Sciency Answers: Pruning dormant roses

Esther over at Gaias-Gift has a question:

A number of us are discussing a common wisdom thing about not pruning your roses before the forsythia bloom or only when the buds start swelling. The implication that I will harm my roses by pruning before they start to come out of dormancy doesn't exactly make sense to me. ...the implication of what people say is that pruning in late winter, before they come out of dormancy on their own, brings them out of dormancy too early, making them more vulnerable to freezes than they would otherwise be. Is there any science to support that?

I love getting questions like this! I've heard this since I began gardening, and never stopped to wonder if it is true, and if so, WHY?

Pruning can break dormancy

So I've been poking around, and it turns out that yes, pruning woody plants can cause them to break dormancy earlier. Most of the research on the topic is in grapes, but from a very different perspective than those of us in cold climates worried about late freezes. Rather, I found a lot of research on growing grapes in warm, semi-tropical climates where there isn't enough cold to break dormancy naturally. In Taiwan, is appears, grape growers can keep their vines growing without a winter by using a combination of severe pruning and plant hormone treatments. But it isn't just in grapes. I found studies of cherries, peaches, and apples with similar findings. So many woody plants are stimulated by pruning, even when they are dormant.

More susceptible to freezing?

Interestingly, though, the one paper I could find that actually measured the winter hardiness of developing buds at several time points after pruning didn't find any change, so there isn't direct evidence that early pruning will lead to more damage from late freezes. That isn't to say it doesn't happen, however. Cold hardiness is notoriously hard to study because there are so many factors from moisture to time to temperature that make it very hard to recreate the real world effects of cold in the lab, so just because one group of researchers weren't able to find a difference doesn't mean there isn't one.

Why?

But what gives? I mean a dormant rose bush is just sitting there. How and why does it respond to someone cutting bits of it off? Well, I found some papers looking at dormancy in grapes, and they found that dormant buds are really quite busy, with many genes still being actively expressed. The also found that during natural dormancy breaking, the hormone auxin peaks in the buds a full two weeks before any visible bud swell. So, in late winter, when your plants look like they are just sitting there, they aren't. Genes are doing there thing, and hormones are churning, and when you take your pruners and lop something off, you change the patterns of gene expression, the flow of hormones, and can stimulate buds to break dormancy and start growing.

The bottom line: wait to prune

It looks like the advice to avoid pruning too early in the season is good. By pruning too early you can cause them to begin growing to early, and result in more damage from late spring freezes.

Another hardy succulent to love

I love succulents, and spend inordinate amounts of time pining after agave, aeonium, and aloe that I can't really grow here. But I've been finding more and more hardy succulents that perform beautifully in my climate. Here's one of my latest loves, Orostachys spinosa

I love how the rosettes of succulents often look like flowers. This one reminds me of a gerbera daisy! And fully hardy with reasonable drainage. Mine is in a fairly well drained spot in the open garden (ie, not a rock garden) and has been fine, even this year of the never ending rain. I got mine, of course, from the amazing folks at Arrowhead Alpines, though other people carry it as well.

The Survivors

The snow has melted, crocuses are blooming, and it is time for my annual "I wonder what survived" tour of the garden.

We had what I thought was a pretty average winter -- some serious cold, but nothing too intense. I was worried because we didn't have very good snow cover (snow = nature's blanket) but so far things look great!

After having it 4 years, you'd think I'd have gotten used to this Agave parryi actually being hardy, but every winter I'm happily surprised to see it come through unfazed. Some years the tips of the leaves get damaged it they weren't covered with snow in the very coldest weather, but this year it didn't even get that. It has decent drainage in this spot, which I think is a big part of my success.

This is one of my snapdragons... Pretending to be alive, though I'm pretty sure it isn't. I don't know why snaps do this for me -- it seems they always come out of winter looking fine, and then collapse once actual spring arrives. Little teases...

When I saw the slimy wet mass at the heart of this cardoon, I thought it was a gonner, but looking closer I see a tiny fat white shoot coming up to one side. We'll see if it actually pulls through.

I was VERY surprised to see this bud pushing up through the mulch. It is an Anemone coronaria, which I've always seen listed as zone 7 or even 8! I grew them as an annual last year, and figured that was that. But apparently not! And I'm not the only one. Kylee over at Our Little Acre (also zone 5 -- just a little south of me) said she's had them come back for the past three years!

