Chinese Fringe Tree in Container?

Hey all,

I have one on order and I'm considering using it in a container - at least for a while. What is the minimum size container I should use so I can leave it outside all winter? I am zone 6b - 7 according to the new map but I prefer being conservative. Further, is there a minimum size container that would allow me to leave it wherever it is and not bring it to a more sheltered location? Thanks.

Regards,
Victor

It's a pretty hardy tree so I think it would be OK in a container, but you may need to be careful to keep the soil from freezing, and also make sure you choose a container that's not going to crack if it freezes. Obviously a larger container will help with the soil freezing issue, but you also don't want to put the tree in a container that's too big for it, the rule of thumb is when something gets a bit big for the pot it's in, you pot it up one size at a time. So as long as the tree is small, I would keep it in an appropriately sized container, and then for the winter to help protect it, you can dig a hole in the ground and sink the whole container into it and mulch over the top, then dig it up again in the spring.

Thank you ecrane. I don't get that rule of thumb however. What's the difference, as far as the tree is concerned, from being in a container that's 'too big' and being in the ground?? The ground is the biggest container around after all. Won't the tree just eventually grow into it? That's the direction I was hoping to go so I would not have to worry about freezing or moving it. I would fill in the pot with annuals while it's growing so it doesn't look too ridiculous. Thanks again.

There may be other reasons too, but one reason you don't want to overpot is it becomes much easier to accidentally overwater things when the container's too big--you want the root ball to be proportional to the size of the container, otherwise you can end up with excess water in the container that can't be absorbed by the roots, and that can lead to rot. Containers hold water differently than the ground does which is why planting in the ground doesn't cause the same problems, but I'm not enough of an expert to be able to give you a good explanation. You might want to look around on the container gardening forum--I'm sure there are probably some threads over there explaining this better, or post a question and you'll get some good answers. There's one person over there in particular (tapla) who is a real expert on how water moves in containers and he could explain this stuff much better than I can.

Thanks again. I did post it in Containers too.

Ecrane has given a pretty good explanation. One thing you might do is to keep the small tree in the appropriately sized container. Appropriate size? About where the roots can easily extend throughout the pot, say reach the side walls but without circling and becoming pot bound. It's a thin line, I know, but it's easier to figure out when you're potting up than it is to explain.

Then, if you want a larger pot for display purposes, fill it with a coarser potting mix than you used in your smaller pot, and plant the smaller pot into the bigger one.

scott

Thanks, Scott, though I still don't quite get the explanation. I just cannot be convinced that a pot would hold more water than my garden soil, which is clay. The container has drainage and would be filled with a better draining media than my native soil. Also - on the contrary, that is yet another reason for a BIGGER container - so it holds more water and is less likely to completely dry out in the Summer if I miss a watering. What am I missing??

Here's another thread where the problems with plant in too big of a container are discussed, maybe this explanation will make more sense than what I said above:
http://davesgarden.com/forums/t/685310/

And here's a great educational thread on water movement in container soils, hopefully this will help clear some things up for you too:
http://davesgarden.com/forums/t/527353/

Thanks again. I was familiar with most of the subject of the second link. I never use any material in the bottom of pots to increase drainage - it makes it worse. I tell people this and get real strange looks.

The thing is, without a plant to take up the water and transpire it into the air, the water just sits there. A pot with media mix is an entirely artificial environment. Even though there are drainage holes in a pot, water will not drain through them unless the media mix is entirely saturated. Almost as soon as the pressure of full saturation is ended (watering), drainage stops, and a saturated zone of mix remains, sometimes up to as much as the bottom half of the pot's depth. Without a plant using that water, it stays there until it evaporates from the surface--a slow process. Although drying out is a concern with containers, mix remaining too wet is a worse problem.

Scott

Thanks, Scott. Sounds like that would spell disaster for self-watering pots but I have had very good success with them - at least for annuals and some perennials. I do make sure they are also watered from the top regularly.

Victor

Back slaps all around for the container/media/moisture discussion. How about some cold water on the idea of Chionanthus retusus even surviving above ground in Stony Point, NY? Large landscape specimens of this species were killed to the snowline in 1994 here in central KY.

I'd suggest a review of the literature (at least, previous DG T&S threads on same). I believe Guy has postulated on this subject. I don't believe you can replicate the ground protection of a tree/shrub planted in your yard above ground in a container, particularly for climates that have extended periods of sub-freezing temperatures. Root hardiness only goes so far, and many/most plants are damaged or outright killed when the soil temperatures drop below the 20ºF (-6.67ºC) range.

