Galvanized Water Trough Raised Bed Design Help

lowie(7)May 20, 2013

Hi There,
I am looking to build five raised beds by using the galvanized water troughs as the containers. I live in the Pacific Northwest (Western Washington) and have had luck with the wooden raised beds in the past.

I'm stuck in between two designs and would love advice from people who know what they are doing to help figure this out.

The first design is a wicking one, seen here: h-gardening.pdf
The design looks great but the problem is it's obscenely expensive to get the poly mesh she references here. I can't find it for any less than $250 for the 5 beds, plus $100 for shipping. That, on top of the price of the troughs makes it a spendy endeavor. I am intrigued however by the self-watering system, only having to fill it through the feeder tube and not having to drill/seal the holes (so the galvanized metal won't rust).

Option two would be a more standard design with a drip irrigation system. Also pricey but I have a lot of the supplies and it's fairly simple. The problem I'm having, however, is with what goes in the bottom. I've read on here to not do a coarse gravel as it doesn't help with drainage. Do you recommend just the soil throughout? With our wet weather I want to make sure the soil doesn't get too compacted. I do have one of these that is two years old with raspberries which is doing fine (and is all soil), but my personal opinion is that raspberries have no problem growing in anything.

Regardless I will put them on a leveled base of pavers so they don't sit directly on the soil. I will also likely put gravel in the middle of the structure (if it will help with drainage). I will also be coating the inside with a water-based rubberized paint to protect from the zinc leaching which is a slight risk, but still better to do it right the first time.

Any recommendations are appreciated as is experiences with this.


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lonmower(zone8 Western Oregon)

Soil compaction will be a problem and I don't have an answer for that. A larger problem will be amount soil that will be above ground. Down here in July and August we have stretches where the ambient temperature is in the 90's and above. That metal will get Hot Hot. Overheating the soil and the roots of whatever you have planted. Troughs might be like a good idea...but I don't think so. Stay will wood raised beds.

    Bookmark   May 20, 2013 at 7:25PM
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nancyjane_gardener(Zone 8ish North of San Francisco in the "real" wine country)

Check out the container gardening forum. They know all the formulas etc for the best drainage, etc.
I have a friend who does most of her winter stuff in a huge galvanized round trough and everything does fine. Not sure about the summer stuff, though.
I guess it would partly depend on how large the containers are and close to the edges you're planting? Nancy

    Bookmark   May 20, 2013 at 8:21PM
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I'm located near you :).

My garden currently is mostly in huge raised beds, 24" tall. I filled one with half fines (smaller than sand), and half composted 'manure' (which is really mostly composted sawdust bedding). The other I used half sand and half municipal compost.

Both of these mixes provide excellent drainage. The fines mix is the best, if you can get the stuff. Try your local gravel quarry. It has a wonderful 'sandy loam' texture. The sand is a bit TOO good of drainage :).

Using these blends, I have not had to do any supplemental fetilization yet, after 8 years.

As for temperature, most varieties won't mind it but some will. I would suggest you get very large troughs, and plant stuff that does well in small containers at the edges where it's hot, and those that hate containers in the middle.

Forget the wicking and the gravel!

    Bookmark   May 20, 2013 at 9:35PM
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Nila -

THANK YOU! This is exactly what I was looking for. I assume landscape fabric over the holes in the trough and below the fines will still allow good drainage but prevent the fines from escaping?

The rest makes sense.

    Bookmark   May 20, 2013 at 9:56PM
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How did your galvanized water troughs work out? I'm a Seattle resident who would like to try the same but am utterly new to gardening (this is the first year I've owned a house with a substantial area in which to give it a try). We'd like to have one area with raised beds and another with galvanized tanks as beds. Not sure how to proceed with either but the tanks really have me stymied. Are small holes drilled in the bottom adequate drainage given our PNW rains? Or would it almost be better to cut out the bottoms of the tanks? Is it safe to grow food in galvanized metal? I know some zinc consumption is safe but I think the cadmium is a greater concern.

Nila, Could you elaborate on your soil instructions? Are you recommending mixing these 2 components are layering them in some manner? Would you recommend this same mixture for other types of raised beds as well?

Thanks guys! Hoping the GW community will take me under their collective wing and help grow a new gardener!

    Bookmark   July 14, 2013 at 7:01PM
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Hi Tess :)

I would be inclined to cut a giant hole in the bottom of the tank, personally. Like, remove most of the bottom, and cover the opening with landscape fabric.

If you choose to drill holes instead, make sure they are big enough. You have to at least be able to put your finger through each hole, and 2-3 inches diameter is better. Water doesn't drain well through small holes when dirt is involved, because of surface tension (not to mention clogging).

Don't layer the soil. You don't have to mix it perfectly, either. Put in a shovelful or two of one component, then a shovelful or two of another :).

Personally, I don't worry about soil compaction in my bed. Sure, the sandy mixes are very dense. But worms plus gardening means lot of soil gets moved around. And the plants are happy.

HTH :).

    Bookmark   July 15, 2013 at 1:42AM
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