame around it. The frame is composted of a thinner stock of lumber that is mounted on its side.
Cutting the corners on a 45 degree angle will give you a nicer look than putting the pieces together. To do this you can use a compound miter saw but for a few cuts, a miter box and saw will do fine. Click on the photo on the right for more details. Amazon has one for around $12 with free shipping. It will help you cut perfect 90 and 45 degree corners. The 90 degree setting will help you get nice clean cuts for your butt joints as well only fit 2x4 lumber or smaller.

In addition to a powered compound miter saw I also own a manual one which I still use frequently. It's very easy to use and you don't need to worry about power.

All 4 pieces should be the same size but make sure to measure the exact length on the inside of the box from one corner to an adjacent one. In our 4x4' example, using 1x3 lumber for the lip. The piece will be 48" on one side and 53" on the other if every thing was perfect.

Post Style Raised Garden Bed

The post style raised garden bed is my favorite because I find it more interesting because it has some varying height and thickness. It's going to be a little more expensive to build and take a little more effort but not much more. One other thing to consider is that the post style bed is that the outside size is going to be about 5" wider than a plain style bed. One benefit is that it looks nice attaching multiple short pieces in a long bed, for example a 4x12' bed with 4 posts along the 12' side, 2 on the corners, 2 spaced equally in the middle.
It's comprised of 4 4x4 posts that are cut 2" higher than the 2x side pieces. If you were using 2x8 lumber for the sides, you would cut your posts to be 9.25" high. The 2x sides are attached to the middle of the 4x4 posts so there is 1" of 4x4 on either side of the 2x.

All 4 side pieces will be the same if you're making a square bed. In our 4x4' example we would need 4 46" long pieces of 2x for the sides.

I like to take a 1" spade bit and drill a 2" deep hole in the center of each 4x4 post. This gives you a hole where you can slide 1/2" PVC pipe to build a frame for a cold frame or netting. To keep water from collecting in the hole when you're not using the PVC pipe frame, slide a decorative post cap on top, such as the ones shown below. You can even try solar powered post cap lights.

Determining How Much Wood You Need

This is where some people get into trouble. The first thing you should do is make a drawing of your raised bed.


Step 1 - First draw a rectangle of the top view of the size you'd like the inside of your bed to be. Noting the length and width of the bed. It doesn't have to be to scale but you can use graph paper if you have it to make it more precise if you want.

Step 2 - Draw the top view of the pieces of wood you will need around the first rectangle. You can see an example for the plain bed and the post style bed below. The lipped bed is the same as the plain bed.


Now we can visualize exactly how long each side piece needs to be.
In the case of the plain bed:

Front/Back length = Length + (2 x thickness of board) Sides length = Width - (2 x thickness of board)
For the post style bed:

Front/Back length = Length - ( (Width of Post) - (thickness of board) / 2) Sides Length = Width - ( (Width of Post) - (thickness of board) / 2) Height of post = 2" + width of side boards.

Once you know how many boards you need and how long each is, you can figure out how many pieces of lumber you need to buy. Also keep in mind you will lose about 1/8" per cut due to the width of the blade.

Lengths of lumber usually come in 8', 10', 12' and 16' but you should ask your lumber yard what they carry.
Let's use our 4'x4' example again. We'll make a plain bed using 2x8 cedar. We know we need 2 51" prices and 2 45" pieces. 51 + 45 is 96 which is 8'. We can purchase 2 8' lengths of 2x8 cedar. We're going to be off by an 1/8" due to the saw cut but that's not enough to justify the cost of an extra board. Below you can see the cut diagram showing how each board will be cut to get the pieces we need.


If you have a power miter saw you can make nice straight cuts or you can use a circular saw. If you take it slow you can get straight cuts with a hand saw or you can ask your lumber yard to make the cuts for you. There is sometimes a fee for this. Usually around $1 per cut. Sometimes these are called "convenience cuts" which means they may not be exact. They are cuts to make it easier to fit in your car but if you get someone good making the cuts they'll be very good. If they don't charge per cut and the person doing the cutting does a good job of measuring and cutting feel free to tip.

How to Attach The Pieces

One way is to use 3" deck screws into the face of one piece through the side of the other. You want to use deck or stainless steel screws because they won't rust outside. You should pre-drill holes for the screws to keep the wood from splitting.

It's easier if you have someone helping you so you can keep the pieces square or you can use a corner clamp like the Kreg KHC-90DCC 90-degree Corner Clamp pictured right.

Instead of screwing directly into the boards you can make pocket holes which will be less noticeable. I bought a Kreg MKJKIT Mini Kreg Jig Kit to build some cabinets and I have found many uses for it. In fact I try and come up with uses for it. It makes a very strong, concealed joint. Pocket holes with the Kreg Mini Jig are very easy but you do have to take some time to align it properly. If you plan on using it often you may want to consider one of the other Kreg Pocket Hole Jig Systems which are faster to align. You'll also need a clamp to hold the jig to the wood, a 12" Irwin Quick Clamp will work fine.

Kreg also makes their own screws for use with their pocket holes and I've never used anything but their screws. Kreg makes weather resistant Blue-Kote screws. You'll need different sized screws depending on the thickness of the side pieces you use. Use these links for the proper screws if you plan on using 1x and 5/4 or 2x lumber for the sides of your raised bed.

Kreg also makes plugs to fill in the holes and give you a finished look. The plugs are available in different species of wood, including cedar, as well as plastic.

Painting/Sealing Your Raised Garden Bed

Untreated wood will deteriorate faster outdoors than untreated wood. If you'd like you can use pure raw linseed oil or 100% Pure Tung Oil. Linseed oil is made from flax seed and is non-toxic. It is not a UV inhibitor so it will not prevent your wood from changing color as it ages.

Another option if you'd like to give your beds some color is to use Milk Paint on the outside of the boxes. Lifetime Wood Treatment also claims to be a non-toxic wood preservative but I haven't been able to determine its ingredients.

Installing Your Raised Garden Bed

Installing your newly built raised garden bed is simple. Just pick an area, dig out any grass and place your bed frame on the soil. Use a level to make sure it's level.

To help secure the bed, screw in 2 screw eyes with an inside diameter greater than 5/16" into each post. One towards the bottom and one in the middle and drive a landscape spike through the screw eyes and into the ground. The weight of the beds and growing medium will do most of the work keeping it in place.