Hi Steve, To address your original questions about soil heat cables.......we live in a very cold climate here in Wyoming at over 6,000' elevation with winter temps as low as -40 degrees F. We have not used soil heat cables in an outside grow box - but did decide to experiment with a grow box inside our unheated GH. We bought the cable length we needed based on the area we wanted to cover - 30" X 96" and according to the spacing the cable manufacturer recommended. We followed instructions and mounted the cable to 1/2" hardware cloth and then mounted the hardware cloth to cattle panel for extra stability and ease of moving/storing. We purchased a thermostat and set the temperature at 55 degrees F and placed the cable buried 4"s in a raised bed within our GH and made a polycarbonate cover to create a box with lids. We tried to grow salad veggies during the winter months - November thru March. The daytime temps in the GH on a sunny day were between 30-70 degrees F even when OS temps were 0 degrees F so I would raise or remove the lid during the day and cover the box at night when OS temps were as low as -30 degrees F and IS GH temps as low as around 0 degrees F. The soil heat cables were usually only running during the night so I did not notice much difference in our electricity bill. The photo below was taken on January 31st. We are in Zone 3 where danger of frost remains through June 1st and there is snow on the ground usually through April but we have had snow and frost in every month of the year during cold spells. I think most would agree the experiment was a success! The cons in my opinion is the cost of the cables, wire and thermostat and the daily covering/uncovering of the lid (although the polycarbonate only needed to be removed on sunny days because of the heat build-up). When I retire I may do this every winter but for now - it is nice to have a winter break from the GH. We also use the Soil Heat Cable as a germination mat on top of the soil in the GH in February - March as an overflow box from our inside grow lights - that works well too. We are building grow boxes this year OS for our squash and other warm weather plants and appreciate your design!

Hi. I'm trying to do the same with my mango. Since i live in central italy, i tink that growing a mango outside is out of question as much as is growing a mangosteen there where you live. I'd like to join the post to share some ideas about what i tought in the last year tempting to solve the problem. First: the soil temp. About 1-2 meters (3-6 feet) under the soil level the temperature is beginning to approach to average annual temperature of your location. This should be easy to know. Mine, for example, is 58,28F So, if you have a annual average temperature that allows mangosteen to grow (grow, not just survive) with just occasionals cold spell, there shouldn't be problems. If you don't, i guess the taproot will stop growing when it reaches the cooler soil. I'm not sure here, but i expect the roots in cold soild to be more rot sensitive, but is just a guess. You shouldn't need to heat the soil if your annual average temperature is high enough because, after a summer, the structure should keep the soil under the mangosteen hotter than the rest of soil. Second: the structure. In my city the winter are pretty long and cold (this year we got 15F, wrost winter in ten years, but not exceptional), but i manage to keep my greenhouse above 34F without additional heat just because i choosed the right spot to build it. It is attached to two concrete walls, one facing nord, the other facing east. Since, for me, cooler winds come from there it really saves a lot of heat during nights. I keep there mainly cactuses but last winter i overwintered mangoes there without any problem. For the mango now i'm building a removable cover with same ideas in mind. I have built a north wall with concrete blocks filled with dirt (to increase their termical mass and help them retain solar heat). Then i'll build the north side of the roof with some rock wool panels. The north side will have the 45 degree inclinatin to keep it close to a sphere (the sphere minimizes surface/volume ratio, thus the dispersion) and because at this inclination, at my latitude, it starts to do a shade in the structure just after 21 march, when solar heat is not needed as before. The south wall instead will be in policarbonate, will have 30 degree of inclination (at this inclination sun will be perpendicular to the panel during the cooler days, in january). The principes are the same of a water heating solar panel. To further help with it, i plan to put some drums filled with water inside that structure. During the day they absorb solar heat releasing it during nights. Water is better than rocks because has an higher termal mass. You can find a lot of ideas just googling "solar greenhouses": the idea is basically the same, the only difficult thing is to build it removable. Third: the additional heat. The idea of heating water isn't bad, you just need an acquarius heater. Surely it won't be bothered from humidity. I'm not going with it anyway, because i'm going to imagine that i'll need heat just in few specific hours: and waters takes a bit in heating and, when is heated to the point to quickly transport heat to air, takes a lot to cool down. Plus i'd like to consume as little energy as possible. I guess there are some calculation here to take, but to make it simple i have two suggestion. First idea: incadescence light bulb in series: if you put two of them one after another you'll have less light but they will put out a lot of infrared, wich is what you need. Second idea: there are some lamps just for heating chicks. No light, just heat. Put just a thermostat to turn them on when needed, and this should hopefully keep the tree heated. Just few ideas to add to the talk. I'm a total newbie, and, in the end, i do all this just for fun. I'm sorry for any mispell, english is not my laguage.

