conifers: pruning, best cultivars and more, with longwood’s ginny levy
A WHOLE LOT of needled evergreens are getting turned into holiday garland and Christmas trees about now, but those aren’t the conifers I discussed with Ginny Levy, a horticulturist at Longwood Gardens in Kennett Square, Pennsylvania.
With Ginny, who has been at Longwood since 2000 and teaches a popular conifers course in the Continuing Education Division, we compared notes on our top conifers for the landscape, I learned how to prune them, and got a quick review of conifer taxonomy, what “dwarf” really means (hint: not ever-small), and even inspiration on her home-garden collection of conifers in pots.
Listen to the December 7, 2015 show using the player below (or at this link), or read along—or both.
my conifer q&a with ginny levy
Are you allowed to snip anything from the grounds to put in your holiday decorations? [Laughter.] It’s quite a collection there at Longwood.
A. We do; luckily we have such a variety. I don’t do much clipping myself, but we do have our land stewards who go out and do some very judicious pruning, and it does add to our holiday fare.
Q. Dress up those wreaths and garlands!
Let’s start with a brief taxonomic 101, perhaps, just to roughly explain some of the family relationships—especially because with conifers, the common names are incredibly confusing. For instance, I have a big old Eastern red cedar in my front yard, which of course is not a cedar…
A. No, it is not. [Laughter.]
Q. It’s a juniper, and it’s technically in the Cypress family—oh my goodness. Can you take us through some of the biggest family groups and the relationships.
A. You are exactly right, and the red cedars are the biggest group that people get confused with. So many things are called red cedars. One of the interesting things about conifers is they have really large families. The biggest one would be the Pinaceae, the Pine family, and it encompasses a lot of close relatives: the firs, the true cedars, the larches, and of course the true pines themselves, as well as the hemlocks and the golden larches. So it’s a very, very large family.
Some of the other large families are the Cypress family, which is the Cupressaceae family—I love these Latin names [laughter]. That includes your junipers, and some of the Chamaecyparis, Hinoki cypress, that are very popular, and Cryptomeria, which are becoming more and more popular, particularly because the deer do not find them attractive. The dawn redwoods, pond cypress—all of them are in the Cypress family.
There are a lot of similarities within that family, and one of the most striking in my view is the beautiful bark that almost all of them exhibit.
Q. I agree. And then there are the yews—they have a family named for them as well.
A. They do, the Taxaceae, for Taxus. The main two species are the baccata, which are the English yews, and the Taxus cuspidata, which are the Japanese yews. They’re wonderful for their rich green needles, and are the ones that are often used in topiaries. We have a lot of Taxus at Longwood in our beautiful Topiary Garden area.
Then there are the families that are all by themselves. Like the Sciadopitys, or umbrella pine—which is not a true pine—with its rubbery foliage [detail above; pyramidal plant below] that’s wonderful for Christmas greens.
Q. I have a big Sciadopitys that as a beginning gardener I moved from my first garden in Long Island to upstate New York. I brought the umbrella pine with me in a bushel basket, and I planted it in what I didn’t even understand was two zones colder, and plopped it down in a spot and didn’t know what would happen—it was kind of a rare plant then, 30 years ago.
And now it’s taller than my house [laughter] and very happy—so I got very lucky with that rarity.
A. You bring up a good point: We tend to look at these zone requirements, and sometimes we’re not adventuresome enough. The trees do not read the books—we know that. [Laughter.] But either you have a great microclimate, or just the tree is a nice, healthy tree and is happy in its space.
I know I kind of push the borders in my property, which is very open and windy. But I love the deodara cedars (Cedrus deodara). They’re supposed to be marginally hardy here, but I am knocking on wood; I have had wonderful luck with them. I just love their gracefulness, so I try anyway.
Q. We’ve talked about who’s related to who. Within these families are there common physical attributes that give us clues about them?
A. There are some overarching characteristics—say, for instance, in the Pine family and pines in general. They tend to be a much straighter, singular trunk. Oftentimes they will open up more with age. They tend to grow with whorls of branches—the branching habit is like a wagon wheel.
The pines are distinguished by having needles in bundles, or fascicles. One of the first things you would do if you were trying to tell one pine from another—one of your starting points would be to count the number of needles in the bundles. Our Eastern white pine (Pinus strobus) has five needles. Five needles are the most common, but there are also three-needle pines and two-needle. That’s going to give you your best starting place.