So, very good news on the winter survival front here! I am SOOOOOOO excited about the gardening year starting up! Let me leave you with some totally gratuitous crocus shots:

Agapanthus

 What is that white flower, looking stunning (ever slightly floppy) behind my 'Matrona' sedum? Oh, just some agapanthus. Why yes, I DO live in zone 5. Hmm? Oh, yes, agapanthus are generally only hardy to zone 7, at best. Do I bring it inside for the winter? No, this is a hardy version! You didn't know zone 5 hardy agapanthus existed? Well, neither did I until I saw it in the Arrowhead alpines catalog.

Echium enthusiasm

It started, as these things so often do, with the Chiltern Seeds catalog. Their thick catalog of lust-inducing descriptions (and no pictures) arrives every winter, and I discover some new group of plants I just HAVE to try.

How could I pass up this description of Echium lusitanicum ssp. polycaulon?
"From Portugal comes this delightful and little known plant for the border. Forming three foot rosettes of large, bristly leaves, it produces over a long period in late spring and early summer many softly hairy stems bearing 18 inch spikes of lovely, vibrant pale blue flowers with violet veins and gracefully protruding stamens. Recommended as a quality cut flower. 3 ft"

Or this, of Echium russicum?
"From Eastern Europe comes this superb species producing bushy specimens with attractive, slender, pointed, white-hairy leaves, and bearing rather splendid, twelve inch spikes of bright dark red or crimson flowers charmingly garnished with long-protruding red filaments. Definitely something different for the front of your borders and, although often thought of as a biennial, it will often become a short-lived perennial if it gets to like you. 2-3 ft."

So last year, I ordered the seeds (along with some E. vulgare 'Blue Bedder' and E. fastuosum). Last summer they just made little rosettes, but they over wintered, and now are showing their stuff.

E. russicum is in full bloom right now, and I'm in love with the delicious raspberry crush color:

The plant as a whole is a little loose, but would look great in a densely planted boarder, and I'm excited to try them as cut flowers.

According to what I could find on-line, E. lusitanicum is only hardy to zone 7 -- but they overwintered just fine for me (though last winter was a mild one) and are just starting to send up their flower spikes. I can't wait to see them in bloom.

 

E. fastuosum isn't hardy, the ones I left outside died, but I overwintered one in a big pot inside. It is looking pretty lopsided from the long, dark, Michigan winter

But the foliage is still amazing, and I'm hoping for flowers this year.

Anyone else growing Echium? I think this is an obsession that is just beginning... Chiltern offers another variety, a hybrid called 'Snow Tower' which they describe as being "almost unbelievable – an enormous plant producing an enormous avalanche of snow-white flowers. Up to 15 ft" Can you imagine? 15 FEET of echium goodness! I'm sure it will be next to impossible to over winter... I'm also sure that won't stop me from trying!

Annual Arrowhead Alpines Assignation

I took what I try very hard to make my annual trip to Arrowhead Alpines recently. By which I mean that I try very hard to go ONLY once a year, because I have yet to go without my bill somehow mounting into three figures. And that isn't because they are expensive -- prices are quite reasonable, they just have SUCH amazing stuff I can't resist.

If you don't know Arrowhead, you should. They are one of the great specialty rare plants nurseries in the US. They do mail order, so no matter where you live, you've no excuse not to browse their wonderful catalog, especially if you live in a cold climate. Unlike the tempting (but rarely hardy in Michigan) Plant Delights Nursery, Arrowhead is smack in the middle of zone 5, and their selection of plants for this climate is amazing. They have hardy versions of typically tender plants like agave, agapanthus, and gazania, and all kinds of other cool stuff.

This year I sampled some of their amazing primrose selection. Below are two of the Primula xpubescens 'Gigantea Select' I picked out. Their catalog says "Perhaps the best primula for Midwestern gardens, they laugh at summer heat, flowers are huge in a wide range of colors." With that recommendation, and these colors, how could I pass them up? If these perform as hoped, I'll be getting many more.

 

I also discovered a hosta I actually like! Like so much I couldn't pass it up. This little charmer is 'Pandora's Box' I bought a little pot, and easily pulled it apart into 20 (yes 20!) little divisions, which I spaced out to form a low mass in the front of the shade garden. They look a little sparse this year, but they should fill in next year.