Let me get this straight. Are you saying that you can: 1) Set your heating mats (because I am too chicken to use wires) with a 'fairly fluid modified thinset Versabond', and spread a THICKER layer of thinset over the mats because you are intending to place the Ditra over the mats right away? 2) Or for the more inexperienced, is it better to do it in two steps? Put the mats down with a skim coat of thinset, level this as best as possible, and come back and apply Ditra the next day. Schluter's video for applying Ditra only, (no mats) shows the installer putting down thinset, then Ditra, and then using some type of 'wide trowel' looking device to bond the Ditra to the thinset and the floor. The thought of crawling around the floor firmly imbedding the Ditra in thinset, with delicate wire mats underneath that could be nicked at any moment, makes me very uncomfortable. It's obviously done all the time, I just find it a little scary. Any suggestions for the best procedure to accomplish this? Of course securing mats to the floor with thinset, and using that same coat of thinset to adhere the Ditra, is certainly less time consuming. Schluter's rep also said that you could lay the thinset and Ditra, and IMMEDIATELY lay more thinset and tile over the just-laid Ditra. At this point I fainted. Someone in my house eventually hung up the phone. LOL. It would seem that 'just-laid' Ditra would be "squishy" as lindalana described above and I, too, would be afraid to walk on it, let alone lay tile over it. I know, "Big Chicken." Bill, 3) I am confused over the type of thinset to use when applying the Ditra. I thought is was Unmodified. Please clarify your statement above: "For cement board, you want an unmodified thinset. For Ditra, you want it to be as modified as you can find. When I use Ditra, I'll usually use an unmodified thinset, and then for bonding it to the plywood,..." Thanks, Bill Anne

On Wed, Aug 5, 2009 at 3:43 PM, barredrock <....> wrote: [This message originated at GardenWeb] thanks for your input so far. this is what im doing now on the bathroom floor, see what you think so this is what im thinking. in this order, tell me what i am or aint doing right thanks 1. I believe it is 5/8 tongue and groove osb 2. 1/4 inch hardibacker 3. suntouch heated floor mat embedded in modified thinset and let dry how long before applying tile? 4. Do i need a leveler???? 5. ditra with unmodified thinset on both sides 6. tile ------------------------------------------ Answers Step Zero is missing. Step 1 is not enough. Step 2 is good. With expensive screws. Step 3 is good. Depends on the instructions on the bag. E.g. eighteen hours or so. Step 4 not unless you think you need it. Are these humungous tiles or puny tiles? Do you have a 6' level and what does it look like when laid on the floor in various directions? With thinset you can compensate easily up to a point.... but that all depends. Step 5 may be unnecessary, but it depends on Step 1 and Step Zero (what joists you have) Ditra is good for slabs that may crack a bit and widen horizontally. It might help also on Hardibacker or any other CBU on wood. But this has been debated a lot and never "proven" a.f.a.i.k. If your floor is springy, Ditra won't compensate enough to make it worthwhile. Step 6 what size is your tile? Have you tiled before? Do you know what slaking is? Etcetera... -- David