Q. Some clues to ID.
A. Yes. Within the larger Pine family, you have the other genus of spruces, or Picea. They tend to be a looser habit. Their needles are singly held, and when you pull a needle off a spruce and rub it between your fingers it will roll. It’s actually square in cross-section.
A. That’s a good way to tell it apart from a fir. When you pull a needle off a fir, it’s flat, so you can’t roll it at all. We just have a little saying that, “firs are friendly and spruces are sharp.” When you put your hand up against a spruce, oftentimes it will give you a little jab, where the fir has a nice, soft touch to it.
Q. Two of my other favorite conifers in the garden are the concolor fir (Abies concolor) and some of the nicest ones have almost a turquoise-gray-blue to them. And then the Korean fir (Abies koreana) I love also. [Above, the concolor fir.]
A. Well, you’re definitely speaking my language. I would say those are two of my favorites. I love the Korean firs.
I have a lot of my conifers in containers. About three years ago we bought a property next to us, and that really allowed me to expand the palette of larger trees. But before that where I had kind of constricted space, I grew them all in containers.
I’ve had wonderful success with them. We’ve had really cold winters these last few years, but they really hold up well.
I’ve actually done the evolution from the fancy containers with all the different flowers, and then I went to shrubs, and then I actually went to some other types of trees—and now I am really hooked on the conifers because they’re so easy and undemanding.
Q. Are these very large weatherproof pots, or do they get stored somewhere in winter?
A. No, I actually keep them out. They are ceramic, but quite heavy. Some of the worst days I have pulled them up closer to the house. But one of the things I do: I line my containers with bubblewrap, and then put the soil in. What that does, it just gives that cushion, because the main problem with having container outside in winter is when they expand…
Q. …freeze and thaw; right—and it breaks them.
A. Right. The bubblewrap gives you enough cushion to give you the extra play. I have one or two pots that over the years have cracked a little bit, but I must have 10 or 15 conifers in containers.
Q. It’s a great idea.
One of the most common questions I get—and I bet you do, too—is about pruning of some conifer or another. It can be truly mystifying to grasp which ones respond well and how far back you can trim or not. Is it memorization that I need to do, or are there clues about pruning, things I can observe?
A. I think the best thing to do is really look at the leaf structure. When you look at things like Thuja or arborvitae, Chamaecyparis or Hinoki cypress [above], they are going to have fan-like leaf structures. They are actually easier to prune because you can go back to a bud and prune in the direction that you want it to grow.
Generally with conifers, you don’t want to prune them unless you really have to. Oftentimes people find that they place them too close to their house.
Q. [Laughter.] Yes!
A. They start small, and some of the descriptions can be a little bit misleading. Basically the ones with the fan kind of foliage: You can prune those pretty easily by going back to where another branchlet is coming off.
The other ones are a little bit different in the fact that they are going to put out one big growth spurt a year, most of the time in the early spring, and you’ll see that protrusion of the new foliage, which is actually encapsulated. We call it a “candle,” and it can look quite lovely. Especially on the black pines, it can be white and really a very attractive feature.
When that expands, at a certain point you want to kind of tug on it with your hand. You want to get to the point where you can snap that candle off. It’s better to do it with your hand, and I would advise wearing gloves because the resin can get quite sticky. But if you use clippers it can sometimes make brown tipping at the ends of the foliage, where it doesn’t do that with your hand. People do that a lot with the really miniature or dwarf conifers, when they want to keep them quite small.
Q. It’s like we are pinching them, as you might pinch a perennial when it’s coming out of the ground to keep it more compact. We’re pinching the fresh growth?
A. That’s exactly right. You’re just going to break that little tip right off. It will feel like when you break asparagus—it lets you know exactly where it wants to be.
Q. I have to confess with the umbrella pine, or Sciadopitys, years ago I did do that once. It kind of made it fuller. It was feeling a little loose, and it kind of thickened it up, and made it look better. It was quite a job.
A. You’re right, because they still have those dormant nodes that are back further in the branching. A lot of times people will do that to fill it out just a little bit, especially if it’s been grown in an area where it’s not quite getting enough sun, or hasn’t been quite happy enough. Maybe a little bit of a drought situation and it gets a little thin—you can thicken it up quite nicely. But it can be laborious.