You are all welcome to research this for yourself; American Nurseryman magazine published this type of information back in the '80s. Ilex and Buxus proved to be the most tender, dying at 28ºF (-2.22ºC). Beware buying container plants from nurseries/garden centers late in the season after exposure to sub-freezing temps, because they may already be dead.

If you have to have the Chinese fringe tree in a container, sink that container into whatever larger containerized environment you want to display it in for the growing season (providing all the drainage considerations so well outlined above). Then remove it from the larger containerized environment and sink it in the ground for the winter.

Thanks VV. I was hoping for some WARM water. Actually after I posted I realized that I was mistakenly using the native Frige Tree's hardiness in my assumption. Silly mistake. However, I was more interested in the general idea of a tree in a container and the discussion has been a good one so I did not mention that.

To keep it going though, I have seen a number of J. Maples in my area grown in large containers and left out all winter. I have had a columnar apple in a pot for years now and all I do is move it to a more sheltered area - nothing else. Also, what about wrapping the containers in bubble wrap? Surely that adds lots of insulation. Obviously the severity of the winter - specifically the duration of really frigid temps - makes all the difference and it's not worth risking something you like. I will be finding a home in the ground somewhere for my Fringe. Thanks for all the input. I'm willing to experiment with someone else's tree if anyone's interested.

Victor

I'll send you all the Ilex opaca that Kevin is unwilling to give a go in IL.

I can believe that an apple could take this type of treatment; they have much sturdier genetics. JMs on the other hand...I guess it is all in what you can afford to lose.

Bubble wrap (as well as any other insulator above ground) basically just delays the inevitable. You'd do better with your Chionanthus retusus 'Rube Goldberg' by running hot water pipes throughout the root zone. Calibrating the temperature, plants could definitely survive the winter and maybe even extend the growing season a couple zones.

I hope you have success with the Chinese fringe in a permanent spot; it's a classy plant.

Someone might want to report the correct hardiness to Plant Files--the couple examples of C. retusus that I looked at there were listed as hardy to either zone 3a or 4a (that's where my comment about it being hardy came from!) I know being in a container knocks a zone or two off the hardiness, but I figured a 3a/4a plant should make it in 6b in a container.

VV, isn't 'delaying the inevitable' the point?? That's why we wear layers in winter and not a short sleeve shirt. More insulation means it takes colder temps, or longer duration at the same temp, to have the same effect. Isn't that the same as increasing hardiness?? Again, I am not saying I will do this, I am trying to flush out the principle.

ecrane, it's not only DG. Hardiness is probably the one piece of gardening info that varies most across the many web sources. I have often found as much as a three zone difference! At least here we can correct it. Thanks.

Victor

ecrane:

DG gets errors entered just like anywhere else; it's unfortunate that this wasn't caught before now. I've checked all the standard sources I respect (Dirr, Wyman, Rehder, Bailey, Hortus III) and none give Chionanthus retusus hardiness greater than zone 5.

VG:

If you wear your layers and stand outside all winter and survive till spring, I'll toast one in your honor. If you do it with bubble wrap (and take pictures) I'll buy you a beer and/or some of Quercus' wine.

Kidding aside, all you've said is true about insulation. "Delaying the inevitable" meant delaying death only a short time. Plants in the ground have the benefit of soil temperatures moderated by the stored warmth of the earth below them (warmth not being lost to the changing/cooling air temperatures).

Sounds like time for a little test. Put a sealed bottle of water in the ground (maybe even mulch it); place one above ground; and place one above ground with insulation around it. Expose to sub-freezing temps and see when they freeze. If anyone has a good temperature gauge with a thermocouple, then regular measurements of the temperature fluctuations could even be registered.

Nurserymen overwinter their above ground stock in hoop houses where they can supply occasional heat for good reason. I don't think an above-ground container (for most residential conditions) has the capacity to retain the soil temps necessary for a questionably zone 5 hardy species in your area.

With Valentine's Day coming up, I'll keep the bubble wrap idea in mind. Seriously, there is certainly some rule of thumb regarding a plant's hardiness and survivability in a container. With perennials, my rule of thumb is at least two, preferably three zones. I have many hostas and sedum that I leave out all year. They have survived (as has the apple) two consecutive much colder than normal winters a few years back ('03 - '04 & '04 - '05). This is with no insulation or extra mulch - just moving to a more sheltered area where the house blocks the prevailing winds. I am reluctant to try with a valuable shrub or tree - hence this discussion.

