Introduction: Cedar Raised Planter Beds Built for "Square Foot Gardening"
In this instructable I will cover the design elements, construction, installation and maintenence of two raised planter boxes I built for my vegetable garden. The two boxes are identical, with the small exception of the vertical trelises on each one for growing vining species such as peas, watermelon, pumpkin and cucumber.
The dimensions of each planter are 4 feet by 8 feet by 11 3/4 inches deep. The specific width and length is important, as these planters were built in order to employ the "Square Foot Gardening" method, which is supposed to conserve space, water, seeds and effort. the 4 by 8 foot dimensions also allow the planters to be built with minimal material wastage using nominal sized lumber.
The planters are built out of redwood cedar lumber. Cedar is very expensive (materials cost about $130 per planter) but it is naturally resistant to rot, termites and damage from sunlight. It's also very beautiful wood and a pleasure to work with because it's so soft. As an added bonus, sawing and drilling cedar fills your workspace with a pleasing aroma.
I tried to provide enough detail on methods and techniques that anybody should be able to build these and do a professional looking job; even if you're a beginner.
Please read on to find out how you too can build these planters.
Step 1: Some Notes About Choosing Materials
In order to build planter boxes identical to these you have three main options about which type of wood to use. Each of these types of materials have their advantages and disadvantages.
Standard Spruce/Pine/Fir Lumber:
This is just your standard everyday lumber that is untreated. This material is by far the cheapest way to build the planters (about 1/4 the price of cedar) but it will be vulnerable to rot, termites and damage from sunlight. Within a few months, the planters will turn an ugly grey color and may even warp and twist from exposure to sunlight. Even though they may be ugly, they will still remain strong and sturdy for many years, and you could always paint them to protect them from the elements.
Pressure Treated Lumber:
This is standard lumber that has been treated with special chemicals that prevent it from rotting. It's moderately expensive (about twice the price of SPF and half the price of cedar) but it's supposed to last for up to 25 years without rotting. The main downside to this material is that there is the widespread belief that the chemicals from the treated wood will leech into the soil and end up in your vegetables. I'm not sure if this is true but I will say that plant roots are supposed to have structures that prevent toxins from entering the plant, and I've been told about university studies that conclude that vegetables grown in pressure treated planters don't contain chemicals from the wood. You'll have to do the research and decide for yourself. However, pressure treated planters should definately be good for flowers and other things you're not going to eat.
This is by far the most expensive at about four times the price of SPF and twice the price of pressure treated. However you get the best of both worlds because you know that the wood isn't going to rot and you know that there's no nasty chemicals in your food. It's also the most visually pleasing option, and since my backyard is visible to most of the neighborhood, I decided on this option.
Step 2: Bill of Materials
In order to minimize wastage, two planters should be built because each one requires half of a 4x4x10 post and half of a 5/4x6x12 board. When you build one you end up wasting half of each piece (about $25 worth of cedar) but if you build two then you use it all. I'll give you the materials list for two planters but if you really want to build one then you and figure what you need. All of you Instructables users are intellegent enough people.
The required materials are:
5/4 x 6 x 12 decking board (9 pieces)
2 x 4 x 8 (4 pieces)
4 x 4 x 10 (1 piece)
Cedar post caps (8 pieces)
#8 by 3 1/2 cedar decking screws (one pack of 100 will do)
#8 by 2 cedar decking screws (one pack of 100 will do)
#6 by 1 1/2 cedar decking screws (one pack of 100 will do)
Note: The top caps that run along the sides of the planter boxes are purely decorative and optional. If you go without them you can leave out 2 pieces of 2 x 4 x 8. The same goes for the cedar post caps, not required just recomended.
Note: If you're going to build trelises for the planters you'll need and extra 2 pieces of 2 x 4 x 8.
Note: Be selective when buying your lumber. You're paying top dollar for the stuff so take the time to pick through it and get the best pieces. Hold the end of the piece up to your eye and look down the length of it. Make sure there's no big curves or lumps and bumps. Check for gouges, for wane, or knots and other imperfections.
