Outdoor Heating Mat Recommendations?

[Brain Treez]

I'm looking to promote root growth on some juniper cuttings over the winter, but the majority of the seedling heating pads I've found merely suggest they're water resistant and are to be used in a greenhouse or indoors. I want to leave mine out in the PNW rain. Do people just ignore the "do not immerse in water" warning with respect to getting absolutely drenched in a downpour? I know @MaciekA has described using some outdoors.

Does anyone have specific brand/model recommendations?

Thanks ahead of time for any input!

 

[JudyB]

I use these in my greenhouse which also has overhead watering that I use in there.
https://www.greenhousemegastore.com/products/redi-heat-hd-mats?_pos=1&_sid=26c52e124&_ss=r
I think you could also look at snow melting sidewalk mats, if you hook up a thermostat to any heat mat you can decide what temps the mat comes on at.

 

[actionflies]

I use the normal VIVOSUN heat mat 48"x20.75" with the waterproof electrical box to connect 3 to 4 mats outside from Amazon on collectected trees and had no issues going on 3 years of usage. I have the mats outdoor from November to April and soil temperature consistent in the 70's.

 

[hemmy]

I’ve used these Jump Start soil heating cables for early season pine repots and had good success.

I use the Bayite thermometer controller, I think I saw it originally recommended by @JudyB.

Cheers

 

[MrFancyPlants]

What sort of temp do you set the mats for?

 

[hemmy]

What sort of temp do you set the mats for?

Depends on the goal. For post-repotting pines, I want the root zone temp at 70F with the cables.

For the OP’s purpose of getting juniper cuttings growing, I’d probably run it around 60F into December and then back it down to 35-40F for 2 months and then back to 60F.

But if it’s outdoors you have to be mindful of warming from the sun and in the Midwest those occasional 70deg days in Dec or Jan.

My coldframe bed is placed in full shade for Deciduous and conifer dormancy. Which is good for dormancy, but not great for waking up pines post repot.

 

[cishepard]

Depends on the goal. For post-repotting pines, I want the root zone temp at 70F with the cables.

Do you wrap the cables around the pots/grow boxes? or lay a grid down and set the pot on top?
Do you have any photos of your setup?
I plan to do a bunch of early (Feb.) conifer repots and was going to put the trees into an unheated greenhouse for recovery, but now wondering if I should have some heat as well.

 

[hemmy]

Do you wrap the cables around the pots/grow boxes? or lay a grid down and set the pot on top?
Do you have any photos of your setup?
I plan to do a bunch of early (Feb.) conifer repots and was going to put the trees into an unheated greenhouse for recovery, but now wondering if I should have some heat as well.

Unfortunately, I can’t find any photos. I built a shallow box with 2”x6” sided and treated plywood bottom with drilled drainage holes, filled with 1” of sand and then chicken wire with the cables winding back and forth with the few inch gap between. Then another layer of chicken wire on top which is fixed to the plywood with clips. Covered with sand and mulch and surrounded with 4’ high walls of 8x8x16 blocks stacked and filled with mulch. The inside lined with 1.5 styrofoam insulation and a removable foam top. It is ridiculously heavy to clean up and move when it warms up.

According to Mirai, it is the temperature difference between the warm roots and cold foliage that stimulates better root growth post repotting. I have no idea what that mechanism is, but it seems reasonable to keep the roots warm to stimulate growth. If they are in a greenhouse, you’ll have a challenge to keep the ambient air temps from swinging back and forth with sunlight and warmer days. But you could just lay the wires out and cover them with some sand. The pots need to be nestled into the covering media, sand, pumice, Napa oil-dri, etc. it also helps to stay moist for heat conduction.

For collected trees later in the spring, I have used cables around and over the boxes, exposed to air. I do not think that worked as well.