Progress

As you can see from the photo the plants are actually starting to grow! I was getting impatient with few signs of progress but after about 2-3 weeks of minimal growth things picked up. After doing some research I have concluded that this is due to the fact that I didn't water the potting mix as I was making it, but rather only gave the newly repotted plants a drink from the top once they were already in the container. So for future plantings I will make sure the mix is moist to prime the uptake of water from the roots.

Construction

There are a few issues you have to contend with when creating a rooftop garden. Three of them are:
1) It's hot
2) It's windy
3) Some plants need support to grow

Since I can't bang anything into our roof without springing a leak I had to make a free-standing structure that can hold the buckets off of the hot tar and prevent them from being blown away. Also, this structure can help some of the plants to stay upright.

Covers

In order to stop the water at the bottom of the bucket from evaporating through the top of the soil, you need to cover the top of the soil with plastic. The easiest thing to do is to buy a large black garden tarp and cut it into squares that fit over the bucket. Then you cut an "X" in the middle for your plant and make another slice for the filling tube. Then you gently pull the plant and filling tube through their holes and tie a little twine or string around the lip of the bucket. Earthbox has a fancy elastic plastic cover but this method works just fine.

Planting

Then you put a little more mix in, make a hole deep enough for your plants, and throw them in there!

One thing about planting tomatoes: you want to plant them as deep as the first branches coming out of the stem. This will encourage stronger and more root growth.

You can top off the buckets with soil. It is most desirable to have a mound that peaks over the top of the bucket.

Fertilize

Now you can add potting mix nearly to the top. (It's also suggested that you water the mix as you put it in. I imagine this will make it easier for your plant's roots to start sucking water up sooner.) When you get near the top, make a little moat around the edge and put 2-3 cups of fertilizer in it. As the ingredient list on the blog says, all three of the numbers listed on the fertilizer should be above five.

Dolomite

Now you put a couple of inches of mix into the buckets and sprinkle some dolomite lime on top. This will help prevent the mix from becoming too acidic. It also contains magnesium and calcium, which plants need.

You can find dolomite here, or at most gardening stores.

Setup

Now that you have prepared the inner and outer buckets, packed the pond basket, and cut your fill tube to length, you can put them all together. The pond basket fits into the big hole in the inner bucket and extends down into the outer bucket, while the fill tube passes through its smaller hole in the inner bucket down into the outer bucket.

I've found it's easier to do the same step to a number of buckets rather than do a single bucket from start to finish. Here's a photo of six buckets that are on the way.

Tubing

A lot of places online suggest using plastic piping for your filling tubes but that seemed like a big pain to cut to length and transport (I don't have a car). So I got a bunch of this plastic tubing that is designed for water flowing into trailer homes. It's safer than pvc and less expensive than copper. I have no idea if the curve will affect anything (will mold grow?), but I guess we'll see! One benefit to using these is that you can cut them with kitchen scissors.

Packing

The next thing to do is pack the pond basket with your potting mix (as you can see I used the Miracle Grow blend for the potting mix). You don't want the mix to be loose in the basket because it may fall out into the water reservoir, which would impair the plant's ability to suck up water through the potting mix.

Cutting

The next thing to do is trace a circle on the bottom of the bucket around this nifty little invention that will act as your wick. These guys are called pond basket and you can order them here or you can make your own by drilling holes in plastic containers that used to hold hummus or yogurt. Then you cut out a circle just inside the line that you drew. And then cut out a smaller hole toward the side that will be big enough for the filling tube.

Diagram

So here's a quick diagram that shows how this two bucket planter works. The top bucket that holds the plant and dirt has a bunch of holes in the bottom and has an extension coming out of it that sits in the water and acts as a wick to draw water up into the root system of the plant. The outer bucket functions as the water reservoir and you fill it through a tube sticking out the top of the planter.

From what I've read this design gives plants the optimal amount of water and encourages high fruit yields. Also, this is good because you don't necessarily have to water it every day, but rather only when the water level drops.

This next photo shows the first step in getting the buckets ready, which is drilling a bunch of holes into the bottom of half of your buckets. I think I used a 1/4" bit.

Buckets

Then I started getting the buckets ready. I read a lot about self-watering container gardening, such as instructions from Earthbox, which you can find here, as well as from other places online, like here and here.

I put an ad on Craigslist for 5 gallon food grade buckets and got a bunch of responses. I wanted to pay $1-2 per bucket, which I thought was reasonable. You can also call bakeries and many of them will just give you their old buckets. One thing I would recommend: if you pay for buckets, only buy clean buckets. Scrubbing out chocolate or cherry pie filling from plastic buckets is not fun and takes away from what you want to be doing, which is gardening.

Another thing to watch for is that some buckets are 5 gallon and some are 4.3 gallon. If you're going to do tomatoes I've read that you should use the full 5 gallon.

I think I ended up with about 50 buckets in all.

Transplants

Once the seedlings got too big for their little discs I repotted the rest of them in spare pots and put them in the sun in my kitchen. They really started taking off but it was still too cold to put them outside.

Tomatoes

I also planted what will turn out to be way too many tomatoes. Here I've already repotted them from the discs into rolled up newspaper containers filled with potting mix (not soil--this will be important later). Newspaper worked great because it's free and easy and just the right size. You can read about how to roll newspaper planters here.

Seedlings

The first thing I did was buy a bunch of seeds and some of those little planter discs from Home Depot. You just add water and the discs expand and then you put a few seeds into each of these little puppies and in a few days little sprouts pop out. Here are sunflowers, peas, rosemary, basil.