I was just reading Graham Rice’s musings on plants that grow in the coldest climates. He observed that the resources he consulted did not agree on which plants were tough enough to take USDA zone 2. If you’ve been gardening for any length of time (which of course Graham has), this won’t surprise you.

First, there is the matter of statistics. The fewer people gardening in a certain zone, the less data available on any particular plant. I imagine with a lot of plants, to say it’s hardy to zone 2 is as much an educated guess as it is a tested hypothesis.

And then there are so many factors affecting plant hardiness besides air temperature that some people think the whole concept of hardiness zones is a joke. Ellen Hornig of Seneca Hill Perennials admits, “We include hardiness zones largely to pander to popular prejudice and give you a small degree of guidance.” Tony Avent provides a detailed analysis of the problems inherent in the concept of hardiness zones.

But you’ve got to start somewhere. That’s where other local gardeners are a tremendous help. If anyone is going to know what will make it in your garden, it’s someone with the same growing conditions. And many people who are still too isolated to find a local garden buddy now have the benefit of internet access, and can consult and befriend others in similar conditions.

This caryopteris was a gamble that I lost. It failed to return after its first winter.

On the other hand, I suppose you might kill more, because you may become more willing to take chances. I find my willingness to experiment is constrained by the limits of my pocketbook. I will try a perennial rated a zone or even two zones warmer if I think I can provide the other conditions it needs, perhaps shade and moist, acid soil. But I am more conservative when it comes to an expensive tree that requires a lot of digging to plant–and to dig out again when it dies. Gardeners with a bigger acquisitions budget will be braver. Wayne Winterrowd and Joe Eck, in A Year at North Hill: Four Seasons in a Vermont Garden, describe many rhododendrons in their garden that aren’t considered hardy in their zone. But there they are, grown to maturity. Winterrowd and Eck were not assured of success when they planted them.

Graham Rice has a tough job, writing about plants for an area in which he’s never gardened. I imagine after consulting reference works, he’ll talk to friends and colleagues more familiar with gardening in that rigorous climate, and maybe seek out a gardening blog or two. Northscaping, which I’ve mentioned before, is another good source of hands-on cold climate gardening information.

Seeds waiting to be sorted

It’s even better when you can find a seed company that specializes in seeds for cold climates. Recently, a reader asked me just that:

I live in Norway long term and am trying to find cold climate food seed for my garden.

On my Cold Climate Merchants page I have Fedco, High Altitude, Johnny’s, and Pinetree. Unfortunately, I don’t think any of them ship to Norway.

Readers, Can You Help?

Do any of you know of other seed merchants that specialize in vegetable seeds for cold climates? If they ship to Norway, that would be a bonus.

Don’t miss our Botanic Interests seed giveaway, going on now through Sunday!

Low of 44F this morning. Yes, this is July. No, not Siberia, or Alaska. Tomatoes prefer 55F-75F at night. Peppers will not set fruit if temperatures drop into the low 40sF. And eggplants? Pollen production is curtailed when temps fall below 55F. But we can eat peas in July!

I hate to admit it to you Southerners, but when the snow melts, what it invariably reveals is…a mess. I’m not just talking about the dead vegetation that needs to be cut back. There’s human-made messes that ought to be dealt with, too. But let’s talk about the plants first.

Cut back and clear out dead plant material

Only March 11th and this catmint is already poised for growth. Most of the crocuses haven't opened yet.

With the exception of the exceptional foliage plants featured in this month’s Bloom Day post, most every plant in the garden is represented by a pile of slimy brown mush when the snow cover finally melts. Some plants get an early start out of the gate in spring, however, and they will look more attractive in their early spring greeness if the brown gook is cleared away.

How do you know which ones are the early ones? Well, that is what your garden notebook is for! Didn’t you make note of which plants put out early growth and write it down so you wouldn’t forget? Let’s pretend you just started your perennial garden last year, so this is your first spring with your new plants. Practice your powers of observation:

Early new spring growth is often a deep redor dusky purple, making it difficult to see. This columbine still needs its dead foliage trimmed back.

I usually wait a little longer before trimming the veronica, because some new growth sprouts from last year's stems. A more ruthless gardener would probably just grab all the stems and make one cut.

Snow removal leaves a mess

I find myself needing to explain things to you Southerners again. When the roads get icy, or only a little bit of snow is anticipated, the highway trucks drive through applying a combination of salt and grit. The salt lowers the freezing point of water and the grit improves traction. When we get significant snow accumulation, the trucks must push (plow) the snow off the road, leaving it piled along the edges of every street. As you might imagine, a lot of that grit mixes with the snow as it is scraped off the road and thrown to the side. When the snow melts, you often find this:

The grit that was used to provide traction last winter shows up on the mud season lawn.

