Garage-top garden

Witchhazel is blooming at my house, a sign that spring is nearly here. I’m planning my garden, which will be my second one ever, if it comes to fruition.

I started my first garden by reading piles of books. I spent the winter lingering over every kitchen garden book Amazon had to offer, littering my Sunset Western Garden Book with sticky flags, and studying the Maritime Northwest Garden Guide for tips on companion planting and bed rotation.

Spring came, and so did the annual edible plant sale at Seattle Tilth — the city’s organic urban agriculture hub — where I bought everything that looked interesting. But then I was stuck. I’d read all about gardening, but still felt I had no idea how to do it. I’d pulled weeds in my dad’s garden and plucked strawberries on my grandfather’s farm, but I’d never learned how to stake a tomato.

I was afraid of putting those plants in their beds, worried that I’d get everything wrong. They sat for a couple of weeks in their containers, until an imminent departure prompted me to just plop them all in the ground and hope for the best.

The garden wasn’t a great success, but everything was alive on my return 3 weeks after planting and as the season progressed we enjoyed a wealth of onions, a few cucumbers, a boatload of tomatoes, and one lonely pumpkin.

That was two years ago. Last year we were in the midst of a move in the spring and I never got around to planning or planting anything, but I had plenty of time to dream up the idea of sticking a garden on my garage (listed last month among our Ethicurean intentions for 2008).

For this garden, I’m seeking a lot of advice and assistance — not just about gardening, but also about engineering. I want to be certain to maintain the structural integrity of the garage, ensuring that it bears weight and sheds water.

Since it’s a new building which the prior owner, an architect, designed to hold a deck, I expect the garage will bear the burden of my project. I’m imagining it as a little urban farm, with vegetable beds, honeybees, and broiler chickens. I enlisted help from Colin McCrate, farmer-owner of Seattle Urban Farm to determine how much all that stuff might weigh. He sketched a few plans and provided some detail about materials, which I then passed along to a structural engineer.

As it turns out, the engineer doesn’t really care that I want a chicken coop and 300 lbs of hives and honey, he just wants to know what depth of soil to imagine spread over the whole thing so he can work his calculations. We’re stalled here for now, as we struggle to communicate (he wants me to name a depth, I want assurance that an imaginary depth is going to account for all the very real weight). Though I don’t yet have a definite answer, the engineer has said it looks like a very sturdy garage, and he thinks the weight should be fine.

The next step will be trading tar-paper for a green roof. There must be some product suited to the purpose. If the Seattle Public Library trusts the Ballard branch’s living roof to keep its 66,000 books dry, surely there’s a system that will protect our Honda. Nevertheless, this is the part that scares me, partly because I know so little about it, and partly because I imagine that it will be very costly. Of all the parts that could kill my plans, this seems the most likely.

All the planning aside, I’ll actually need to know how to grow a plant. I’m determined to surround myself with mentors this time. If I’m going to the enormous expenditure of effort to get a garden on a garage, it should at least be able to provide a hefty portion of our produce.

I’m concerned less about the plants, though, than the animals. My two-year-old and I are both excited by the prospect of chickens. Since she is allergic to eggs, we won’t have laying hens. I’m thinking meat birds. That raises logistical questions, like how to keep a rooster around for a breeding operation (the question is one of consideration rather than legality, as roosters aren’t outlawed in Seattle, but could nevertheless wake the neighbors) and how to establish a cycle that would put a bird or two on the table every month. But before I get that far, I’ll have to figure out how to kill a chicken, and whether I’m up to it.
Then there’s finalizing the layout, designing the chicken coop, building stairs to the garage roof, and hauling materials like lumber and soil up them. I’ll keep you updated. But I’ve almost talked myself out of the whole thing right there.

8 Responsesto “Garage-top garden”

  1. MamaBird says:

    Cool project! I am so envious. I live in a rowhouse in DC and have completely fantasized about a green garden roof — but my house is, um, not new. !! Please post again with your progress, I love hearing about this.

  2. ExPat Chef says:

    I am going to try an adaptation of Square Foot Gardening. He only calls for six inches depth in the boxes, outlines rotation methods, and then just some plants that require 12 inch depth. I am going that route this year. I just started the seeds for kale, romanesco, cauliflower and chard indoors. We’ll see how it goes!

  3. morfydd says:

    Oh, nifty. I’m thinking of doing something similar with my carport in Seattle, but it’s older and definitely needs to be structurally reviewed first. This year I’ve got a clear spot in the middle of the yard that will be the small veggie garden.

    Please do keep us updated!

