cement raised beds

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I have a question I hope SOMEONE will be able to help me with! Either an answer that makes sense or where to look for it. Here 't is: We are getting ready to add more permanent beds to the garden, and fix the beds we already have. The plan has been for a cement wall around each bed, under ground to try to stop gophers and quack grass, and above ground to make for good seating while working and also so rabbits can graze between the beds without having access. My question is, what about the cement? I have heard from many sources that it may not be a good thing, but no one has any reasons why. Are some cements different from others? such as, Redi-mix has additives that Portland cement doesn't? Any Ideas?? Where to look??? Thanks! I appreciate all help, Fran

-- Fran Ogren (trumpkinland@plix.com), August 10, 2001

Answers

Fran, I'm biased, because my entire veggie garden is done with raised beds of concrete. I think it's the most benign system you can do, and not only that, but it's fairly easy to do, and won't rot in your lifetime, or in your great grandkids' lifetimes, if you do it right.

Mine are 24" high, and only concrete on three sides, as I terraced the hillside with a cat a few years ago, so the vertical cut is the fourth side. I used slip forms, so I was able to use the same plywood over and over.

The ONLY negative thing I've ever heard about concrete (that was credible) is that it will tend to lower the pH of the soil. This has not proven to be a problem for me at all, but something to think about. Most soil around my area has low pH anyway, so maybe it's BETTER to lower it with the concrete.

I don't think you need to dig it in; I personally put hardware cloth on the bottom to keep gophers out, but now I wish I would have just put a thin layer of concrete on the bottom as well as the sides to do the job, because I think the hardware cloth will rust away before too long. If you do put concrete on the bottom, though, make sure you provide for drainage, perhaps by putting small holes in the bottom or sides.

My raised beds KICK BUTT! The plants grow very fast and very large. They also don't have any problem with blossom end rot in hot weather, they don't wilt easily (because I am able to water 24" deep) and they are great for sitting on while weeding.

Just for your edification, since you asked. Concrete is a mix of portland cement, aggregate, and water. Portland cement is nothing but ground up shale and limestone or marble which has been heated to change it from calcium carbonate to calcium oxide. There is no such thing as a "cement" sidewalk, raised bed, block, etc. They are "concrete" sidewalks, raised beds, blocks, etc. They are MADE with cement, and aggregate and water. The water has a chemical reaction with the cement. It does not "dry". In fact, it is BAD to let the concrete dry while it is setting up. In FACT, the strongest, hardest concrete you can make is poured under water!

Ready mix concrete is basically the same as any other concrete, except some ready mix comanies save money by scrimping on the amount of cement in the mix. Bad! It is also a LOT more money to use ready mix than to mix it by hand, or to bring in a concrete truck.

Hope this helps,

JOJ

-- jumpoff joe (jumpoff@echoweb.net), August 10, 2001.


I think Joe meant to say that concrete will tend to "raise" the pH - its alkaline.

-- charles (clb@dixienet.com), August 10, 2001.

We cemented a walkway around our house and it killed my two lilac bushes. My dad told me it was "lime" in the cement. I don't know if the lime part is true, but it sure killed the plants. Now, after the wall hardens, I don't know. Mary

-- Mary Fraley (kmfraley@orwell.net), August 10, 2001.

Cement works great if you have proper drainage and the pH problem can easily be solved by use of black mulch plastic as a barrier between the concrete and planting medium. Use small diameter pvc pipe, spaced uniformly, for drainage and sidewall aeration in the form, allowing it to protrude on the inside far enough to pass through the plastic mulch (this will also help hold the barrier plastic in place while filling it with planting medium).

-- Jay Blair in N. AL (jayblair678@yahoo.com), August 10, 2001.

I know that it changes your ph from the lime leaching out,, but I know alot of people that garden with that as borders, with ALOT of success. If your soil is acidic already,, then it should correct it gradually. If not,, you will have to correct forr it, with pine chipe, pine needles,,ect

-- stan (sopal@net-port.com), August 10, 2001.


To the poster with the lilacs....Your lilac bushes may have died from the roots being disturbed and then covered over with the sidewalk rather than a pH change. I've seen that kind of plant damage a lot in my line of work (forester).

Susan

-- Susan (smtroxel@socket.net), August 10, 2001.


Raise. Raise!

JOJ gettin old...

-- jumpoff joe (jumpoff@ecoweb.net), August 11, 2001.


I love my beds made out of cinder blocks, I plant herbs in the pockets.

-- kathy h (ckhart55@earthlink.net), August 11, 2001.

Fran, thanks for bringing this up! I have terrible quack grass here and it's the bane of my existence, believe me! You've given me new hope . . .

-- Jennifer L. (Northern NYS) (jlance@nospammail.com), August 11, 2001.

Very good explanation of concrete, JOJ. I want to buid some raised beds, but I'm not sure that I want them to be here when the great grandkids are gone. Can anyone give me some suggestions for what material would be best in the event I should decide to move the beds? No nasty chemicals, inexpensive, durable.

-- Jim (catchthesun@yahoo.com), August 11, 2001.


My dad has been a remodeling contractor for about 25 years. He says if you are going to use concrete, put a layer of plastic between the concrete and the dirt. Otherwise "growies just don't like concrete".

I use stone. I make my beds two feet high and the soil seems to hold the stones in place.

An alternative to concrete is tufa. It's like cement, but the aggregate is peat moss instead of gravel. Since peat has a low pH and cement has a high pH, I think the two balance out. I know that planters are often made with tufa. I know that moss grows on tufa readily.