On the subject of foliage for shade, I also couldn't resist getting another couple of their gorgeous Cyclamen hederifolium. They have a wide range of leaf types -- from mostly green to almost pure silver, but I like these intricately patterned ones best:

The plants I got are small, but the one I got from them last year has already grown into this spectacular clump. I'd grow it for the leaves alone, but they also are topped with a mass of fragrant pink or white flowers in the fall. Sure beats hostas!

They have a mind-boggling array of Sempervivum (I've never counted, but I think there must be over a hundred varieties listed in their catalog, and more at the nursery itself) which are so charming and so easy I never leave without picking up a new one. This time it was this bright red variety called 'Mona Lisa.' I can't quite believe the color! I wonder if it will hold all summer?

I got oodles of other things... a hardy cymbidium (yes! I'm not kidding!), lots of campanula (I've finally promised myself I will stop ignoring that genus) and so much else -- but none of them are flowering or looking pretty at the moment, so I'll save them for another day. I'm also trying to talk myself into going back... there are geraniums I wanted, and... well, we'll see.

I really think they are alive!

I think my Agave perryi 'Super Hardy' have lived up to their name!
The big one looks absolutely undamaged -- no mushyness or anything:

The small one (a pup from the big one) isn't quite as happy, with a few mushy leaves, but the damage seems to be just on the outer portions of a couple leaves -- no signs that the center of the plant is rotting out.

I'm so thrilled! I didn't even give a special spot -- I put them in a relatively well-drained part of the garden, but no special rock garden treatment or anything. Who knows it they will prove to be reliably hardy over the long run here in zone 5 (unlike the rest of the country, we had a slightly milder than usual winter) but I think I could recommend them with confidence in zone 6. The sad news is that I no longer know of a source for it. I got mine from the always amazing Arrowhead Alpines but they don't list it in their catalog for this year. Luckily it seems to make pups pretty freely, so hopefully I'll be able to have lots of them soon. And you never know -- we you visit Arrowhead in person, they often have plants that didn't make it to the main catalog. If I can, I'm getting more.

The agave lives (for now...)

I thought for a moment we were going to see the ground -- we had a string of warm (highs in the mid 30s!) temperatures, and snow was melting. Of course, we got about 4 inches last night, and are supposed to get 4 MORE today, so I guess seeing the ground will have to wait a while.

However: while poking about outside in the heat wave, I did see this poking up out of the snow:

My Agave Parryi 'Super Hardy'! It lives! At least for now... It has made it through the real cold of winter, but still to come is the perpetual wet of early spring. But it is alive! I hope everything else I'm worried about makes it too.

Goodbye and good luck!

The national weather service says: "Snow showers likely, mainly after 7pm. New snow accumulation of around 1 inch."

So, winter is here, and soon my plants will just be lumps and bumps under the snow. Most of my plants, of course, are old hands at this winter thing, and shall breeze through it just fine. But every year I try at least a few things that aren't SUPPOSED to be hardy, just to see. So today, before the snow starts flying, I went and said goodbye and wished them luck... Here are a few of the things I'm HOPING to see again in the spring:

 This is Agave parryi 'Super Hardy'.  The Arrowhead Alpines catalog says "from the most cold hardy population we know." I've put it in the best drained spot in my garden, and where it will be piled deep under insulating snow when I shovel my walk, so let's hope it lives up to its name!

Ophiopogon plansicapus 'Nigrescens', black mondo grass is such a cool plant, but all the references seem to say it is only hardy to zone 6. But that is just one little zone colder than here... I just have one test plant this year -- if it makes it through the winter unscathed, I'm going to get a bunch more and mass them in the shade garden.

This is a very, very bedraggled looking Echium fastuosum I grew from seed this year. Yes it looks bedraggled, but it is supposed to be only hardy to zone 8 and we've had already had temperatures dip into the 20s, so what do you expect. Actually, I had fully expected it to be dead by now, and I dug up one to bring inside before our first frost. But since it is still hanging in there -- still has green leaves even -- I've decided to hope against hope, mound up a protective layer of mulch thick over its lower branches and see what happens.

I've got other things I'm hoping against hope survive: Verbena peruviana, Leptinalla squalida 'Patt's Black' (Arrowhead says it 'needs some protection here' so we'll see), some roses in the cutting garden, and a few other oddaments.

What are you gambling on this winter?