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Discussion in 'Outdoor Gardening in the Pacific Northwest' started by Ron B, Dec 1, 2005.
Grevilleas on ground, bamboo and one embothrium reaching for it. Guess it was waiting for December.
Hmmm, I have to stay on top of those plants that don't seem adapted to snow that well. In very few cases does snow do any harm, since it's actually insulating stuff compared to exposing leaves to clear cold dry conditions in winter.
My little embothrium also bent right to the ground, bet it's doing it again this morning...hope it can bend back once it's dusted off! Didn't know grevilleas had a problem with snow, but makes sense...they don't see much of it down under.
I'm trying to leave the snow on my echium piniana since they are so sensitive to the cold, but it's quite tall and already leaning over like they often do...what to do, other than moving to California!
>hope it can bend back once it's dusted off<
C-r-r-r-e-e-e-e-a-a-k! Mine is on the way back up but I'm not sure it's going to make it all the way. It's the form with lobed leaves (at least when small) collected and sold by Heronswood nursery, Kingston, WA. I'm also having some serious leaning on 'Inca Flame', imported from Duncan & Davies nursery, New Zealand and purchased from Herb Senft, Sequim, WA (not remembering name of his nursery at the moment). But it is being crowded by the western redcedar that was supposed to form a backdrop, so it's not being deformed by this recent snow only.
How much of the stuff?
Had about 4 or 5mm here on Monday, which lasted for about 2 hours before it thawed. The weathermen had been predicting all sorts of doom and gloom over the previous few days, that the whole country would be paralysed, etc, etc, etc.
I thought the whole country was paralyzed already. Bwa-ha-ha! Anyway, looking out the window at what's left today I'd say there was at least 5 cm (2 in), maybe more. Certain plants went right over, most others did not.
I find it interesting just how much the snow accumulation varies by neighbourhood here in Vancouver. At my home in Kitsilano (very near sea level) there is very little accumulation. Five kilometres away at UBC there is a thick blanket of snow, maybe 3-4 cm. UBC is around 100 m above sea level. You really have to consider the microclimate when planning a garden in a city with so many hills, slopes and water.
Same pattern reported from Seattle, with hilltops and more northerly neighborhoods getting some, lower areas getting none.
My Persea was knelt in prayer through the night. It spontaneously grew in the compost heap and survived the last two winters there. I potted it up this year and hope that it makes it. Is it really true that one should consider a potted plant experiencing over 25 degrees Fahrenheit colder temperatures than a plant in the ground is experiencing? Salvia dorsiana has survived the last two winters in a pot, but she has not been happy this week.
Arboretum, Seattle, Zone 8, dusk yesterday;
Garden Shed, foothills of the Sawtooths, Idaho, Zone 4, midnight last night.
Roots less hardy than tops. Immature roots less hardy than mature roots. Part of root system of unprotected potted plant may freeze while top still looks "fine" afterward, erroneous conclusion is reached that plant was unaffected by cold exposure. Broadleaf evergreens seem to be considered most vulnerable by nurseries. Immature roots of Buxus sempervirens have been seen to die in one study at 26.6F/-3C, those of Cotoneaster microphyllus perished at 24.8F/-4C, and Ilex cornuta 'Dazzler' lost them at 24.8F/-4C. Mahonia bealei and Pyracantha coccinea 'Lalandei' same as the holly. However, immature roots of some deciduous plants are also rather tender. Magnolia x soulangeana has been found to lose them at 23F/-5C, likewise for M. stellata. See Whitcomb, Establishment and Maintenance of Landscape Plants.
Moisture levels in containers is another factor that has been little researched.
A researcher at Corvallis mentioned to me that they have been able to overwinter most common plants without any protection as long as they are sitting on drained capillary sand beds. His suspicion was that eliminating the perched water table in containers significantly increased the root hardiness, as most root damage (to otherwise "hardy" plants in one's zone) results from free water forming ice that slices/dices the root systems. This explains why (hardier) plants can have their root systems frozen solid in the ground, and have no damage, but the same freezing solid in a container will badly damage or even kill them.
Root hardiness tables that are available are based on containers under normal growing conditions (not on these sandbeds, which eliminate the saturated zones in the bottom of containers).
My understanding was that this is a different factor than the actual freezing of tissues that harms less hardy plants.
Searching "capillary sand beds" on www to find out what this involves I read that in an Irish experiment "Eight of the beds were capillary sand beds in which the bed was filled with a non-calcareous sand and a constant water level maintained in the sand, 2 cm below the surface, by means of a float valve. The pots containing the plants were placed on the moist sand and obtained water through capillary action."
How does this improve drainage within the pot? There's a continuous connection between the water inside the pot and out, so water draining through the soil column inside the pot doesn't back up at the bottom of the pot and form a perched water table?