I think stone is the best way to go because it is the most inert.

-- Paul Wheaton (paul@javaranch.com), August 11, 2001.


Last night at work, I presented your question to the agricultural researcher that is my main "guru" on things like this and as usual, he came up with a very good solution (low toxity, use of native materials and cheaper). His answer was to use agcrete. Agcrete is a mixture of 50% straw, weeds or wood chips, 25% agricultural lime, 15% mix of sand/clay and 10% portland cement. All percentages are by volume requirements. The recipe is: mix lime, clay/sand mix and portland cement. Add water to form paste. Gradually add straw, weeds, or wood chips, adding additional water to maintain a concrete- like consistancy. This mixture is similar to ancient Roman cements and has excellent durability. It can be formed and poured as concrete, but forming should be left in place longer as the curing and hardening phase takes longer than traditional concrete. Forms should be oiled or soaped on the inside to aid in removal of forms. Aggregate can also be added for additional strength where necessary by substituting stone or gravel for part of the 50% straw/weeds/woodchip component of the mix. The small percentage concentration of the portland cement used in this recipe eliminates any problem of alkili leaching into the soil and harming plants growing in and around the finished product. Also by using the clay/sand native to the area, the finished product while having the strength of concrete will resemble the surrounding ground characteristics. This can also be used as a building foundation, however, the portland cement percentage would need to be raised an additional 5% to 10% by volume.

-- Jay Blair in N. AL (jayblair678@yahoo.com), August 11, 2001.

Jay, I like your idea for using agcrete, if you live in an area where aggregate is very expensive (Bangladesh comes to mind, since there is basically no rock there. They have to bake clay to make aggregate out of pottery, basically) I suspect there are other, more local, areas which are far from aggregate sources (Like Dallas, texas, where I grew up)

But there is NO WAY that agcrete is as strong as concrete, unless you make it way thicker than concrete, and even then, its compressive strength will never be as strong as concrete.

Also, concrete only uses 16-20% cement, so the difference seems insignificant to me. Furthermore, if you've got this agcrete, filled with straw and such, won't the straw tend to rot out, leaving voids, and causing more surface area for water to contact the lime in the mix? Could well be a bigger problem, pH wise, than concrete, seems to me.

Also, how many people have you seen who grow plants along their foundations, driveways, retaining walls, sidewalks, etc? Are the plants suffering?

The ONLY problem I've had was growing an Umbrella Pine surrounded on three sides by a footing, and also on three sides by a mortar stacked rock wall. This plant turned from gorgeous, deep, shiny green to a striking deep, shiny bright YELLOW. Everyone who saw it raved on its beauty! I, of course, new that it was suffering in some way. I ended up dosing it with a handful of Rhododendron/azalea fertilizer, and it responded fairly rapidly. Within a couple of months it was showing impovement. i started dosing it monthly, and it's been looking fine for a year now.

This species is also notorious for liking acid soil. So are Rhodies and azaleas and Camelias, so that's a consideration for concrete,

On the other hand, i've got all kinds of Rhodies, and a Camelia, all right next to a concrete foundation. They are all happy as clams, and only need "normal" fertilization.

Jim, good point about maybe not wanting these things to outlast your grandkids. But I'm into bullet proof. If my grandkids don't want raised beds, they don't want a garden, with my native "soil". I guess they could just plant trees in them, or something. i'll ask them, (my grandkids, that is). I don't think they'll be too worried about it, at their age, though. :)

JOJ

JOJ

-- jumpoff joe (jumpoff@ecoweb.net), August 11, 2001.


THere was an article in either Countryside, Backwoods Home, or Back Home magazine about a guy in Arizona (I think it was, might have been New Mexico) who built a self-watering raised bed of concrete blocks. I foolishly loaned the magazine to my brother and have never seen it again. I sent off to all three mags asking if for help identifying the article. Got a letter from Countryside saying they would look for it, never heard from them again. I got a letter from Backwoods Home telling me rather curtly to look through the index on their site (I already had, couldn't get enough info from the site to tell whether they had ever published the article or not). I got the following from Back Home:

"The article to which you refer was published in BackHome's July/August 1999 issue (#41). That issue is available for $5.45 postpaid and can be ordered by mail (BackHome, P O Box 70, Hendersonville, NC 28793) or by phone with Mastercard or Visa (800-992-2546)."

I haven't checked into it further, but I'm almost POSITIVE that this couldn't be the article. I came down here in March of 1998 for a look-see visit and had the article at that time. It was published before August of 1999 (indeed, it was published prior to March of 1998), and I'm really almost positive it was in Countryside. But, I never heard back from Countryside again, so I don't know.

Maybe someone on the forum remembers this article, and which issue it was in. Maybe the same article was republished a year and a half later in Back Home, I haven't checked that out. But if anybody remembers this article and can tell me where and when it was published, I'd surely be greatful for the information. I'd like to put in some permanent raised beds one of these days myself, and had planned to implement this guy's design.

-- Sojourner (notime4@summer.spam), August 11, 2001.


I wonder "What would the straw or weed do?" The wood chip angle is similar to that cordwood construction article last issue. Thanks for putting a new question in my head. Thats what I like about these boards. Folks can lead you to a view from a different perspective so you can ask yourself "what if...". Thanks JOJ.

-- Jay Blair in N. AL (jayblair678@yahoo.com), August 11, 2001.


Jay, you are a gentleman, and a wise one. Lots of folks would have gotten argumentative. Not you. You must be ok with yourself.

JOJ

-- jumpoff joe (jumpoff@ecoweb.net), August 11, 2001.


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