The recomended tools are:
A mitre saw that can make a 6 inch crosscut (a blade size of at least 10")
A table saw
A portable roller stand
A drill press
A cordless drill
A drill bit set
A driver bit set
A rafter square
A tape measure
Step 3: Cutting the Lumber Into Pieces
Remember to square up the fence of your mitre saw before starting. This can be done with the rafter square (see photo 1). Don't rely on the reading from the scale for the mitre angle! Before you cut each piece of lumber make sure you cut a little sliver off of the end to square it up (See photo 2). Measure and mark accurately and make sure when you cut that the blade is on the correct side of the pencil mark (See photo 3).
First of all, out of each piece of 5/4 x 6 x 12 board you should cut one piece that's 93 1/2 inches long and another piece that's 45 1/2 inches long. Out of each 12 foot length of board you should have approximately 5 inches left over after you make your two cuts. Do this until you have 8 pieces of 93 1/2 and 8 pieces of 45 1/2 with one full 12 foot board left over.
The left over 5/4 x 6 x 12 board should be cut into a whole bunch of pieces 8 1/4 inches long. The exact size is not critical, it's just that 8 1/4 inches is one and a half times the width of a 5/4 by 6 board (more on this later). If your mitre saw has a cut length scale on the fence you may use that for speed (see photo 4), as the exaxt length is not critical.
Take a 2 x 4 x 8, square off the end and cut a 46 inch piece. Take the left over 50 inch piece and cut it exactly in half (make a mark at 25 inches and cut with the saw blade centered on the mark). Take the two 25 inch pieces and mitre the two ends on a 45 degree angle so that it can be used as a cross brace (see photo 5). Remember to use the rafter square to set the saw to a 45 degree angle (see photo 6), don't use the angle scale. Repeat the whole process for another 2 x 4 x 8. You'll have 2 pieces of 46 inches and 4 mitred cross braces of 25 inches.
If you're going to put on the decorative side caps, you'll need 2 pieces of 2 x 4 x 8 and rip both of them down on the table saw. Each 2 x 4 needs to be quartered (i.e. ripped in half along the 3 1/2 inch side and then ripped in half again on the 1 1/2 side). This should give you 4 pieces that are 1 11/16 inches by 11/16 inches if you have a 1/8 wide blade like I do. Set up the table saw by using the rafter square to square up the fence and a tape measure to position the fence (see photo 7). Do not rely on the distance scale on the table saw! You should also use a roller stand to make your ripping much easier (see photo 8).
Next, take your 4 x 4 x 10, square off the end and cut 8 pieces of 14 3/4 inches out of it. After you're done there should be about 1 1/2 inches of wastage left over.
Step 4: Preparing the Corner Posts
You now have eight pieces of 4 x 4 post that are 14 3/4 inches long. It's now time to mark and drill them in preparation for assembly of the planter.
First of all, an explanation of the methods behind my madness. The longest cedar deck screws I could find were 3 1/2 inches long. Since a 4 x 4 post is 3 1/2 inches deep, I can't drive a screw into them and have it bore into a piece on the opposite side. To solve this problem, I propose drilling halfway ( 1 3/4 inches) into the post so that the screw can penetrate further into the post and into the piece on the opposite side. The size of the drill bit used is not crirical but should be at least as big around as the head of the screw and not much bigger. Use your drill bit set to find a good size. Also, the drill bit used should have a tapered tip (not a brad tip). This is so that the bottom of the hole that you drill has a tapered shape and the screw will automaticly find the center. When starting the screw into the hole you won't be able to see the center of the hole but you will be able to "feel" for it.
The posts have to be drilled out on two adjacent sides. Make a line going up the center of the post on two adjacent sides. Starting from the bottom, use your tape measure and pencil to mark the locations for the holes along each line (See photo 1).
For one side use: 1 inch, 4 1/2 inches, 6 1/2 inches, 10 inches
For the other side use: 1 1/2 inches, 4 inches, 7 inches, 9 1/2 inches
It's important to stagger the holes from side to side. This is so that the screws don't intersect when they are driven at right angles to each other.
To drill the holes, a drill press is highly recomended for two reasons. The first is because you can set the stage up so that you know you're drilling straight down into the piece and not at an angle. The second is because you can set the depth of the hole and you can be sure drilling down to exactly where you want to. If you have to use a handheld drill all I can say is take your time and do your best.
