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February has given us almost “normal” weather this year – consistently cold (although never extreme), and a bit of precipitation (although not as much as we could use). The first of the spring bulbs (Iris danfordiae and other reticulata irises) are coming into bloom now, a few weeks later than in previous years. Outdoors, I’ve prepared the area for the blue grama grass restoration, and burned some weeds and clutter from last year to clean out some areas.
I’m trying something new with the hardy perennial seeds I received from the NARGS seed exchange or purchased locally at Plants of the Southwest. These enjoy a period of cold treatment to stimulate them to germinate in the spring, so I’ve planted them in plastic inserts and set them in an open, unheated cold frame outside. Curious to see if this treatment suits them.
Indoors, seedlings of vegetables, herbs, flowers, succulents and hardy cacti are thriving under the grow lights. A few of the cactus and succulents have not germinated. Perhaps they are waiting for warmer nights?
I’ve noticed just this week that the one- and three-year-old cacti that I’m growing inside are starting their spring growth spurt, getting a little plumper and greener. I’ll resume watering them weekly now.
My new Meyer lemon tree was attacked by gray aphids. A vigorous hosing off outside seems to have addressed the problem, at least for the time being.
Winter is a good time to enjoy some garden reading. I’ve been on an iris history binge this month, working through the American Iris Society bulletins from the 1920s, which are available on line to e-members. I’ve also had the good fortune to acquire a complete set of publications of the Dwarf Iris Society, and have been reading Walter Welch’s DIS portfolios from the 1950s.
It’s mid-December now. We’ve actually gotten a bit of snow, providing the garden with some welcome moisture. There’s nothing blooming or even very green any more, after temperatures dropped down into the low teens earlier in the month. Some of the plants add a little bit of “structural” interest, however, such as the red-twig dogwood and a gone-to-seed parsley plant I left standing.
I did some clean-up last weekend, burning two enormous piles of dry weeds (mostly tumbleweeds and chenopods).
My cactus and succulent seed orders have arrived, and the NARGS seed exchange opened earlier today. I found a few irises there that I can use, so put in an order and filled it out with “surprise me” requests in my favorite genera.
Seed catalogs have been arriving, and some of those I haven’t received yet have their 2013 offerings on their web sites. So now I’m planning in earnest for next year, going through the seed inventory I have left from last year, and deciding what new things to try.
While reading Laura Springer Ogden’s The Undaunted Garden, I became inspired to restore a section of the backyard with native blue grama grass. It was once the dominant vegetation in this locality, before farming and overgrazing took their toll. I’m hoping that it will eventually supplant the unpleasant weeds and lend a natural look to the space. I’m planning on underplanting with spring-flowering bulbs for extra color and fun. I’ll post on this project as it goes along next year.
Here’s my second excursion into the world of video. This time, I’m planting seeds I received from the seed exchange of SIGNA, the Species Iris Group of North America. I share my method of starting seeds of plants (like irises) that require a period of cold stratification in order to germinate. Enjoy!
Anyone who becomes interested in perennials quickly encounters the USDA hardiness zone map, which is ubiquitous in books, catalogs, and nurseries. The idea is that the minimum winter temperature in a given location can be used to select plants that will survive most winters. Of course, there are usually some caveats given about snow cover, microclimates, and so on. And not all nurseries list the same zone rating for each plant. I’ve seen a couple that seem to rate anything they don’t know about as zone 9!
People apparently take this system very much to heart. It may be the only information a catalog gives to indicate the plant’s requirements – it’s obviously regarded as a terribly essential datum. Perhaps it’s our love affair with numbers, or the sense of security that comes from “knowing” which plants will survive and which ones won’t. Experienced gardeners, of course, know that you can lose some plants rated for a colder zone and successfully overwinter some rated for a warmer zone. I started wondering how useful these hardiness zone ratings really are. How well does the zone rating actually predict survival?
Last year we had one of our coldest winters on record. The temperature dropped to -18 Fahrenheit at the beginning of February (with no snow cover), and the lows stayed below zero for a number of days afterwards. This is about the lower limit of hardiness zone 5. A simplistic interpretation of the hardiness zone ratings would imply that most plants rated for zone 5 or lower would survive, and that those rated for zone 6 or higher would perish.
What really happened? Well, I made note of how many of each particular plant survived in my garden: 0 if none survived, 1 if all survived, and, for example, 0.5 if half of them survived. I also used a 0.5 if the plant survived, but was so damaged that it was effectively set back a year in growth. I then plotted this “survival rate” for each plant against its hardiness zone rating. (It’s a limited amount of data, but I intend to add to it each year.) The result is interesting:
The best-fit line running through the graph demonstrates that there is in fact a trend in the expected direction: higher zone ratings correlate with reduced survival. But the scatter of the points themselves makes an even stronger point: for any given plant, the hardiness zone rate is a very unreliable predictor of survivability. There were zone 2 and 3 plants that fared no better than the zone 7 plant!
