Growing Perennials in Cold Climates

A Gardener’s Reading, seventh of 30

By Mike Heger, John Whitman and Debbie Lonnee (University of Minnesota Press, 2011)

For many northern gardeners, the 1998 edition of Growing Perennials in Cold Climates has been the go-to reference for which plants to grow and how to care for them for more than a decade. That edition is still valuable, but for die-hard plant lovers, this revision and update is well worth the nearly $40 it costs.

As I noted in a review of the book in the November/December issue of Northern Gardener, this edition has all the virtues of the original plus expanded plant lists and a rating system that helps gardeners choose among the dozens of plant cultivars that have been introduced in the past 13 years.

Like the previous edition, the revised book includes basic information on how to plant and maintain perennials. The bulk of the book is a perennial-by-perennial assessment of plants that are hardy to the North. What is most valuable are the long lists of cultivars of each variety and the authors’ five-star rating system, which gives gardeners vital information of which among the new plants are keepers and which are just good-lookers in the spring catalogs. For plant types with dozens (daylilies, hostas, coneflowers) of cultivars, the ratings will help home gardeners pick through the hype.

The authors are all respected plant-people with years of experience in northern climates. Heger owns the Ambergate Gardens nursery in Chaska; Whitman is a long-time garden writer and photographer; and Lonnee is a horticulturist who works with plants introduced by Minnesota-based wholesaler Bailey Nurseries Inc. In other words, these guys know their plants.

Growing Perennials in Cold Climates is first and foremost a reference, and it is one you will find yourself reaching for again and again as you plan and care for your perennial gardens.

Best Garden Advice of 2011: Shearing Perennials

Cut back in June, sedum is short, squat and blooming in October.

Back in September 2010, Don Engebretson suggested in Northern Gardener’s perennial column that gardeners shear back some tall, floppy perennials. He wasn’t recommending judicious pinching to encourage bloom and more side growth, but rather grabbing a big ole garden shears and lopping plants off about halfway from the top in late May or June.

His argument was that plants that have a tendency to flop – in my garden that would be Russian sage and tall sedum – will bloom at the time they usually bloom even if they are cut back. Nature programmed them to bloom then, Don said. And, cutting them back results in shorter, stouter stems, and therefore, less flopping. I was wary, but decided to give it a shot.

And, it worked! The Russian sage I cut back in mid-June is still standing tall in October. It bloomed beautifully in late summer and the stems show no signs of flopping over, even as the season winds to a close. The same is true of the sedum, which seemed to struggle after being cut back, but recovered and now are short, squat, and full of bloom.

Thanks for the great advice, Don!

What’s the best garden advice you picked up this year?



Right Plant, Right Place

One of the most repeated mantras in gardening is “right plant, right place.” Like other garden sayings, there is a lot of truth in the advice to choose plants that fit the conditions of a landscape rather than try to adjust the location’s soil, sunlight or micro-climate to fit a desired plant.

Three years ago, I gave up on growing grass in the southeast corner of my lot. We don’t have an irrigation system and don’t want to install one. The corner gets baking sun much of the year. It’s on a slope, so water runs off quickly. Grass likes wet and cool; this spot had hot and dry.

So, out with the grass, and in with a planting bed with prairie plants: grasses, blazing star, Russian sage, perennial salvia, sedum. Now in its third season, I love looking at this colorful bed almost as much as I hated looking at the dry, dead grass that used to be there. And, it’s significantly less work than mowing and watering the area used to be. Each spring, I clean up the area, removing spent plants and stray stems. I usually refresh the mulch and maybe edge it. After that, I just pull weeds, if I see them. In fall, I cut down a few of the perennials and leave the rest for winter interest. That’s the entire maintenance plan.

I’ve only had to replace one plant—a chokeberry bush that didn’t make it through the first winter. Everything else is big, beautiful and soaking up the sun and heat.  Last year, I added these allium because their purple bulbs complement the colors of the ‘Kobold’ blazing star and salvia so nicely.

Right plant, right place. Good advice.