Don’t clean up too much, too soon

It’s tempting to rake away every bit of detritus on the first warm day, but that’s not a good idea. With the loss of snow cover, plants are actually more vulnerable now than when they were buried under the white stuff. We’ve already had a few days in the high 50s and hit 60F once, but this morning at 7am it was 9F. Imagine a plant coaxed out of dormancy being socked with that kind of a temperature drop. I’ve had a lot of plants come through the winter just fine, only to be killed by the vagaries of mud season. Biennials that bring a rosette of leaves through the winter, such as foxgloves, seem to be especially vulnerable. It seems counter-intuitive to cover a plant that made it through the winter just fine, and yet sometimes I wonder if that’s what I should do. Of course, it never occurs to me until after the mercury plummets, and by then it’s too late. And I wonder what kind of material would offer additional protection without trapping too much moisture, encouraging rot. Got any suggestions?

At this time of year, the snow melts more quickly than the ground thaws.

The backstory

As autumn progresses into winter, the temperatures continue to drop. We go from light frost, to hard frost to hard freezes. When the lawn changes from green to a dull tan or gray, we know the soil has frozen because the grass has gone dormant. Some years the snow starts falling before we see this happen. That is a good thing. Snow insulates the soil from the increasingly cold air and gives the woody plants more time to take up water, and the bulbs more time to put out roots. The worst case scenario is when we have an “open” winter, which means no snow. The soil freezes to a much greater depth and plant losses in spring are much greater.

The January thaw

In most years we have a thaw in January where the temperatures reach spring-time mildness and most, if not all, of the snow melts. Ideally this should be a brief reprieve, for if the soil starts to thaw and plants are encouraged to break out of dormancy, they will be killed by the return of winter. After this thaw, we get more snow. Often we get a lot more snow.

Mud season, the real thaw

Sometime in March, the temperatures rise again and the snow starts to melt. This snow melt is often accompanied by rain, as it is this year. Think about the implications. In the winter, as I said, the soil freezes solid. You can not stick a shovel into it, you can not pull a weed out of it. The snow has been insulating the soil, keeping it frozen. When the snow melts, it can not be absorbed by the frozen soil. It runs off our hillside and swells the seasonal brooks.

One of many seasonal brooks that will be dry in summer.

The snow melt can't seep into the frozen soil.

Mud signals the beginning of the end of winter.

A good mud season day from last April. Photo (c) 2008 Cadence Purdy

Plants and people both must persevere through mud season. (March 2008)

Kerry Mendez

It turns out that Kerry was not a born gardener. She took her first nursery job solely as a way to help fatten up the family finances, but quickly found herself hooked, spending her paycheck on plants instead of paying the bills. (I know that is a familiar story to some of you!)

Her interest grew and eventually developed into a garden installation and consulting business, Perennially Yours, that serves gardeners in USDA Hardiness Zones 3-5. Over the past fifteen years, Kerry became increasingly focused on helping gardeners help themselves through her speaking engagements, writing, and garden coaching. Many of her classes are conducted at her home, eventually moving out to her garden to see her lessons working in real life.

I asked Kerry what problem her clients brought to her most frequently. She said they want more color in their gardens. Kerry helps them avoid stocking up on spring impulse purchases and instead choose plants that contribute to the garden design in more than one season. She helps them assess how much time they actually have to spend on garden care and suggests changes to make in design and plantings so that their gardens are not overwhelming to them.

Kerry organized the first Great Gardens and Landscaping Symposium six years ago as a way to broaden the resources she could offer her clients (see separate post below). The symposiums are attended by gardeners from a wider geographical range–visitors come from all over the Northeast–and Kerry says many attendees appreciate the informal sharing of anecdotal stories just as much as the professional presentations.

Kerry and I felt like we had a lot in common and look forward to meeting in person some day. But if you live north of Albany in the neighborhood of Ballston Spa, you might meet her first. If you do, tell her I said hi!

Kerry Mendez (see above) emailed me briefly about the Great Gardens and Landscaping Symposium that she has organized for the sixth year in a row. Since it is focused on gardening with cold hardy plants, I thought it was worth passing on to my readers.

Besides Kerry herself, Paul Tukey, Tara Dillard, and Dr. Mark Starrett will be speaking over the course of two days (which includes the pre-symposium workshop). The workshop and symposium will be held April 24-25, 2009 at the Mirror Lake Inn and Resort at Lake Placid, NY. Topics range from new perennial introductions to organic lawn care and award-winning cold hardy woody plants.

Registrations are still being accepted, but the symposium has sold out the last two years, so don’t wait until the last minute to finalize your plans to attend.

It was a balmy 57F out today, a pleasant change from last week’s snow, so I took a stroll around the garden to see what I could see. I saw the new growth of sedums at soil level, and I saw colchicums emerging from the earth, way too early as usual.

Not all colchicums send up their foliage in early winter, but the kinds that do wind up with browned tips by the time spring actually arrives.

