Rick, I'm considering root/media warming for next Fall/Winter with an outdoor hydro system, but I only have preliminary ideas. I do know that plants respond to warming of soil, even with shortened Winter days for light. Citrus (in soil) responds, at least. I have overwintered five containerized citrus trees outside with soil warming for 5 months at this point. I used soil heating cables, with new foliage and flowering (December through April), when otherwise these citrus trees would have been relatively dormant till now. They are largely done blooming for now, as fruit has set, but there is still ongoing new foliage for 5 months, shortened days or not.

Night-time temps even in the high 30s did not prevent new foliage and blossoms on these trees, as long as soil stayed warm, but I did protect foliage with plastic sheets on the colder nights. Soil warming (with heating cables in my case), and warmth retention (with space blanket pieces and cover boards, in my case) were the critical elements to attaining plentiful Winter growth. Soil warming is a very popular topic in the Citrus forum, and I was hardly the first practitioner there this past Winter.

For warming an outdoor hydro system, which I haven't done yet, I will probably factor in a 30-gal black rain barrel reservoir sitting in full sun during day, and retaining solution warmth at night. (It will be in shade and covered this summer). I'm also thinking about using a heating cable and space blanket for warmth retention around grow modules at night. Mechanically, I very much believe successful root warming with hydro (that produces results for appropriate plants) can be achieved, even if foliage temps are much lower than root temps. I've seen it with soil, but not yet with hydro. These are my only impressions, thus far. -- Vince

Thanks Vince,

That is both interesting and encouraging.

I'm also interested in the heating cables you mention. I'll try a search in the Citrus forum. I would be thrilled if I could find a way to get nice flowering heliconias here. I can grow a couple borderline ones here, but nothing like the lobster claws and rostratas I really love.

The heating cable concept is a new one to me. Usually when I hear people talk about soil temps, it is in the context of using compost and improving soil.

Regards,

Rick Clark

To me, it's a fascinating topic, so thanks for your thoughts, thread, and response. :-) I'm very much influenced by the Citrus forum, but that flavors everything I think about from a Citrus perspective. The Citrus forum, and leaders/counselors who become quickly apparent, have pointed out that sub-tropical plants have a different foliage temp range from tropicals, and I have to research this matter for vegetables from scratch (unless someone has notes).

Soil heating cables are not even the norm over the the citrus forum. The more frequently used methods (I think) would be soil heating or propagation mats and (i kid you not), strings of small incandescent christmas tree lights wrapped around citrus soil containers. Soil temps above 64F degs are required for citrus, and above 70-something is desireable, with some growers still having success with soil temps up near 90F. Another factor is allowing the citrus roots to be below 64 degrees from November to Christmas to achieve best fruiting the next season. I was able to implement this as well, which is why my serious winter root warming did not really start till near Christmas. As you can see, even root warming becomes highly specialized, depending on the plant.

But the temp ranges and foliage tolerances for any plant in hydro would vary, and it's a research project worth pursuing (to me), with the potential for dramatic results from a sustainable approach, whatever it is.

Soil heating cables come in various types. Some can be daisy-chained, like christmas lights, some have auto-shutoff switches at various levels (mine at 74F degrees), some can be remote controlled, etc. I am *outside* of manufacturer specs with my specific cables in my specific method. (see my page for pics). this manf does not recommend using heating cables with plastic containers, and that is my specialty, at this point. LOL. Readers be advised. :-)

actually, my root temp range for citrus around Christmas was 64F to just under 68F, which was the right range for more blooms and foliage both. going over 68F meant more of one. As for veggies, I'm picking up from elsewhere that "warm season" veggies (after germination) generally need a root temp of at least 50F degrees, and beans at least 60F degs.

Consider using aquarium heaters as a means to raise the temperature of your hydo reservoir. Most have internal thermostats to keep the water temp constant. Use this guide to size the proper heater to your reservoir.

