I woud like to plant boxwoods in large metal pots on an uncovered terrace in Zone 6b/7 to leave outside all winter. I recently heard that insulating the INSIDE of large pots with bubble wrap protects plant roots from heat and cold. Has anyone tried this? Does it work? Does the bubble wrap stay good until the plant outgrows the pot?
insulating the interior of pots with bubble wrap
I've never heard of it but you could call your local county extension agents and ask one of them about it. Good luck.
Pirl, thanks for the reply. I'll try that.
Air is the best insulator -- so yes bubble wrap is a good choice. However, you would want to make sure that drainage is still possible. A better alternative would be those styrofoam peanuts that they use for packaging. Water can drain through that and I am having a hard time seeing how water would travel through the plastic unless you punched holes through the bubble wrap. Make sure you have enough soil in there for a good root system but adding styrofoam peanuts towards the bottom and around the sides would insulate the roots and may help from freezing. It also helps with weight of the planter, it will be lighter since there will be less soil.
With a little added expense, had you thought about double potting them. A cheap pot inside. The outside pot being a little larger and decorative. In between the pots you could insulate with styrofoam or bubble wrap. Then cover the top of the plant and the insulation with a sphagnum moss or other decorative and insulating ground cover. Using the styro peanuts in the bottom would allow for drainage.
garden6-as far as how deep you would want to use the peanuts...it really just depends on how much of a root system you need for the type of plant that you will be growing. So consider how much soil you need and then fill the rest up with peanuts. Podster has a great idea too. That might even be better insulation.
I would read this thread http://davesgarden.com/forums/t/527353/ before putting too many peanuts (or anything else other than potting soil) in the bottom of containers--most of us have heard that stuff like that enhances drainage but it actually can hurt instead. If it's a huge container and the plants are small and the roots aren't going anywhere near the bottom of the container, then this won't matter, but otherwise it could. I like the idea of the pot inside the pot with bubble wrap in between--that way you get the insulation but don't end up with any watering problems.
Very interesting responses. I had been thinking of taping bubble wrap to the (inside) sides of the pots and putting a little gravel in the bottom. Maybe using 2 pots with bubble wrap around the inner one would be best. Thanks.
My take: Bubble wrap will largely be ineffective as an insulator, except marginally, as I'll explain in a second. It will only act to change the speed of soil temperature changes and have no effect on the actual low temperatures of the soil. Since it is exposure to killing low temperature that ruptures cells and kills tissue, this type of insulation is ineffective, as it does nothing to moderate potential low soil temperatures.
The exception is: If the container is near an extraneous source of heat (resting on the ground so it receives the benefit of geothermal heat) and that heat can enter the container (if you insulate the sides, the container will not be able to absorb heat through the sides, so it could only enter through an uninsulated bottom) the added insulation could have minor impact on actual low soil temperatures, but I have serious reservations that it would be anything more than very marginally effective.
My take is that it is probably "feel-good" work - lots of effort that yields less than observable results.
Al
tapla - after reading your thread mentioned above, I am not sure one would want to even bother with adding styrofoam to pots to insulate them. I am convinced by your research and comments referenced in the link. While I do stand behind the fact that air is a great insulator, I think you have proven it best to not insulate the pots and fill them up with good soil and of course a wick. =)
Oh! Thank you ms_merae, but I wasn't trying to convince you, only offer a perspective that puts a little scientific reasoning into the mix. BTW, air is an excellent insulator, particularly 'dead' (still) air. When we use things like Fiberglas insulation, we are simply wrapping something in air & using the fibers of glass to insure that it is 'dead' or not moving, which makes it extremely effective at inhibiting heat transference.
garden6. I'm chuckling at your question, but I'm a little flattered. I'm none of the things you supposed I might be, so don't let the big words fool you. Too many people overvalue what they are not and undervalue what they are. ~Malcolm S. Forbes ... just a guy who's interested in plants & has been fortunate enough to be able to retain some measure of what I read/experience, and apply it to what I see. If I'm lucky, and remain careful about interpreting what I see, the conclusions at which I arrive are occasionally usable. ;o)
Al
Tapla, your "big words" reminded me of a friend who is a geological engineer and loves gardening on a large scale. Unfortunately, he lives in SC on the marsh and that environment does not relate well to gardening in Kansas. But thanks just the same for your chuckle and the insight. Perhaps in the midst of laughter you forgot to answer the question at hand. What say you, Guy, for container planting? Or perhaps Ms_ merae gave the appropiate response? ;0)
I thought I was pretty direct in my response to the original questions in the initial post, but perhaps there are other questions I missed. Gardener2000 said Has anyone tried this? Does it work? Does the bubble wrap stay good until the plant outgrows the pot?
My direct answers would be: I'm sure someone has tried it; I believe it would be ineffective; and the parts of the bubble wrap that are not exposed to sunlight should remain usable for the life of the planting (no u.v. inhibitors in the polyethylene so photo-degradation will occur). I also think that ms_merae's response is consistent with what I might have offered in answer.
Take good care.
