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The crew from Gardens and Grounds here discusses Monticello's modern, historic, and unrealized greenhouses, and share tips and techniques for caring for your plants during the winter.

Featuring Michael Tricomi, Manager and Curator of Historic Gardens; Peggy Cornett, Curator of Plants; Debbie Donley, Flower Gardener; and Robert Dowell, Senior Nursery Associate at the Thomas Jefferson Center Historic Plants

 

Michael Tricomi: It's January at Monticello, typically our coldest month of the year. But the mountaintop has a stark beauty. When you stroll around the gardens and grounds, it feels quiet and contemplative.

But we’re actually doing a lot of work inside right now in our greehouses and that's what we're going to talk about today.

This is “A Rich Spot of Earth,” a podcast about gardening and the natural world. I’m Michael Tricomi, Manager and Curator of Historic Gardens at Monticello, Thomas Jefferson’s home in Albemarle County, Virginia.

Historic Greenhouse

Michael Tricomi:

In the 18th century, freestanding greenhouses, also called orangeries, became fashionable in Europe and Jefferson saw quite a few while traveling in Britain and France. In America, they were less common, but Jefferson's friend, William Hamilton, had an enormous greenhouse at his home near Philadelphia. He also had several hot houses, or heated greenhouses, filled with unusual plants he collected from around the world.

Here's Curator of Plants, Peggy Cornett, and Flower Gardener, Debbie Donley, discussing Jefferson’s greenhouse.

 

Peggy Cornett:

Jefferson had an interest in growing plants that needed protection or a greenhouse of sorts as early as 1778, when he got an acacia plant. He was very interested in plants that would be grown in Orangeries, such as what George Washington had at Mount Vernon. That one had an area behind the main back wall where you could have fires. It's a couple stories high and it's quite sunny and the back wall is whitewashed to reflect. And, of course, people were forcing citrus trees to produce fruit, to ripen fruit, and also to grow fragrant plants. The acacia and the citrus have very fragrant flowers. It was a real luxury, like, you know, a gentleman farmer, would be able to do that.

 

Michael Tricomi:

Jefferson sketched ideas for two different freestanding greenhouses, but neither one was ever built. Ultimately, he settled on something more modest, designing a small, glass-enclosed space attached to the main house. He called it the South Piazza.

 

Peggy Cornett:

The greenhouse that was built at Monticello was completed when Jefferson was retiring from the second term as president in 1809. The South Piazza is right next to Jefferson's, sanctum sanctorum, next to his library, his study, and his bedchamber. So it was on the side of the house, where Jefferson spent a lot of his time. And it connects to the South wing or the terrace.

 

Debbie Donley:

And it's amazing, it's unheated, but we keep citrus and acacia out there year-round. There is a lemon and an acacia and a geranium. At one point we were monitoring the temperature and it would get below freezing in there, but they did okay.

 

Peggy Cornett:

Yeah, I think it might've been fine for Jefferson, but there were a few years where it was so cold that I think everything froze in the greenhouse. It was down below zero.

 

Debbie Donley:

Yeah, that'll do it.

 

Peggy Cornett:

It was so cold that when he was trying to write with his quill pen, the ink would freeze in the well.

 

But in the later years probably after 1816, the greenhouse appeared to be a storage space where Jefferson kept seeds a seed cabinet and seed vials. And and there was also a work bench that was used and some of the last references to the greenhouse let us know that it was a place where Jefferson's many grandchildren played and it was a place to sit and enjoy reading, on a patio more or less.

 

Debbie Donley:

All the windows are triple sash windows, so they can raise up. So in the summer, it's just a beautiful place to sit with the cross ventilation and it's just really nice.

 

Peggy Cornett:

Yeah, you have to lift them up and prop them up with some bracing.

 

Debbie Donley:

Right. There's sticks that hold them up. But also in the winter, the sunrise out there is beautiful. The glass will have ice frozen on it and yet the sunrise will come through the windows and melt the ice. It gives you this nice pink tinge.

 

Chasmanthe and Geranium

Michael Tricomi:

In 1812, Jefferson received several shipments of South African bulbs that he may have planted in pots in the greenhouse.

 

Peggy Cornett:

His friendship with Bernard McMahon, a nurseryman and seedman in Philadelphia, also gives us clues into plants that he was receiving that could have been grown in a greenhouse, such as cape bulbs, which were plants that were just being introduced from South Africa. They're tender bulbs.

 

Debbie Donley:

And, actually, we just put a Chasmanthe in because it's getting ready to bloom.

 

Peggy Cornett:

That was one of the South African plants. The foliage is sword shaped. It's tall, actually. And the flowers are orange and they're quite pretty.

 

Debbie Donley:

They're reddish orange. But they are on long spikes and there'll be several flowers per spike and just nice bright green foliage. It gets about four feet tall. So I do put some bamboo or stakes just to support them because once they start really blooming, they tend to flop a bit, but they're just beautiful. It's quite impressive.