  4. Great idea! I love your idea of rooftop gardening and I have a roofing material for you – Ferro-cement. We built our tiny cottage of stone and concrete with a ferro-cement barrel vault roof. Eventually the north and west sides will be bermed and the roof covered with soil.

    Because the roof is a barrel vault it is spacious inside yet incredibly strong due to it’s arch design. It is also something you can do yourself. Our family of five (me, wife, sons 14 & 9, daughter 3) built our own house all by ourselves. Adding knee walls along the sides allows the roof to flatten out. The garden beds can then go in the deeper areas off to the sides with the pathway down the middle where the soil would be thinnest.

    You can see some photos and articles about building our tiny cottage and the barrel vault roof at my blog:

    Yes, I know some people think concrete is not green but it is extremely green. It lasts – virtually forever. It won’t need to be replaced in 40 years and then again in 40 years and again in 40 years ad infinum. The concrete is good for thousands of years. When you put a garden on top of it you’re actually protecting the concrete so it can last even longer. Distributing the CO2 load over the life of the structure makes concrete (and even better, stone) one of the most green building materials. I shouldn’t be letting this tid-bit out because we earn part of our living here on the farm doing sustainable forestry… Ah, well… :) :) :)

    My ReCaptcha this time was “would Hurt” so now I’m wondering, “What?”

  5. PBrazelton says:


    What a clever idea – you certainly should go forward this this. When you’re old and gray you’ll want to have lots of good stories, and I guarantee you this one will provide many of them.

    Roosters are a nuisance, but they can be controlled to some degree by keeping them in an insulated coop. I don’t let our city flock out until 8 AM out of respect for those who sleep in the morning. This works fine, and our rooster cheerfully crows to the world all day long with no one to listen. Roosters DO crow all day long, so if you have a neighbor who works second shift you’ll have a serious problem.

    Your ‘green’ roof would probably follow the typical strategy of using an ice and water membrane to prevent water penetration to the structure below. You’ll have to make sure the layout accommodates water runoff (make sure you capture and reuse it!) and and protects the membrane. An well protected rubber membrane will protect your garage for many years, probably longer than you’ll live.

    Finally, regarding plants… learn to compost if you haven’t already. Your chickens will be a great source of nutrition for the garden, and home organic waste is always a good source assuming you compost it correctly. Because your garden will be physically partitioned from the ground below you’ll likely have few problems with predation or disease (well, whatever you don’t import with the soil), but you’ll also be isolated from the nutrient cycle. Compost will bridge the gap and keep your relatively thin soil base fertile.

  6. Charlotte says:

    Hi Jen — I’d second the compost comments — it was one thing I wondered about your layouts — where’s the compost pile? With chickens and garden waste you’d be surprised how fast you can fill one of those composters — on the other hand, you’re in Seattle where it rains, so maybe you won’t wind up with the kitchen midden I’ve got going in the backyard.

    The other thing is — have you watched how the light works in that space? It’s something you’ll want to think about when deciding which way to lay out the beds and where you’ll want to plant things. For instance, tall plants like tomatoes or beans or corn will cast pretty significant shadows … during a hot summer, that makes for a good spot to grow some lettuces, but you wouldn’t want to plant sun-lovers in those shadows …

    On the other hand — since you’ve already fessed up to overthinking — I’d encourage you to just go for it and see how it works out — you’ll learn more from experience than you ever can from planning — have fun — and I envy your chickens. With 2 bird dogs, I just can’t have chickens, as much as I want to …

  7. Molly says:

    I’m thinking you’ll need at least 12″ of dirt or you’re going to be watering your garden twice a day in the summer.
    I know of no way to be hatching out a bird or two a month. Hens go broody, sit on a clutch of eggs, and don’t start laying again until that hatch is a few months old. Better to raise a batch of meat-type birds, butcher them in one or two lots, and put them in the freezer.
    Consider a portable chicken tractor that is exactly the size of one of your beds. That way you can have your beds in rotation, with the chickens clearing out nematodes and other nasty things, and fertilizing one bed while you grow stuff in the others.
    Finally, some people who are allergic to chicken eggs can handle duck eggs just fine. I share my duck eggs with someone like that. Khaki campbell ducks are the greatest. And the drakes are quiet, not like roosters.

  8. tai haku says:

    Second the duck suggestion. Also have you ocnsidered just keeping hens and “renting” a rooster? If you get a popular breed of bird there will probably be a poultry fancier willing to lend you a rooster of the same variety for a few weeks after which you should get enough fertile eggs for a while and then you can give him back (perhaps with some chick/eggs as part of the bargain) and repeat the cycle later on.