Question re: Heated Prop Bed Design

I have a large indoor heated bed approx. 15 feet long x 4 wide that is currently filled with about 6-8" of sand. It has the capability for misting but I am not using it yet. My intent will be to use the bed mainly for hardwood/semi/softwood cuttings of trees and shrubs.

My questions:

1. what is what is the optimum spacing for the heating cables and how deep should they be?

2. please share your opinions on covering the sand with landscape cloth (geotextile fabric) and placing flats of cuttings on that cover - is it beneficial, is it insane ... and why?

Any suggestions you can offer would be greatly appreciated!

Thank you
Michael

 

Michael--The Dept of Ag Nursery Production Factsheet gives a bit of info---generally 1 in. of sand under and 2-4 in. of sand over the cables. Common sense might dictate the spacing of cables depending on their depth...e.g. if I put 2in. of sand over a cable to "even out" the heat, I would visualize a similar zone of 2in. each side of that cable...therefore spacing them 4in. apart...make sense? At 4in. deep, I might space them 8in. apart for similar reasons. Deeper apparently gives more even heat, but they would have to run a bit more to get the same temp in the root zone, I'm imagining. I got my spacing by laying some old corrugated PVC panels down, and laying the cable in the "grooves", with some electrical staples holding the cable fairly snug in place before covering with sand. A layer of hardware cloth can be placed over the cable grid first to improve the even-ness of heat even more. Everything is about trying to avoid hot/cold spots in the rooting zone.

If feasible, I would consider laying some styroboard under this...it would be more energy efficient.

I agree with the weed fabric idea...I've run a similar little mist bed for several years and the weeds do make themselves at home in the warm, moist sand. Easy to remove the weeds, and the flats themselves do control things directly underneath, but it's always a bit of work to deal with the fringe areas where grass and cress get going.

 

Thanks for the reply!

I understand the numbers regarding spacing and it makes sense and the idea of corrugated panel under is great. Regarding cables - some of my cables have the built in thermal switch near the end. If I use them without a thermostat should the thermal switch be above the cloth or under it?

Do you have more info on the "The Dept of Ag Nursery Production Factsheet " ... I would love to get a copy from the source - is it on the web?

- Michael

 

Michael--I've never used cable with the built in thermostat...always plugged mine into a separate thermostat with a hollow copper probe that is poked into the root zone. So yours has like a little box or something containing the temp sensor/thermostat? Anyway, you want it as close to the actual root area as possible, so it will be keeping that area at the desired temp.

I got this fact sheet from the nursery specialist at the Dept of Ag in Abbotsford...for me it was a shortish drive and I wanted to pick his brains a bit anyway (this was quite a few years ago now). I would try poking around the internet and see if it's online, quite possible now. A good resource for all that stuff is

http://infobasket.gov.bc.ca/portal/...control=SetCommunity&CommunityID=300&PageID=0

Wow, that url came out awful long...if it doesn't work just try the first part and navigate to the part specializing in nursery topics.

If you have trouble, I could just fax you the 5 pages of this particular factsheet...there are other factsheets too, I believe, as well as the bigger Nursery Production Manual put out by the BC govt. Interesting reading tho dominated by info about pesticides, and you definitely have to pay for that one.

 

I also have cables with a separate thermostat but they're already in use. I will try the idea about locating the sensor nearest the root area. Regarding the link and manual - thank you very much - I will try the link and will also try to get down to CrownPublications here in Victoria to see about viweing and maybe purchasing the manual ... I am familiar with the USDA RNGR Container Nursury Manual but I am pleasantly suprised to learn of a home-grown version!!

Thank you for all your help and information!

CHeers,
Michael