Sawdust for my medium

oakleaf33(8)August 24, 2008

Hopefully grizzman will come across this sometime this week. Im about to break ground in about a month or so on my new commercial tomatoe greenhouse. I should have this problem figured out already. I plan on using sawdust in the 3" sewer pvc for my growing medium. I work at a cabinet shop where we have sawdust like you cannot fathom. Would it be a bad idea to use it or not. I can get all I want of it free by the truck loads. I think it's organic, what am I talking about of course it is it comes from trees..Anyway anythoughts

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greystoke(South Africa(11))

Don't use it on its own. It compacts very badly, and it also goes acid.
I've used it succesfully mixed with river sand, peasized gravel and perlite.
Woodchips work better.

    Bookmark   August 25, 2008 at 12:12AM
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Hey oakleaf, get yourself a copy of Howard M. Resh's book "Hydroponic Food Production". I think it's absolutely vital for anyone looking at commercial scale hydroponics, and I recommended for hobbyists as well.

With Sawdust Culture you have to make sure to steam or chemically sterilize the sawdust first and between each crop (if it's re-used). There is usually a problematic sodium chloride content in most wood, requiring pre-leaching.

There's a whole chapter on it in the book (chapter 9). The salt content of wood is especially important to check on because many logs are floated in seawater for a very long time on their way to the mill, meaning they absorb a lot of salt.

Oh, and you can't use Western Red Cedar - it's toxic.

Douglas Fir and Western Hemlock make the best sawdust for hydroponics.

    Bookmark   September 4, 2008 at 9:17PM
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Good grief I thought was good at this stuff. You guys are like unblievable when it comes to know the most strange sounding but vitally important. I mean I get it and know a lot of stuff but never would have seen the sodium chloride thing. Oh yeah thanx for the book recommendation. I will definately make it my next amazon purchase. I'll get back with you guys

    Bookmark   September 5, 2008 at 10:32PM
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freemangreens(Zone 10 CA)

Do your homework and you'll realize you don't NEED a growing medium for anything except to hold the silly plants until they can hold themselves, right?

Just to be fair, I use washed river sand for some of my stuff and rock wool for others. I grow everything from heirloom seed.

River sand is inert and almost free. It is reusable and if you use your noodle, won't get back to pumps (hint: elevate the pump in the sump!)

For 90% of my stuff, I start things in sand, then transplant to a different system when the plants are a few inches tall. Sand washes off 100% with just a dip or two.

God bless.


    Bookmark   September 9, 2008 at 1:14AM
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Yeah, the growing mediums aren't absolutely required, but they are a lot easier to deal with for many plants. The less support you get from the medium the more support you have to give the plant some other way.

Even if all you do is put a plant in a little 2" net cup with some hydroton and it grows into a 6 foot monster tomato plant, you've got a decent amount of crown support you can tap into. Media-less growing (aeroponics) is definitely possible and advantageous in certain applications, but it is also more temperamental (compared to media with water-retention and/or cation exchange capabilities), requires better technical planning, and generally is just less forgiving of mistakes.

I'd have to say that if no mistakes are made in comparable systems with the only variable being hydroponics versus aeroponics you'll probably see a bit better cost effectiveness in the aero, but the potential for loss and increased labor are a risk. In commercial applications it is far more common to see standard hydroponic systems in use.

Oh and oakleaf - I'd say at least half of what I know is still "book knowledge". I just have a brain like a sponge so I absorb it all very easily and can spit it back out. I haven't tried a lot of the stuff I know because, well, I don't have nearly enough room to do it and I'm not nearly rich enough to throw around that kind of money.

Getting into a greenhouse and doing it on the scale you're planning is infinitely better training than reading an entire library. I know I've learned more truly valuable knowledge with my hobby set-up in the basement than I did from the books, but neither is really useful without the other.

Before I did it with my own hands the knowledge wasn't "real", and trying to do it without the book learning would've been silly. You've got a good foundation and your practical work is going to build on that a hundredfold.

    Bookmark   September 11, 2008 at 3:36AM
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