Finally, each post needs to be marked on the two sides opposite the holes where the 5/4 boards will butt into them. A line should be made going up 1 1/4 inches from one side, it doesn't really matter which one. The reason is that the 5/4 board is 1 inch thick and a line going up the post 1 1/4 from one side is offset from the center by 1/2 inch. So when the edge of the 5/4 board is up against this line, the board is centered on the post but you can still see the line while your positioning the board (See photo 2).
Step 5: Put Together the Posts and Sides
You should try to do this on a nice flat surface such as a concrete floor or even a deck to help get the joints to fit together. If you don't have a flat surface you could get a sheet of plywood to lay on the ground and work on top of that.
The corner posts should be oriented so that the faces with the holes face out from the planter while the sides with the offset lines face into the planter. It will help if you start a 3 1/2 inch screw in each hole first. "Feel" for the center of the hole with the tip of the screw and drive it in until the head of the screw is just inside the hole. Take each 5/4 board and butt them into the corner posts so that the edge of the board is up against the offset line (See photo 1). Hold the board flush with the bottom and tight up against the corner post and drive the screw all the way in. When you feel the resistance increase all of a sudden you know that the head of the screw is tight up against the bottom of the hole.
Finish assembling the rest of the boards and corner posts. You should get all of the corners in place by doing all of the bottom boards first. Repeat the whole process with the top tier and you're done this step.
Step 6: Installing Cross Braces and Center Tie
Each cross brace is assembled using one 25 inch piece of mitred 2 x 4 and two 8 1/4 pieces of the 5/4 board. The 2 x 4 is butted into the 5/4 board and two 3 1/2 inch screws are passed through the board and into the end grain of the 2 x 4. The 2 x 4 is centered with respect to the height of the 5/4 board. The best thing to do is draw a line offset 3/4 inches from the center and then line the edge of the 2 x 4 up with this line. See the first photo of the assembled cross brace.
The cross brace serves two purposes. First of all it helps hold the two boards that make up each side of the planter together. That way they won't move in or out from each other when the planter is filled with dirt. Secondly, they hold the planter square and prevent it from flexing while being moved. Whithout the cross braces the planter is more likely to be a parallelogram than a rectangle. It's also built with a low profile so that it will be covered with dirt once the planter is filled.
Before the cross braces are installed the planter needs to be squared. The best way to go is to check the distance between opposite corners with a tape measure. Check one pair of opposite corners and then check the other pair. The measurements will be the same if the planter is square. If they are different, go to one of the corners with the longest measurement and give it a little kick towards the center of the planter. Keep checking and kicking until you get it squared up. After that be very careful that you don't move the planter until the cross braces are installed.
To install the cross braces position them into the corner with the 5/4 boards tight up against the sides of the planter. Put four screws into each piece of 5/4 board on the ends of the cross brace; one in each corner with two screws passing into the bottom side piece and two screws passing into the top side piece (See photo 2). Each planter should have a total of two cross braces with each one in opposite corners.
The center tie holds the two opposite sides of the planter 48 inches apart. It prevents the sides from bowing outwards when the planter is filled with dirt. It's also built with a low profile so that it will be covered with dirt once the planter is filled (See photo 3).
The center tie is assembled with a 46 inch piece of 2 x 4 and two 8 1/4 inch pieces of 5/4 board. Each end of the 2 x 4 is butted into the face of the 5/4 board and two 3 1/2 inch screws are driven through the board and into the end grain of the 2 x 4. The 2 x 4 is centered on the piece of 5/4 board. Make a line offset 3/4 inches from the center of the board and align the edge of the 2 x 4 with this line.
Position the center tie in the center of the 8 foot long side of the planter. Put a screw in each corner of the 8 1/4 piece of 5/4 board with two screws passing into the bottom side board and two screws passing into the top side board (See photo 4).
Finally, take a couple extra 8 1/4 inch pieces of 5/4 board and secure them to the inside of the planter in the same manner as the cross braces and center tie (See photo 5). The most important places are on the long sides of the planter near the corners without cross braces (See photo 6). This will prevent the two boards that make up the side of the planter from moving away from each other
Step 7: Installing Post Caps and Side Caps and Laying Out the Grid+
The post caps are easy enough. Just use a scrap piece of board to use as a "feeler" strip to help you center and square up the cap on top of the post and secure with a couple of 2 inch screws (See photo 1). One cap on the top of each post Bob's your uncle.
