I live in a marginal zone between zones 6b and 7a depending on the year. On the description of the plant is says that it is only hardy to zone 7b. I was wondering if I could have it overwinter outside with minimal protection? It would be placed in a raised bed surrounded by large basalt boulders and up against a concrete wall facing south. The soil is very sandy and my winters are relatively dry except for a few snow falls that don't normally stay for very long. If I were to protect it I think that making a "box" around it with wood then, wrapping that in clear plastic would be sufficient. Any advice would be good.
I very much doubt that the plant would be hardy for you. A pdf from the University of Florida (IFAS) is very cautious http://hort.ifas.ufl.edu/shrubs/AGAAMEA.PDF Some of the yuccas and their allies might thrive. This afternoon at the annual Leu Gardens plant sale in Orlando, I got a recommendation to check out http://www.yuccado.com/, a Texas nursery with plants like Agave gracilipes, which at least gets into the correct zone range. I'm not in touch with agave, yucca, or nolina enthusiasts (there seem to be plenty in the western states).
Where in WA? Your USDA zone doesn't change annually, it's based on an average of low temperatures taken over a period of years. It doesn't bounce up and down with short-term variations in minimum temperatures. Some overwintering of these outdoors is accomplished in western WA (where the lowlands are USDA 8) but fully developed, flowering plants are a routine feature only in places like southern Calfornia and Hawaii. However, there are smaller-growing species that are much hardier, and as mentioned other kinds of hardy plants with evergreen rosettes. Check out (Ian Barclay's) Desert Northwest web pages if not already familiar with this resource.
Many so-called, cold-hardy, succulent plants can tolerate lower temperatures than what their zone recommendations would indicate. However, it is imperative that it be a dry cold. For example, you will find that sometimes specialty nurseries will sell certain cold-hardy Agaves to the western US, but not to the eastern US, even though the zone number may be the same. The winter we are experiencing in Michigan right now is one that will kill most cold-hardy succulents because we are having repeated cycles of rain and snow. When it is warm enough to rain succulents will take up water, then when it freezes, it causes ice crystals to form in the cells, killing the plant. What should happen is that most cold-hardy/alpine succulents will dehydrate themselves before the cold sets in, reducing the risk of cellular damage. Protecting these plants from the cyclic rain and snow is important. As you know Agave americana can grow to be a very large plant. That said, trying to protect the plant from cold, wet conditions will be progressively more difficult as the plant grows. I love succulent plants because of their general resistance to many pest and diseases...provided proper soil/drainage conditions. Some I have to bring indoors for the winter, some I can leave outdoors protected from the snow. The trick is carefully choosing plants that can be portable in their containers so that they can be moved to a protected winter location. I have a hand-truck that I use to move my larger plants. This link will give you an idea of the types of Agaves that may be better suited for your climate. These are all zone 6 cacti & succulents appropriate for the western US. http://www.highcountrygardens.com/c...egions=801,802,803,804,805,0&zone=6&x=31&y=16
Ron B, When I said "I live in a marginal zone between zones 6b and 7a depending on the year." What I meant was that my region, east of the cascade mountains, is listed as hardiness zone 7. However, just this last winter we had a week or so of lows to -3 F and highs of 10-20 F ,that is zone 6 weather. Some years are closer to zone 7 than zone 6, that is why I said I was in a marginal zone between 6-7. We normally do not get down into the negatives for any amount of time and it is always fairly dry in the winters. I thought that because it doesn't get very wet here to rot the plant that I could build a sort of shelter from wood and wrap the "box with clear plastic and protect it that way. Does anyone have any thoughts on this idea or am I overstepping my zone boundary too far.
My point is the way they arrive at the USDA zones there is no such thing as a Zone _ winter. It's based on averages over a period of years. A place may have winters with temperatures below the representative range some years and above during others, the range is where the average annual minimum temperature falls and is not the range of record lows for that zone. Awhile back there was a story somewhere about a guy in Yakima who got a century plant to flower in his garden. It was planted on the edge of a droughty ridge or terrace and covered each winter to exclude hard frost.
People have been doing greenhouse tricks for years. Orangeries, covers for veggies, cellars to store dormant roots... Some sort of winter shelter for an agave ought to be workable. That south-facing concrete wall should be quite useful. A famous southern magnolia tree in Brooklyn prospered due to being in front of a south-facing house. Still (assuming you're west of the Cascades), how about a charismatic Nolina or something of the sort?
>my region, east of the cascade mountains< Speaking of southern magnolia some friends and I once noticed a quite nice form with dark indumentum etc. in an eastern WA back yard. The owner gave us the incredible planting date of something like 1948! But perhaps the most out-of-its-natural realm specimen I have seen personally was one growing in a planter against a wall of the Mormon Temple in Salt Lake City.
South side of the Temple sounds comfy. Apparently the Great Salt Lake buffers Salt Lake City's climate-they may be zone 7, the same as Washington D.C. (where magnolias grow happily on the White House lawn). In the midst of their native range--in places like Jacksonville, Fla., they are rather fast growing and specialize in growing straight up in forests, eventually reaching full sun. The result is tall trees with straight trunks. Unfortunately, magnolias are sort of short-lived in yards. People get tired of cleaning up the leaves and the "cones". Not to mention the near-surface roots and the deep shade, which discourages the all-important grass.
Sunset has Great Salt Lake zoned in Sunset Climate Zone 3a: Winter minimum temperatures average from 15 to 25F (-9 to -4C), with extremes between -8 and -18F (-22 and -28C) No other southern magnolias were spotted in the region on that trip. This has been called one of the world's most popular trees, usually if an area is considered suitable multiple planted individuals of this species are seen.
I've had three survive on a 14th floor terrace in New York (6a or b, depending on all sorts of things), planted in terra cotta pots about 18" in diameter. It is a south- eastern site, protected from wind, and very sunny. They look pretty awful in the winter but have come back now for three years and counting.
