Thursday, August 21, 2014

Project: Large Wooden Planter for Green Onions

In my last post, I mentioned that while Heather was waiting for surgery over the late spring, I built her some planters and did a lot of gardening work so that she would have a nice place to rest and recover outside. I think those planters deserve a little more elaboration.  They were very simple and fairly inexpensive to build, since I made them out of 2x4's and Western Cedar. There are a few things I would do differently now that I've made them, but it's the kind of stuff I can add in later as a retrofit.

The basic idea was to make a simple but interesting planter to place on our driveway. We have a large concrete driveway that's covered in potted plants. Our soil here at the house is almost solid clay and just doesn't play well with a lot of vegetables. I wanted to make a large raised planter so that it would provide some screening that Heather could sit behind while also providing enough depth for the green onions to grow happily in.


This is the basic design I came up with.








Overview

The planter is made from just a few basic components.
  • The legs.
  • The top and bottom rails of the planter.
  • The vertical slats.
  • The bottom slats.
  • The decorative top moulding (OPTIONAL).

Part 1: Legs

The legs are made from 4x4 lumber stock. Use non pressure treated wood, since you'll be growing things in this planter. If it's just going to be used for decorative plants, then go ahead and get PT lumber since it will withstand rot more effectively. In my case, I used scraps of 2x4 lumber and secured them together using glue and screws. Either way works just fine. Cut four legs to size.


Part 2: Rails

The rails are made from 2x4 non pressure treated lumber. Get the straightest you can find, but if they're a little cupped it's not the end of the world. This planter is big enough and heavy enough that it's pretty forgiving of minor imperfections in the wood, and since it's an outdoor functional landscape piece, I didn't worry too much about knots or nicks.

You will need 8 rails in total: 4 short ones for the sides and 4 long ones for the front and rear. My long rails were 48" and my short ones were 18".

Once you have the rails cut, you need to put a dado down the middle of it to accept the side slats. I used a 3/4" straight cutting bit on my router table and cut the dado 1/2" deep. If you have a dado blade on your table saw, that would be easier to use for this step.

I then took a cove bit and carved out a simple cove on the outside face of the rail. For the bottom rails, I coved the upper face. For the upper rails, I coved the lower face. This made the rails frame the slats nicely. This is a purely decorative step and can be skipped.


Once all the rails are cut, you can install the lower rails onto the legs. Don't install the upper ones just yet. I secured my rails using 2 1/2" pocket screws from below, but you can fasten them any way you would like. Using long lag screws would definitely be more secure, as would mortise and tenon joints, but I'm cheap and I'm not good enough with MT joinery yet to pull it off. Next time, I would do a MT joint, but 2 x 2 1/2" pocket screws in each side of each rail is holding the planter very well so far. I expect those to begin to fail after 2 or 3 years however, due to rot of the wood from the moisture. A tenon joint would last a lot longer in these conditions.

With your lower rails installed to the legs, the carcass of your planter now looks like this:


Believe it or not, you're already about half way done! Now it's time for....

Part 3: Slats

You're going to need a lot of slats, and this is the biggest expense for the project. You can cut this cost in half if you want to get standard 3/4" stock and resaw it in half. I wanted to but I'm still working on tuning my band saw well enough to be a reliable resawing machine, so I just went for full thickness. Since this planter isn't very tall, a 3/8" thick slat will provide more than enough lateral strength to hold back the soil. If you do want to resaw your slats, make sure your dado in the rails is 3/8" rather than 3/4"!


The bottom slats are made of western red cedar in order to better resist rot. I made mine 20 3/4" x 3 1/2".  I definitely do NOT recommend resawing these down as they will be bearing the full weight of the wet soil above them. In the case of my planter, that's about 400 lbs.

You will need 2 slats with notches cut out of them to fit around the legs, and then 12 more without notches. I placed them with a 3/8" gap between them for drainage.

Now you're going to need slats for the side. There will be a total of 44 side slats, measuring 19" x 3" for this planter. The real one I built is a bit taller- the slats are 23 7/8" tall each, since I could then get 4 exactly from each 8" cedar board. In practice, I've found that makes my planter a little taller than I like when the plants are fully grown, since I do a lot of hand watering from rain barrels with a watering can, and I then have to lift and hold the can up at mid chest level for long periods. With 19 inch slats, you'll get 5 slats out of each 8' cedar board (or 10 if you resaw it). Adjust the measurements to come up with a height you like, but don't forget to account for the height of the plants that will go into the planter!

Once you've cut the side slats, you can drop them into the bottom dadoes and place the lower bottom slats into position.


Then install the top rails the same way you installed the bottom rails.


At this point, your planter can accept soil and plants. I decided to make a decorative moulding for the top to spruce it up a little bit, and to provide more room to set smaller planters on it.

Part 4: Moulding/Trim

The final components are two pieces of moulding. I chose a compound moulding because I love the way cove and roundover looks, and I have the right sized bits already. You can choose any moulding you'd like, or you can omit this step entirely- it's purely decorative.

The first (lower) piece of moulding is a simple cove moulding. We'll be putting a roundover on top of that to create a classic compound profile.


These are the dimensions of the lower cove moulding.

... and these are the dimensions of the upper roundover moulding.

Cut out your pieces and miter them to fit as you'd like. This step is really open to modification- try using thinner stock to create steps on the inside of your planter for a cool shadow effect.

Secure the cove moulding with screws down through it into the legs.

Secure the roundover moulding with some longer screws from below.  Be prepared for this wood to swell a lot so your edges may not line up well over time. I went with a simple butt joint with a roundover on the first version of this planter for this reason, and it's held up pretty well.  As always, tailor the design to your own aesthetics and desires.

Conclusion

Here's the planter right after I built it and filled it with soil and transplanted a few onions into it.

As you can see, it's pretty easy to build a big planter with lots of room in it for tightly growing vertical plants like green onions, and it doesn't have to break the bank. This planter cost me less than $100 to build in total.
  • 5 2"x4"x8'. 2 for the 4 legs (or 1 4x4) and 3 to make the rails.
  • 13 1"x4"x8' western red cedar boards. 9 for the side slats and 4 for the bottom slats.
  • Fasteners of your choosing (I used pocket screws since I've been playing a lot with a Kreg Joiner lately.)
  • Trim for the top. This will vary depending on what you want to build. A simple, single-layer trim with butt joints will take 2 or 3 more cedar boards.

And here's the same planter a few weeks later after the first crop of onions began to grow. The 2nd is just barely visible as seedlings between the big guys.

Have you made a simple planter for your home or garden?  I'd love to hear about it in the comments!


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