In William Cullina’s excellent book Understanding Perennials, there is an explanation of the mechanisms that plants use to survive freezing temperatures. Truly tender plants (think of tomatoes or basil) simply cannot survive prolonged temperatures below freezing, because the water in their cells turns to ice and expands and destroys the cells. Some plants have chemicals in their cytoplasm that act like antifreeze and prevent freezing, even down to temperatures as low as 20 degrees. But to survive colder temperatures than that, the antifreeze strategy alone is inadequate. At lower temperatures, the cells will freeze, and the plant needs specially designed cells that can freeze without being destroyed (by shriveling to make room for the ice crystals, or by having particularly tough cell walls). If a plant can survive losing its top growth, that is also helpful, because the soil temperatures do not swing as low as air temperatures, particularly under an insulating cover of snow.
Cullina also describes how the timing of cold weather can effect hardiness. No plant is fully hardy when in active growth. Plants must prepare for cold weather in the fall and then return to growth in the spring. If the timing isn’t right, the plant can die from an autumn or spring cold snap, even if it could survive much lower temperatures in mid-winter.
The upshot of all this, in my view, is that the concept of hardiness zones gives a completely unwarranted false precision to a matter that is really pretty hard to quantify. Especially when we start talking about zone 5a or 5b, it seems like what some of us in the sciences refer to as “sharpening the marshmallow”. I think gardeners might be better served by a much loser set of terms, such as “tender”, “semi-hardy”, “hardy”, and “extremely hardy”. About the only solid advice I’m inclined to give people about selecting perennials is “If you live where it’s below freezing a lot in the winter, it’s probably a waste of time to try anything rated for zone 8 or higher.”
Mostly, we just have to live with the fact that we don’t know what will survive any given winter.
Mid-winter is a philosophical, almost mystical time, for a gardener in a temporate climate. Casual gardeners no doubt forget about gardening entirely at this time of year. Our local nurseries all close from Christmas to New Years – presumably because hardly anyone would show up if they stayed open.
For the plants in the garden, this is essentially a dormant time. They wait in quiet slumber for spring to come, completing the cycle of activity and rest that is common to all living things. This is the time that connects the end of one growing season with the beginning of the next, completing the circle. I might use this space to write about all the fascinating things that plants do in winter, away from our active notice. But instead I’ll share some thoughts on two different ways a garden can move from year to year.
The first way might be called “reinvention”. In this model, trees, shrubs, and perennials are expected to survive the winter and maintain the basic framework of the garden. Annual flowers and vegetables die at the end of the season and are replaced anew from seed the following spring. If the garden is relatively new, we may acquire new perennials and trees as well. We may even cycle through perennials every few years, as the allure of new plants compels us to send the current residents on their way to free up space.
Starting over each spring is truly a great deal of fun. Since I was a teen, I looked forward to the arrival of the garden catalogs in January, and the long hours of temptation and anticipation they provided. There’s always a new tomato to grow, an new iris to collect, a new batch of violas to be set out. When I was young, this was what a gardener’s winter was about!
The second way of bridging the seasons might be called “recycling”. In this way of doing things, most (if not all) of next year’s plants come directly from last year’s garden, either perennials that we have kept going, or annuals and vegetables raised from last year’s seed. We can let desirable plants reseed in place, or – if more care is needed – harvest and save seed for replanting next year.
Recycling your garden reinforces a mindset of sustainability, taking us back to a time when there were no new plants or exotic seeds from far away to provide garden novelty each year. Recycling your garden can offer an alternative to the increasingly commercialized garden industry, which is threatening the biodiversity of our food crops by narrowing the once enormous range of local heirloom varieties down to a small assortment of hybrids obtainable only as new seed each year from commercial sources. I recommend gardeners all acquaint themselves with organizations like the Seed Savers Exchange that are working hard to preserve heirloom flowers and vegetables.
I’ve made a conscious choice to move more toward a recycling garden each year. I’m starting to save vegetable seeds, to encourage ornamentals that reseed themselves, and to explore perennial vegetables, such as asparagus and walking onions. I like the change in mindset involved: the plants in my garden become less disposable commodities, and more like long-term resources.
That said, I think there will always be a place for reinvention in my garden. Gardening is my hobby after all, and it would lose some of its interest if there were no exploration of new plants. Furthermore, my garden is still a new one, and experimenting with new plants seems altogether reasonable when new ground is brought into cultivation. Still, I cannot but reflect that the “reinvention” paradigm has led many a gardener down a perilous path where the need for acquiring novelty outstrips the space, time, and money available. I’d like, in a few years’ time, to reach a state where the garden I loved the year before returns from its own roots and seeds in spring, and changes are modest and measured.