Ron--you're correct. The sandbed under a pot extends the water column, so the saturated zone occurs in the sand bed rather than the pot.
In winter, the bed can be totally drained so that the excess moisture drains even more readily from the container media. You could also approximate this by setting pots onto bare sandy soil, making sure it contacts the drain holes...this can wick away the perched water table in a similar way, assuming that the soil is well drained.
Corvallis was doing work on these sandbeds, resulting in a couple articles in American Nurseryman several years back. They have been used for years in the UK and New Zealand, haven't caught on much in more continental climates.
The second part I don't get: once the connection is broken with the water in the bed, the water draining from the pot should go back to not draining from the container until field capacity is reached. It shouldn't matter if the pot is sitting on a coarse material like sand or not.
Correct again Ron. You make me think, thank you!
Pots on my sandbed here will always have a capillary connection thru the winter, because they are exposed to almost daily rain thru the winter. The sand layer remains evenly moist, (it's about 3-4 in. deep) except maybe during an arctic outflow that could dry it out somewhat. But under those conditions the container mix would also be drying out, and not have any perched water.
If somehow the sand did dry out much more than the media in the containers, the water column could be interrupted, same as it always is when containers are placed on gravel covered beds. Then if the container was watered, say with a drip emitter, the water might saturate the bottom of the container and not move into the dry sand below. Rain (or overhead sprinklers) would immediately reestablish the capillary column, and remove any perched water.
This doesn't happen here or in the UK climate. Maybe in continental areas, with little winter rain, the beds would be kept irrigated as in summer. Here, setting the water level very low (drained) just helps make sure there is never water building up in the sand, say if the rain gets real heavy.
Apologies to all those who don't want to follow this topic...I haven't found many folks in the past 2 years who did. I just like to tinker with alternative stuff...
Your posts caught my attention because I am a garden centre owner who is trying to look at less labour intensive methods of maintaining nursery stock. I have seen a few references to sand beds lined with plastic used in growing operations but nothing about use for maintenance of stock - our whole goal is to keep it looking as good as when we got it until the customer buys it. Our garden centre is in the Ottawa area. We have generally been nearly 100% successful in overwintering in containers but last year's repeated freeze thaw created an ice layer that was slow to melt with a cool spring and rotted the roots on a few hundred shrubs - viburnums especially. The idea of overwintering on sand beds is attractive if it can decrease the chances of spring root rot. I would appreciate your input on this subject as I will have to decide to trial sand beds in our 'overstock' area or in the main retail area - we would overwinter the plants in 'overstock' and it would have the added advantage of decreasing the water schedule for the area least looked after! Sand beds in the retail area would give me accurate data of the time saved as we already know how much labour it takes to water the retail area and mean number of plants in the area is consistent for most of the selling season (May to October). Thanks alot!
Doug--I have heard of a retailer in the U.S. Midwest who tried then abandoned the capillary idea in his retail sales area. I recall he found the variety of potting mixes gave spotty results (typically the media has to be heavier than the normal very bark dominated mixes used under overhead irrigation). Another problem would be the need for drain holes on the bottom of a container...side holes would give very limited contact with the sand bed.
Otherwise, I do understand that there is quite a labour investment in keeping the retail areas watered properly, and the plants I see at garden centres often show the failure of staff to accomplish this.
Overwintering is another question...the cold must be a problem for you as well as the moisture problem. Here the wet is more trouble than cold for many plants. Would you normally overwinter most things in hoophouses...in which moisture could be quite well controlled?
Well, failure of management anyway. I think much stock left sitting out here is also damaged - I know I have bought plants left out and discovered later the small roots were dead - but since the tops don't brown it's thought they were successfully overwintered without protection. Killing temperatures for small (immature) roots are quite high, relative to the hardiness of the top.
Except where obviously recently potted, apt to fall apart I knock small plants out of pots and inspect roots before purchasing--when I have the chance.
The capillary action you are speaking of is called gravity. the holes on the BOTTOM of the pot need sand to sit on because otherwise they would be sitting on a flat solid surface and the holes would be blocked and the water would have no where to go; so of course, lacking drainage, the pot will saturate and form a block of ice.
Roots are not resistant to freeze according to age either. They are resistant dependent upon species and food fed; kelp and such can help prevent frost damage to fruit trees down to 28F sometimes due to the high density of the minerals that certain ferts contain.
The flux of temperature is what usually kills the plant. If you avoid the sudden thaw and thaw at slower rates instead, then you have no frost damage. try it. When your tomatoes freeze, then go out before the sun comes up and foliar them with cold water to melt the ice and the plant does not suffer frost bite. It is also the way they warm people suffering from frost bite, they do it slowly to avoid tissue damage.