 

Peggy Cornett:

The name Chasmanthe, I think it's from the Greek word for chasm because the flower is supposed to look like a gaping mouth.

 

Debbie Donley:

It looks like a flower a hummingbird would love. Yeah.

 

Michael Tricomi:

The Latin name for that plant is Chasmanthe aethiopica. Jefferson didn't always record which plants survived. But if he had any success with his South African bulbs, it would have been with this species. It grows so abundantly it's considered a weed in southern California.

 

Another South African plant that became popular in America in the early 1800s was the species geranium -- meaning a geranium you'd find in the wild. The Latin name is Pelargonium inquinans and it's a parent of our modern geraniums that are popular today.

 

Peggy Cornett:

Jefferson did, possibly, grow the geranium in the greenhouse. Jefferson kept a plant when he was president in his cabinet in the President's house. And when he was returning to Monticello his friend, Margaret Bayard Smith requested that he leave her his plant. She was very lovingly wanting to have this plant as a remembrance of Jefferson. And he was embarrassed about it because it wasn't looking very good at the time. He said, "I'm sure your fostering attentions will revive this plant." And he did take cuttings of that geranium back with him to Monticello.

 

The geraniums we grow today, usually they're a big double round-headed flower and these species geraniums are just much simpler. It's quite a nice orange red color.

 

Debbie Donley:

And they also are quite a bit taller, like five feet tall, looks like a tree with a geranium on top.

 

Peggy Cornett:

But to keep it as a house plant, you can just cut it back regularly.

 

Debbie Donley:

We've cut a lot of them back just recently and now they'll put out new growth and be nice and bushy again.

 

Debbie Donley:

A lot of people think they need full sun, but, actually, when they're out in the garden in the summer or in pots in the summer, they do appreciate a little shade in the afternoon.

 

Peggy Cornett: And you grow them in the garden as well?

 

Debbie Donley:

I do. I move them into the garden, after danger of frost, and then we dig them up before the frost hits and put them in pots and they overwinter in the greenhouse. And then we put them back out there in the spring.

 

Peggy Cornett:

They're tough. You can let them get quite dry. And some people just practically let them go semi dormant over the winter.

 

Debbie Donley:

I've heard of putting them in a brown paper bag in a basement or a root cellar and just let them sit there all winter. And then pot them up in the spring. I haven't tried it.

 

Peggy Cornett:

I haven't tried that either, but I've heard that it does work. And the other thing I know when I used to take cuttings from them that I would take the cutting and let it sit on the bench for a bit to callous off a bit before I stuck it into the rooting media. That seems to keep the root cutting itself from rotting at the base. That was my technique.

 

Michael Tricomi:

It can be hard to find Species Geranium today, but our Center for Historic Plants propagates and sells it.

 

Visitor Spotlight

Michael Tricomi: Now let’s hear from some recent Monticello visitors.

"I'm Chris and I'm from Washington state, and it's been lovely walking around the grounds impressed by the depth of knowledge of everybody involved and a lot of thoughtfulness about the challenges different generations face and the difficulties sometimes to face up to those challenges."

 

Modern Greenhouses

Michael Tricomi:

We have two greenhouses at our Center for Historic Plants, where we propagate plants for sale. And we also have two greenhouses on the mountaintop, where we grow plants for the historic flower and vegetable gardens.

Horticulturist Robert Dowell joined Peggy and Debbie to talk about greenhouse propagation.

Robert Dowell:

Our primary greenhouse, the ambient temperature in there is between 70 and 80 degrees, and the main goal is to propagate cuttings and to give a good germination environment for seeds. And so there's about 16 movable benches in the greenhouse that we can get between and water and tend the plants as we need to.

And six of those benches have bottom heat coils because a lot of species that germinate from seed need a specific temperature to germinate at usually somewhere between 70 and 80 degrees. And they're just rubber coils fed with a hot water heater to keep that temperature up.

Debbie Donley:

If you're going to try and propagate your own seeds at home, I highly recommend purchasing a heat mat. They're not that expensive and it just that's what some seeds want and need. And the germination percentage is just huge.

Peggy Cornett:

And the nice thing too is you don't have to keep the ambient temperature so high. Mm-Hmm. Which is better because the higher you put the temperature, the more chances you have for insects develop and that sort of thing.

Debbie Donley:

We also put plastic covers over our flats. When we first sow the seeds, it gives them more moisture, more of a little mini greenhouse effect, so that helps a lot. And you have to be careful because they can get too wet and start molding and rotting but there's a lot of little tricks to growing seeds to be successful with it. But it's not hard. You just have to read up a little bit about it before you do it because it's fun.

Robert Dowell:

Yeah. And each species has a different personality to tap into to find out how to propagate it. Like Debbie was saying some don't need that cold period and they can just go right on the heat, whereas a lot of seeds need three months of a stratification period, where it's basically your simulating winter. So at CHP we'll have flats sewn that go in our walk-in cooler. Where it's kept at 34 degrees or so, and they might sit there for two or three months and then we'll pull them out and put them in the greenhouse and give them bottom heat.

