Newby seeks roof top gardening advice

johntyroApril 4, 2014

Last summer I built an 8' x 12' deck on the flat roof of my house in the boston area. This year, I want to surround (fence in) the deck with a series of containers for growing vegetables, herbs and some decorative plants. I anticipate tha the containers will be between 22" and 24" square on the inside with various depths dependent on use. The floor of the containers will have holes to allow drainage into a water reservoir below (plastic tub), a filler tube and for wicking of water into the soil above. The containers will custom built for attractiveness and will include legs to bring them to waist level for ease of access. With these remarks in view, I would appreciate comments on the following issues.

Recommend a good soil mix that will work well in a self watering environment and be light in weight. With respect to the weight, I'm hoping there exists a mix that will not exceed 64+ pounds per cubic foot (the density of pure water) when completely saturated (assumed worst case). There is no need to comment on the capacity of the roof as I am a retired structural engineer and will take care to address this issue. I'm more concerned about the weight that I will have to haul up to the roof.

With regard to the self watering system, should I use a column(s) of soil down into the water reservoir or rope for wicking. Is there a rule of thumb as to the area of wick to total area of the container which in my case will be close to four square feet. How about impact of soil depth. In general, do you think self watering is appropriate for my situation.

Can I be confident that 2' x 2' containers will be large enough to grow the largest tomato varieties (say beef steak or mortgage lifter). How deep for herbs, peppers, carrots, lettuce and flowers.

Note that I am a beginner in all this and will have many more questions as I move through this project. Would you recommend that I start a new thread for additional questions or just continue with this one.

Thanks for your attention.


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nil13(z21 L.A., CA (Mt. Washington))

If the worry is lugging container media up there, I would chose a lightweight hydroponic setup. LECA is relatively light. On top of that, you only have to carry it up there once. The container media that is heavy in organic matter is going to have to be replaced every couple of years. That means carrying it up, down, and then new back up again......

    Bookmark   April 4, 2014 at 3:08PM
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As a newby, I'm not that familiar with hydroponic gardening. Will I be able grow as great a variety of vegetables, herbs and flowers with it?

    Bookmark   April 5, 2014 at 5:02PM
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nil13(z21 L.A., CA (Mt. Washington))

You can grow pretty much anything with the right setup. I grow most everything hydroponically, though most people would never guess that because I use what would be called a non-recirculating "to waste" system. But that's a fancy way of saying I water plants in pots with fertilizer water, just like everyone else. If you use Al's gritty mix and fertigating you are growing hydroponically. It doesn't have to be a complex recirculating setup. What is important is that the plants are getting their nutrients primarily from the irrigation water.

Those recirculating systems get used when people are very concerned about the cost of fertilizer and water. That's generally not that big of a deal for a hobbyist, but when it's a business it sure is.

There are people growing all sorts of stuff from lettuce in 2liter bottles of solution (Kratky system) to Disneyland growing 30' rubber trees and bedding plants in huge concrete planrers filled with gravel (essentially Missouri Gravel Bed).

I have done a wick based system with perlite and sand. That particular medium and wick combination held way too much water. But I don't see why you couldn't get some kind of self watering thing to work. I am over the whole self watering container thing. I could never get them to behave exactly the way I wanted. On the other hand, timers, valves, and mains water allow for a lot of adjustment.

I live on a steep hillside with lots of stairs. I don't like schlepping compost up and down those steps, but I do it because the soil needs organic matter. When the organic potting soil is spent, I can just dump it in the garden and it's not a big deal. However, I have a lot of my propagation stock in gravel, so that I can reuse it without dealing with the stairs. I know if I were gardening on a roof, I would want to minimize hauling medium. I would probably use pumice and calcined clay ( or better yet Axis (diatomaceous earth)).

And if you're an engineer, a fun project is making a irrigation controller out of an Arduino, a relay board, and a 24v transformer.

    Bookmark   April 5, 2014 at 9:15PM
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nil13(z21 L.A., CA (Mt. Washington))

And if you do find a plant that really does want to be grown in a very rich organic medium, just grow that one plant in the rich mix. I don't grow everything in gravel.

    Bookmark   April 5, 2014 at 9:22PM
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I'm real interested in the hydroponic idea if it really means "no soil". I have already installed the plumbing to provide the necessary water. What are some of the advantages and disadvantages of growing plants using this method. Much of the discussion I've read about hydroponics talks about indoor growing with artificial lighting making me wonder if it is appropriate for outdoors on a roof. Can any one suggest a thread that will provide step by step instructions on how to grow tomatoes (big ones), peppers etc. using hydroponics.

    Bookmark   April 8, 2014 at 2:02PM
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nil13(z21 L.A., CA (Mt. Washington))

It's absolutely appropriate outside on a roof. You should search the hydroponics forum. You will find a buch of people growing all sorts of vegetables outdoors.

    Bookmark   April 8, 2014 at 4:10PM
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nil13(z21 L.A., CA (Mt. Washington))

Your best bet for tomatoes would be a dutch bucket drain to waste system like commercial growers use. For a recirculating system, flood and drain seems to work pretty well for people. It seems that typically, people stick one tomato plant in about a 5 gallon bucket and 1 pepper in a 2 gallon bucket.

    Bookmark   April 8, 2014 at 4:35PM
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