Q. Especially on a bigger plant.
So with the conifers that have these flattened leaf structures like the Thuja or arborvitaes, are better inclined to a little pruning if need be.
A. You really need to look at it for a bit and think about what you want to do. Other than like the Taxus, or yews…
A. They really can be rejuvenated. There are certain things like the beautiful Cunninghamia or China firs [detail above], which is not a true fir—but that one can actually be cut back to the ground. If you don’t have the space to have the lovely large China fir, you can use that as a cutback shrub, and have that wonderful new flush. There is a cultivar named ‘Glauca’ that is kind of the same of the concolor fir, as you were saying—it’s giving you that wonderful blue soft color in the landscape.
Q. That’s a favorite. I don’t think I can grow it where I am, but in my earliest garden I had a Cunninghamia, and I still miss it.
Let’s talk about dwarf conifers for a minute. What does “dwarf” mean—and I say that having two dwarf white pines (Pinus strobus ‘Nana’) that after 30 years aren’t very small, Ginny. [Laughter.] Dwarf doesn’t mean stays small forever, or permanently miniature. [Photo above.]
A. What the classifications really mean is the speed of the growth. A dwarf is considered a tree that is going to grow between 1 and 6 inches a year. So over time, a dwarf is going to get quite large, but it won’t happen quickly.
If you want a true tree that is going to stay small, you need a miniature. These are classifications that are given by the American Conifer Society. A true miniature is going to grow less than 1 inch a year, so in 10 years, you’re going to have a foot-tall tree. At some point in 1,000 years that tree will be too tall for your house—but it’s not going to happen quickly.
Q. We both agreed we love some of the firs, such as Korean and concolor firs. If you’re telling us what to catalog-shop for this winter or look for in the nurseries next spring, what are some conifers that are your favorites?
A. I love the Oriental spruces, Picea orientalis. They’re kind of a more refined Norway spruce, with the smallest needles of the spruces. Oftentimes they’re dark green—a really lustrous green—but there are cultivars that go to a darker green. And there’s a gold Picea orientalis ‘Skylands.’
A. Another that I really like is one from our Eastern white pine, Pinus strobus ’Louie.’ It is a golden conifer that really glistens in the sunlight, and catches your eye.
There are so many cultivars of Hinoki cypress; there is one for everybody. But one I particularly love is ‘Crippsii.’ Do you know that one?
Q. Oh, I think our gardens are separated at birth, Ginny. [Laughter.] I have three of them, one that’s one of my oldest plants here [on right in photo below], and I can’t imagine gardening without them. It’s a treasure every day of the year.
A. This is so wonderful. We are kindred spirits for sure.
A. That is—that is one that hasn’t changed names, so we’re very happy about that.
I would be remiss if I didn’t say the Abies koreana—there is ‘Aurea’ that I love, and ‘Silberlocke,’ where the needles are so upturned that you’re seeing the white lines underneath, so it give you a bluish-glaucous look that’s really lovely.
Q. So again, that’s a little something extra when you see that flash of the light color underneath.
A. With the Abies concolor ‘Blue Cloak’ or ‘Candicans,’ you just can’t beat them.
Q. Favorite ones for cones? I love Abies koreana cones because they’re sort of purple [top of page photo].
A. I always say the firs are the cone queens of conifer world. Unfortunately they don’t last—a lot of the pines are woody, and last.
I tend to love the Metasequoia glyptostryboides, the dawn redwood cones. It’s a massive tree, and the cones look like little baby honey stirrers.
Q. That’s a great description—baby honey stirrers [photo below].
A. As a matter of fact, in my last class, two people made me earrings from Metasequoia cones, and one made me a little crown.
Q. That is so sweet—and a perfect ending thought with the holidays coming. What a great gift: Metasequoia earrings. Thank you so much, Ginny.
- The Longwood conifer class (in Kennett Square, PA), with Ginny Levy
- The Longwood Plant Explorer database, including conifers in the collection
- Visiting Longwood Gardens
- The American Conifer Society plant database
- All my conifer stories on A Way to Garden
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(Photo of Ginny Levy and of Cunninghamia from Longwood Gardens; rest in Margaret’s garden.)