Al
It would be a fun experiment with a less than desirable plant and that would be destined to survive. One of those Mother Nature tricks.
I won't disagree with Taplas' right to an opinion. My response to the initial question regarding boxwoods remains the same. The only purpose to provide insulation for the plants would be a type of mulch, not necessarily to maintain an inside temperature in this case, but to block a freezing temp from doing root damage. I do understand the effect of geothermal energy on plants but this will be blocked by terrace and pot. Logic tells me to insulate the root system as best way possible from damage. This would be to avoid containers that would quickly conduct freezing temperatures to the roots (i.e. concrete) as well as provide a type of mulch. The boxwood is relatively hardy therefore root protection would be the primary protection necessary.
Three cheers for ecrane for referencing Tapla's classic thread.
I played around with some calculations this morning, assuming certain R-values for the bubble wrap, certain temperature differentials, certain soil specific heat capacities. I think that the bottom line is that even with a big container, there is too little heat stored in the small volume of a container and too little thermal resistance in the bubble wrap to make this idea useful generally.
To add to what Al said, add an external source of heat such as heat cables then it might prove useful. If we assume an R-value for the bubble wrap of 1.5, including the container, and assume that we wrap an entire 15 gallon container with bubble wrap, my calculations show that you could maintain a soil temp 14*F warmer than the outside temp using a 24watt 6 foot heating cable.
FWIW. SB
Tell me, Podster, where is the heat coming from that you are trying to retain in the container. The only likely sources are from the earth or from a heated dwelling. Insulate the container & you keep heat from a dwelling from 'entering'. If it's from the earth, you're back to what I said above. Also, you should know that there will be a half to a full zone difference in hardiness for plants that are sitting on ground as opposed to those setting on decks, railings, or in other conditions that isolate them from the soil.
How could it possibly matter if soil temperatures reach killing lows quickly (w/o insulation) or slowly (with)? What difference is there if the soil reaches killing lows over night (uninsulated) or over a 2 day cold snap (insulated)? Soil and ambient temperatures will equalize if there is no extraneous source of heat affecting soil temperatures; all that's left to ask is "How quickly?", and the question is moot. You cannot "block" freezing temperatures from doing root damage with bubble wrap, except over the very short term, which makes it ineffective for the above application.
My interest in this thread isn't in engaging someone in disagreement, but to try to prevent some unnecessary effort by some forum participants and to offer a little of the physical science behind heat transference/retention, a subject I deal with on a regular (daily) basis.
Incidentally, plants that are setting on concrete still feel the effects of geothermal heat. Of course, insulation beneath the concrete can diminish this effect when it's present, but that would be highly unusual in poured slabs. Terraces fit this aside as well. If you isolate a container from the earth's heat by setting it on a deck or railing (@ say 10* F. ambient temperature) & compare soil temperatures with a similar container that is setting on the ground or concrete, at dawn (to negate the effect of solar gain) you'll find a substantial difference in soil temperatures - maybe 10 - 15*.
If you, or others are interested in how extreme cold physiologically affects plant roots, I can explain the science behind that as well.
As I finish here, I want to add: You probably shouldn't think of this as my opinion, as it is actually proven science. Your question then, in actuality, is whether or not I've applied the science appropriately. It might not seem important on its face, but better that you focus on refuting science with science than refuting me w/o it - refuting me is way to easy and an unworthy challenge. (This last group of thoughts written tongue-in-cheek - no malice, but a fair amount of truth in it) ;o)
Best to you & any reading this.
Al
Ahh, Stressbaby - I see I was busily typing away as you were too. Thank you for the support. ;o)
Al
Well... I use broken up foamin thebottomof all of my planters..fordrainage issues.. keeping thesoil out of the drainage holes.. and the roots grow right into and through the hard white styrofoam I break up for this.. thisanchors the rootsto the soil and pots... and doesinsulate the bottoms.. from theheat on my roof top... often getting to 145*F with aday temp of 80*F. onsomeof my larger planters I line thesides with 1" or 2" sheet foam.. to insulate the plants...
None of thesewillchange the over all low temperatures in the air.. although it does slowdown the changes... this isparticularly useful to me in the lat winter... when the bright winter sun..perhaps off a snow cover... will rapidly heat up a container..thawing it out... allowing the roots to start transporting moisture up the stem.. when the freexe returns in the evening.. this upper transported moisture in the stem will freeze right away.. fractureing the cellular structure of the stem.. blistering the bark... [ usually noiticeable on the sunnyside of the trunk ] I use foam to slightly slow down this rapid thawing out.. but doesn't stop the early thawing out in the real spring... where my pots will thaw out a month or better before the ground ... this early thawing is the reason... squrrels will climb 5 floors up the fire escape... from the park on the next block.. with the peanuts they feed them there.. to burry them in my planters... so they can enjoy an early spring meal... weeks before the ones planted in the ground..
Gordon
Gordon, that's an awesome view and beautiful rooftop garden!.... Now that I read that there's a previous thread discussing all of these factors, I will take the time and become more familiar with the "science" of container soil and gardening. Thanks for the reference above so newbies like me can get "up to snuff!" ;0)