Hank, thank you for the sizing and aquarium heater info!! This is a fantastically helpful chart. appropriate aquarium heaters with automatic electronic thermostats are selling on ebay for under $5 each (prior to shipping). Given those difs between ambient and solution temps in your chart, i will probably need one 150 watt aquarium heater for the 30-gallon reservoir, possibly one soil heating cable around the grow modules or one heating mat under the modules (given they only fill/drain every 75-90 minutes), and a couple well tailored space blankets. This could be (much) easier than citrus was, actually. :-) Thanks!!

Hank, here is what I am envisioning for a circulating system, combining your aquarium heater, one soil heating cable, and space blankets. The drawing implies a system in which solution regularly circulates throughout the entire system. Just brainstorming, here. Thanks again.

{{gwi:1006055}}

p.s. the hydro system conceptualized above is actually available in two competing retail models (at least), but I left out identifying operational or design details of the non-heated hypothetical system for ambiguity. The heating angles, however, are entirely our own :-) would enjoy seeing more ideas for alternate models, and a circulating system is not mandatory for successful heating, me thinks. (will soon be gone on 3-day business trip - see everyone later).

Hello again, and happy weekend. :-) After 4+ days of thinking on this, and wanting another excuse to draw, I would just add three new graphics for hypothetical heating models. Given the goal is warmed *roots*, and given roots are often inseparable from hydro solution in many systems, the starting point for any type of hydro warming would seem to be aquarium heater(s), with space blanket wrap around system where possible. The heating cable comes into play when roots are separated from the container that houses the aquarium heater. Another factor is to ensure that containers do not rest directly on cold cement. One citrus grower (in warmed soil) this past Fall/Winter increased the temps of his citrus roots by 10F - 18F degs by doing nothing more than setting containers on 2x4 lumber. Hopefully these drawings are entertaining in some way.

{{gwi:1006056}}

{{gwi:1006057}}

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Oneweb,

Great diagrams worthy of insertion into an FAQ. Baci?

BTW what application are you using for your dwgs?

Hank

Hank, i have been using MS Photodraw 2000 (got on sale 4 years ago, and it's pretty natural to use) for all graphics above. I suppose any application that has a good "basic shapes" inventory would be very suitable to hydro freethinking. MS Paint (standard with Windows) could have produced anything I've posted thus far, but it would have taken 4 times as long. (Efficient) drawing is therapeutic for me (esp. during stressful weeks at work). Hopefully the essence of what we pursue (year-round outdoor hydro) is captured above, but four methods not yet addressed (in any graphical way) would be recovery drip, non-recovery drip, aeroponic, and passive systems. I suppose it's possible for some systems to embrace heating mats or cables without an aquarium heater, but i'm least familiar with those methods. Plus, what's the use of heating a hydro system if the solution itself isn't warm? Your aquarium heater is core genius. Thanks for feedback, and i love drawings from anyone at any time. --Vince

p.s. Let's add microsprinklers to the realm of my ignorance. and though I love drip and it's my longest-term method, it's hard to capture the essence of warming a drip or sprinkler system because there are many variables. still drawing a blank for those.....

Um...would the microsprinkler be for an irrigation system or a hydroponic application? Got a couple of ideas. :-)

I have been pondering using microsprinklers in a recovery drip-style *hydroponic* system for months, and already have much of the cheap components. But that's project 10 in a list of 30. :-) Without the heating aspect yet, the recovery miscrosprinkler drip system circuit is water pump -> 1/2" supply tubing -> 1/4" feeder lines -> microsprinklers -> media -> recovery tubing back to reservoir.

p.s. to me, microsprinkler drip is a very basic system-wide circulation model. i've already run 10 microsprinkler heads from a water pump and supply line in prelim tests. the splatter factor is yet to be tackled, when I get serious about it, but it does not seem to be a major problem given options, so hands-on testing will continue once I knock out some other things.

Microsprinkler/drip systems (*hydroponic*) become more complex for heating because (it seems to me) a grower has to tackle solution warming to start, but also additional root warming, and drip offers so many circulation and design variations that it's hard (thus far) to generalize a root warming diagram that would cover the dynamics for most drip systems.