A Well-Behaved Cranesbill

'Tiny Monster' cranesbill

Cranesbills, also called hardy geranium, are noted for their wild look. They can get very scraggly and leggy,  after the first flush of bloom. I usually cut back my ‘Johnson Blue’ cranesbill in early July to keep it contained and encourage more blooms.

But I don’t think I will have to cut back the plant at left, a full, lush, very well-behaved cranesbill called Gernaium ‘Tiny Monster’. A newer cultivar out of Germany, ‘Tiny Monster’ stays about 12 to 18 inches high and spreads only about 24 inches. I love its mounded shape and prolific, deep pink blooms.  In a garden that seems to grow more wild with every rainfall (enough already!), I really appreciate a well-behaved plant.


Do You Say, Pee-O-Nay?

I have always said Pee-a-nee, but I’m surprised how many gardeners I know who say, Pee-O-Nay (accent on the O). And, even though my Iowa husband often accuses me of speaking with what he calls “the Roseville O” (for non-Minnesotans, it’s a long O that you’ve probably heard Garrison Keillor use when he is in full-Lake Wobegon mode), I cannot stretch out the O on peony without feeling odd.

So, do you say pee-O-nay? And, are your whatever-you-call-thems blooming now?

Sedum is an Autumn Joy

'Matrona' in front garden
Sedum 'Hot Stuff'
'Autumn Joy'

The longer I garden in the North, the more I love sedum. It starts out as a dainty little cabbage head each spring, grows into  a perfect green (or purple) background to summer flowers, and then it flowers up in early to mid fall, going from greenish to pink to russet to brown, depending on the variety.

Sedum come in dozens of varieties — tall, short, light green, dark green or purple foliage — and most of them seem to be just as hardy as the rest. The best known sedum is probably ‘Autumn Joy’, a rock-solid plant that I have grown for almost a decade. I divided mine a couple of years ago and now have several nice clumps, which look like they may need dividing again. The popularity of ‘Autumn Joy has led to the marketing of several of its sports, including ‘Autumn Fire’, which is more compact that ‘Autumn Joy’ and has a deeper red bloom, and ‘Autumn Charm’ and ‘Autumn Delight’, two variegated sedum.

Among the more popular sedum now are the purple-leaved ones, such as ‘Black Jack’ and ‘Purple Emperor’. When I created a new front-yard garden a couple of years ago, I debated whether to plant a purple sedum and ended up choosing ‘Matrona’, which has deep purple stems but green leaves. What I really like about this plant is its habit: not too tall, upright, with lots of smallish bloom. Like Autumn Joy, it attracts butterflies and bees galore.  More recently, I planted a small sedum (‘Hot Stuff’ — don’t you love plant names) which has almost lime-green foliage and very dainty blooms. Right now, some Clara Curtis daisies are flopping over it, but that can be fixed with some judicious pruning.

While sedum look good in spring, summer, and fall, what I love most about them is what they add to the winter garden. Leave them standing and soon you will have snow-capped blooms that add an element of shape, texture, and fun to the garden.

What are your favorite sedums?

Volunteers vs. Weeds

When does a plant go from being a welcome  volunteer in the garden to a dreaded weed?

Cosmos and coneflower, a pretty combination, but...

I remember the moment — early in my gardening life — when I discovered that if you left tomato fruits in the garden over winter, they might grow the next year. Amazement! Thrill! Whether the tomato grew to produce the same tomatoes it did the year before, however, depended on the type of tomato (hybrid or heirloom) and its parentage. I still get volunteer tomatoes — tons of them this year because of our near perfect winter in Minnesota. And, occasionally, I let them grow just to see what they produce.

The volunteers that have veered toward weeds tend to be flowers: morning glories (arrghhh!), coneflowers, and this year, a patch of cosmos. I’m letting them go for now, because I like the lacy foliage of cosmos and they provide a colorful edge to my front garden. But will I let them seed? Everyday as I walk through that garden pulling up morning glory seedlings (and maple seedlings from a nearby tree), I think a severe pruning before seed setting might be in order.

What plants do you let go to seed?