Insulation can only increase the chances that these plants would survive colder temps. How much obviously depends on how cold it gets and how long it stays cold. The purpose of insulation is to slow down heat transfer, thereby moderating temperature fluctuations. So if a zone 3 plant is the safest bet without insulation, are you saying that putting insulation (who knows how much - a number of layers of the wrap?) will not bump the safest allowable plant to 4?? I doubt I would try it with a 5 in my zone 6!

With insulation, are you not stopping the transfer of heat from one environment to another? What "heat" does a container have? None. Unless you were somehow including a vast swath of ground, I can't see how insulation would help. Unless the container were ginormous, it would always be the same temp as the air(given a few minutes).

The container, and all the soil therein, has the heat that was absorbed when the temperatures were warmer! If you put a thermos bottle full of steaming hot coffee outside on a 20 degree day, are you saying it gets cold in no time? Why do we use coolers in the Summer? I fill up a cooler at 9 AM for a picnic in the summer and I am dumping out lots of ICE late in the evening. Of course insulation works, it's just a question of degree. In engineering it's affectionately known as delta T and delta t. In other words, temperature difference (between what's inside and what's outside the insulation) and the amount of time the temperature difference exists. I disagree with your last statement completely. If you took a pot from inside your house at say 70 degrees - say a three or five gallon pot - and wrapped it a number of times around with big bubble wrap - including the top and bottom (normally the top would not be wrapped, but mulched so water can penetrate but we're talking mainly about the merits of insulation here), and brought it outside, there is no way the soil temp will equal the air temp in minutes!

I've never understood the reasoning - well, actually, I do, but it's faulty reasoning - of folks thinking bubble-wrap or any other insulation material will keep an above-ground pot from freezing. If a plant were able to generate heat within the pot, maybe; but since plants don't have the capability of generating body heat, bubble wrap is just gonna delay freezing for *maybe* a few minutes, and certainly won't keep a potted plant(and its roots!) at 33F if air temp is -10F.

victorygardener, your bubble-wrapped pot brought outside from the comfort of 70 degrees to this morning's 10F outdoors wouldn't drop to 10F within *minutes* - but it would be there within a couple of hours, and from that point on, it would be at whatever the ambient air temperature is, from now 'til the end of time.

I never said insulation would keep a pot from freezing - not sure where you got that from. And no, the temperature of the soil would certainly NOT be the same as the ambient temperature 'til the end of time' if it did in fact get down to it in a couple of hours, or however long. Insulation moderates fluctuations in tempeature, it does not 'lock in' a certain temperature. In fact, if the pot got down to 20 or whatever cold ambient temperature existed, and the ambient temp then rose rather quickly, the temperature of the pot would be LESS than the ambient for some time. It works both ways.

The concept here is how much insulation (if I were to actually try this I would use bubble wrap and foil wrap, which works as a radiated heat reflector) acts to delay the drop in temperature until the air is heating up once again - hopefully the next day. The magic number here is not 32 degrees, but the temperature that causes permanent damage, as VV was referring to. As I said, I have zone 4 plants left outside with no protection, other than from the wind, which certainly see temps well below freezing and come back every year.

There seems to be an odd understanding that insulation does absolutely nothing. Why are row covers used when there is a threat of frost?

Row covers keep heat from the ground in.

And insulation would keep heat from the pot in.

We used to bank a regular water hydrant with horse manure/straw and it kept open pretty much all winter just outside Naperville IL. This was back in the early 40's when winter in "the land of Lincoln" had some nip to it.

Too add some fuel to the fire...

Why do you have to keep the tree outside all winter? Can you toss it into a garage or shed? That is what I do with my japanese maples that are not in the ground yet . My unheated garage provides just enough protection for these maples provided they are in a large enough pot.

http://davesgarden.com/forums/fp.php?pid=2989894

Let my thrashing begin.

Willis

Hi Willis,

I don't have to! I was merely considering it as an option when I believed the hardiness was better and I wan't sure about where in the ground to put it. I am converting my house to solar, had to take my primary shade tree down (Norway Maple - no great loss, except for the shade) and have limited space. If I knew for sure what I will do with the area that used to be under the Maple and is now in full-blown sun, I would most likely plant it there somewhere - close enough to the house to enjoy the fragrance and it should stay small enough not to shade the panels. However, I am considering decking the entire area and erecting a pergola to provide the lost shade. So that's where it started. I would not even think of attempting it with a zone 5 quality plant but the discussion evolved (or disintegrated, depending on your viewpoint) into the merits in general.

Victor