Every year I think I'm going to remember to bring in the rain gauge, and every year I don't. That's why I buy inexpensive rain gauges.

Water expands as it freezes

You were taught this in grade school: water expands as it freezes. You were probably even told that water gets into the cracks of rocks, and actually breaks the rock apart when it freezes. Unless you actually saw this happen, it probably seemed no more than another fairy tale that grownups told, right up there with Santa Claus.

I’m here to tell you: ice happens, and the consequences can be anything from annoying to deadly. It is annoying when the rain gauge you bought at a discount store breaks from the force of the undrained rainwater expanding as it freezes. It happened last year, too. Until I get a fancy self-emptying rain gauge, I will be buying the least expensive rain gauge I can find that measures in tenths of an inch, because I am always thinking I can wait until it gets warmer before emptying the gauge, and then I forget. The force of the expanding ice was enough to break the plastic bracket as well as crack the glass:

Ice happens, and it is a force to be reckoned with. It snapped the plastic bracket as it expanded.

Heaving kills plants

When that same moisture is in the soil and then freezes, the results can be deadly for garden plants, especially newly planted ones. The water in the soil expands and pushes the plant up. When that ice melts, the soil level goes back down, leaving the plant’s roots exposed to the drying air. Cold climate gardeners call this heaving.

Heaving is more common during mud season, that transition time between winter and spring when the soil is subjected to freezing and thawing, but in a weird winter like we’ve been having, it can happen any time snow cover is lost. I was looking for heaved plants as part of my mild weather stroll, but didn’t see any. Any fall-planted perennial, tree, or shrub is at risk (we don’t plant annuals in the fall, silly), but heucheras and primroses seem vulnerable no matter how long they’ve been in the ground. The solution is to discover the plants before the roots have dried, and push them back down into the moist garden soil. Then cross your fingers.

You mild weather gardeners getting a taste of Ol’ Man Winter this year, consider yourself warned. The ice that’s in the ground is just as deadly as the cold air above the ground.

Not too long ago, a reader emailed me and asked,

I bought some hostas and dwarf bleeding hearts to plant. Shortly thereafter I hurt my knee and I can’t go out there and plant them. They are all planted in one gallon plastic pots. How can I safely winter them? If I put them in my garage they will still freeze.

You may have plants in containers that should have been planted, but weren't. How do you winter them over?

It is the roots you are worried about freezing. The rule of thumb is that roots in a pot will effectively be in a situation two zones colder than plants in the ground. So if the plant tag says zone 5 and you are in zone 7 they should be fine.

But I’m guessing you live in a colder place. Definitely keep them outside until the tops die down. You want them to go dormant. After that, you want to put them in a situation where they will stay dormant but not get colder than two zones warmer than the hardiness zone on the tag. That will be different depending on what is available at your place. The garage might be okay, if it gets cold, but not as cold as outside. You could put them up against the house, and surround them with bags of leaves for insulation.

The other thing to consider is the greater the volume of soil in the container, the more insulation the roots will have. A one gallon container is not that big, and won’t have much insulating soil mix for the roots, so you might err on the side of caution and make that three zones warmer than the tag.

I have a drafty, dirt floor cellar that barely stays above freezing. I have put dormant plants in the coldest corner of the cellar and pulled them through the winter. They did start growing sooner than they should have, and made some pale spindly growth, but I very carefully hardened them off and planted them after all danger of frost. It was a pain in the neck but better than losing them.

Recently, Chris of Backyard Gardening Blog published a timeline in pictures, demonstrating the growth of his ‘Endless Summer’ hydrangeas. I found it very interesting to compare his photos with the few I took. You might want to have his post open in a separate tab of your browser so you can quickly flip back and forth to compare shrubs.

May 13, 2007. 'Endless Summer' is just getting started.

June 4, 2007, a bit more than 3 weeks from the previous photo.

June 25, 2008. Click to enlarge photo if necessary.

July 6, 2008

July 16, 2008

July 27, 2008: fully colored up.

September 8, 2008.

Microclimates are important

Chris is in Zone 5. Theoretically I am, too, though not too long ago I would have said I was in Zone 4. I still have a Zone 4 growing season, with later spring frosts and earlier fall frosts. And Chris has one other advantage. Did you notice it? That stone wall behind his hydrangeas is providing a warmer microclimate by storing heat and radiating it back when the temperatures drop.

I have to say I was much happier with my ‘Endless Summer’ hydrangea this year than I was last year. I’m sure it improved its performance that I took care to mulch it with leaves last fall, and I didn’t pull them away from the plant until I was sure all danger of frost had passed. But I can also see that Chris gets more bloom from his ‘Endless Summer’ hydrangeas with the same amount of work.

I hope you found this comparison as informative as I did. A few extra weeks at each end of the growing season and a more favorable microclimate can make a significant difference in the performance of a plant. It’s a good thing to keep in mind when a fellow gardener rants–or raves–about a plant.