The caps for the sides are almost as easy. First, take the strips that you ripped down on the table saw and cut them to length. It should be two pieces 93 1/2 inches long and two pieces 45 1/2 inches long for each planter. Each strip should have one rounded corner from the original corners for the 2 x 4 before it was ripped down. I recomend placing this rounded edge facing up and to the outside of the planter (See photo 2). The strips can be a bit frisky at first so I temporarily secured them with a few 1 1/4 inch 18 guage brad nails before I screwed them down with 1 1/2 #6 screws.
The screws should be positioned every 12 inches from the inside edges of the planter. They should not be driven all the way in but the tapered part of the head should be left exposed so that jute twine can be wrapped around it. This is so that jute twine can be used to mark off a 1 square foot grid inside the planter for the "square foot gardening" method (more on this later).
Take your tape measure and butt it into the post (See photo 4). The post is 1 1/4 inches proud of the inside edge of the adjacent wall so your pencil marks have to go back 1 1/4 inches from each foot marker on the tape. The example shows a mark made at 10 3/4 inches for a total distance of 12 inches from the adjacent wall. Your marks should be spaced one foot apart from there. Repeat for all sides.
Next you should mark the locations for your pilot holes. You can use your rafter square to draw a perpendicular line at each of the pencil marks you made. Then you can use the measuring scale on the square to find 1/2 from the edge of the cap and make another mark there (See photos 5 and 6). You have then effectively made a "crosshair" for your drill bit to go into. Repeat for all sides.
Next drill pilot holes in the middle of each crosshair. I recommend a 3/32 drill bit for a #6 screw. Make sure you drill straight down, most cordless drills have a spirit level built in to help you with this task. I would also recommend using your drill press to make these pilot holes before you install the caps. I didn't use mine because it gave up the ghost shortly after I finished drilling out the posts and It's not back from the repair shop yet.
A #6 by 1 1/2 inch screw should go into each pilot hole. However you should leave the head of the screw sticking out a bit. If you have trouble precisely driving a screw with a drill, you should use a manual screwdriver. While driving the screw make sure you press down really hard on the cap or else the screw may draw the cap away from the side board.
Now you can use the screw heads to make a 1 foot grid with some garden jute twine. Start by tying the jute onto a screw head near one of the corners and then wrapping the jute around the screw heads back and fourth across the planter. The example photos in this step show the grid temporarily installed. This shouldn't actually be done until the planter is filled with soil and you're ready to plant your seedlings.
If youre not going to use the "Square Foot Gardening" method, you could drive the screws in all the way. This will make screeding off the soil easier for you when you fill it too.
Step 8: Placing the Planter Beds
You want the planter to get as much sun exposure as possible (unless you're planting a shade garden). If you live in the northern hemisphere that means it should be located on the south side of any large objects on your property such as a house, garage, shed, patio, etc. If you have no choice but to locate it to the north of a large object such as when you have a north facing backyard, you should put it at least as far away from the object as the object is tall. For example, it should be placed 12 feet away from a 12 foot high shed. When in doubt, bring the planter to a prospective spot and leave it there on a sunny day. Check it every hour from morning to evening to see if it ends up in shadow. You can get away a couple hours of shadow in the morning or evening but it should be in full sunlight all afternoon at least. As an example, tomatoes need at least 6 to 8 hours of direct sunlight per day.
Once you have a good spot picked out you can pretty much just lay the planter there and start gardening. You don't have to worry about the condition of the soil in that location or the amount of drainage because the planter takes care of all that. However, you should put down some landscaping fabric and secure it with the appropriate ties first. This will prevent weeds from growing up into your planter.
I've seen some people stake the corners on the inside of the planter too. This is supposed to prevent it from moving around although I can't imagine how that could happen with hundreds of kilograms of soil inside it. You can decide if you want to do that or not.
I'll post more about this project as it develops. I need to wait for the ground to thaw out before I can start preparing my site. For now I hope I've given you some knowledge and insentive towards building your own raised planter beds. Thank you for reading and constructive critisism is always welcome. Happy building!
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