I won't get to microsprinkler findings this summer, as it turns out. As for aquarium heaters, i just received one from ebay (99 cents plus shipping) suitable to a 30-gallon aquarium. In this case - adapted to a system with rain barrel reservoir that regularly circulates through an ebb and flow (flood/drain) system. That's the first graphic.

The instructions do not say the aquarium heater cannot lay flat. Good news. However, the fluid around the heater has to be in motion for effective distribution of warmth. Also, the manf instructions say "not for use outside the house." Once again i find myself pushing manf guidelines in flagrant but unintended fashion. Anyway, in relation to graphics above (in sequence):

1. A modular flood/drain system could probably use an aquarium heater effectively. I'm wondering if a large reservoir would circulate naturally given warm water rises (as with air).

2. A conventional tray-based ebb/flow system could likely have adequate solution circulation.

3. DWC (bucket-based) would be ideal, because it is the hydro system (pictured) most similar to a normal aquarium (air stone circulates solution).

4. NFT also seems a very strong contender for effective compatibility with aquarium heaters.

nothing more yet, but hands-on outdoor hydro warming results will have to wait until next Fall/Winter.

Please note that DO (*dissovled oxygen) levels go down as heat rises. Conceptually what you want is a multi layered media system, perhaps a coir/peat trough over an NFT bed seperated by plastic mesh (*been there done that). then you can heat the root crown, provide an air layer, and have tap root drinking it up in the NFT trough. warm root-> air layer -> cool water/nutes

Dontsleep - thanks. good points, and a "winter warming" design would likely have to take that into account. But even 8 months (or so) after this discussion was last active, and after further research and prototypes on my end...

-- I'd propose ebb-and-flow systems (flood and drain) works best in this warming discussion/application. Ebb and flow systems only fill once in awhile, typically. so .... I'd still conclude (thus far) that warming could be relevant (in a beneficial way) with ebb and flow. reduced oxygen in solution is irrelevant as solution spends most of its time drained than flooded. Hence, roots have access to air most of the time, with open access to oxygen (air) that is refreshed with every flood/drain cycle.

-- solar warming (using a large black barrel reservoir, for example) could produce several additional (night-time) hours in which plants stay warmer, but this presumes circulation of "warmed" solution around plant containers, rather than in them.

-- i recall reading from agricultural literature (for citrus in soil) that citrus trees demand more oxygen with warmer temps. perhaps this is typical of all plants? if so - that would be another check in favor of using ebb/flow, if one wants to use warming efforts.

either way, thanks for the discussion and points.

Dontsleep - your post focused mostly on media (but I also heed reduced DO with warmer temps). So for media - I think you've nailed a great concept. With coir at the top, warmth (which rises) escapes the root zone much more slowly. as coir is fine-grained, for a hydro media. So is rockwool, actually.

coir (or rockwool) on top with ebb and flow makes sense - as air is sucked down into root zone with each drain cycle. amd coarse hydroton (clay balls) under level of coir would heed your good point. so ebb and flow has another check in its favor (in context of winter warming, on solution level).

Further - with tray-style ebb and flow, the solution tray is often below the root tray, and warmth rises. warmth moves upward into root zone tray. ebb and flow scores another point (in this context).

otherwise, for other methods, how much is DO reduced if one keeps the solution in the low 70s, or perhaps even the mid 60s? These are typical temps even for roots in soil, for much of year for many gardeners.

so, I would still derive benefits of "zone pushing" of this type, given the larger factors we both presume (foliage is protected from frost, general warmth retention efforts, etc. etc.).

Thanks again. I grow outdoors all year (in SoCal Zone 9). Long story as to what i've done. My latest illustration of "zone pushing" (apart from hydro) is a bearrs lime tree, that went from 70% yellow leaves (from deliberate neglect) to 100% green leaves in a mere 10 days when I introduced "soil warming" to keep temps at 64F degrees or higher. that was soil warming - with an unconventional method (not soil heating cables - which are still relevant to hydro too, if DO is accounted for, as you say).