 

Debbie Donley:

and some seeds even, the outside coating is so hard that it needs to be nicked a little bit.

Peggy Cornett: Or file or nick it.

Debbie Donley: Sanded or whatever.

Robert Dowell: Soak sometimes too.

Peggy Cornett: An overnight soak is good.

Robert Dowell: And exposure to light, I think the general rule is the smaller the seed, the closer to the surface of the media it needs to be. So if the seed looks like dust, it basically needs to sit on the top of the soil. Whereas if it's an acorn, it can go probably four inches down.

 

Debbie Donley:

So it does pay to look up and understand what the seed wants before you try and propagate it.

 

Water / Soil

Michael Tricomi:

You need to think about watering and soil or media as well.

 

Robert Dowell:

At CHP they have an overhead mist system. The minute you take a leafy cutting of a plant and you wanna propagate it, it's a race against the clock before that cutting dries out. And so the intermittent mist system, we can dial whatever frequency we want, and that'll give it that steady stream of mist to help it stay alive until it can root out.

 

Debbie Donley:

And another thing we do we have big trays of water so they absorb the water from the bottom up. If you're overhead watering, even if it's a fine mist, you can displace the seed in some seeds like to sit right on top of the soil. Some like to go down a quarter of an inch, some like to go an eighth. It just, depends. And so a seed that is sewn right on the top, if you're overhead watering it, it's gonna move it around.

 

Peggy Cornett:

And it also compresses it sometimes too. And so it's better to soak it up from underneath.

 

Debbie Donley:

And then you get into your potting soils. Some are better than others as far as absorbing water. Whereas other types readily absorb the water, leave it in there an hour, it's ready to go out and get on the mat.

 

Peggy Cornett:

At CHP you're switching some of your media, which is interesting.

 

Robert Dowell:

We we've had problems in the past where our media just wasn't coarse enough, and so, like you were saying, Peggy, over time, overhead watering compresses the media and that can become a problem. So anytime you can increase the amount of coarse material in your media, like perlite is the standard used in the industry. But we're trying to move away from perlite if we can. We've used rice hulls in the past and that's been a good substitute for filling that porosity need.

 

Robert Dowell:

And some seeds are more tolerant of yuckier soils than others. some species are very tolerant to soil type and some are very specific. So it's just knowing what species you're growing is the best thing you can do.

 

Debbie Donley:

And that's also another point to make is when you're doing these seeds, keep up your journal so that for next year that this didn't work too well or this worked great. I'll do it again. It's just so easy to forget what worked and what didn't.  

Cooler Greenhouse

Michael Tricomi:

We have a cooler greenhouse as well.

Robert Dowell: And then our second greenhouse, that's gonna be between 30 and 40 degrees. And the goal with that greenhouse is to allow us to overwinter more tender woody stock. So things like figs, we're gonna start growing pomegranates too. We also have rose cuttings. Roses are fully hardy, but when you have recently rooted cuttings that are very small in small pots, they're not suited to overwinter outside. So it's best to have them in a protected environment that's cold enough to stimulate winter but not so cold that they get freezing and not so warm that they try and actively grow. And as we move towards spring and the days get longer and warmer, we'll let that house gradually warm up on its own and then things can break bud and be a little bit ahead of the season.

 

Fig Cuttings

Peggy Cornett:

You mentioned you were taking fig cuttings and that's a fun topic.

 

Robert Dowell:

At CHP, usually between Thanksgiving and New Year's is fig cutting season. They're hardwood cuttings. So they'll be leafless. We'll propagate three varieties of figs: the Green Ischia, the Marseille, and the Brown Turkey.

 

Robert Dowell:

We'll harvest branches that are about, I wanna say, like a Sharpie permanent marker, like about that diameter, and we'll take branches that are three, four feet long, and we'll cut those into sections, about six or eight inches long. And it will have several nodes. And those nodes are the old growing points where there were leaves. And from each of those nodes is the potential for a new branch to form.

 

So you just, have a bare stick, no roots on it. And we'll put those into a potting media, which is usually very much on the coarse side. So we like to use a perlite-vermiculite mix. Figs are pretty adaptable, but I try to avoid using too much peat, because peat tends to hold a lot of moisture. And so we'll put these sticks basically in this media and put those on bottom heat and then they will root just like that.

 

Robert Dowell:

Some cuttings are very finicky and you have to get the right hormone chemistry for them and wait six months and you might get half of them to root. But figs are not like that at all. They're extremely easy. The critical thing with figs is the bottom heat. It really makes a difference.

 

Debbie Donley:

And so when you pot them up, you're potting them vertically?

 

Robert Dowell:

Yeah. You have to make sure that the part of that cutting that was closer to the base of the plant is the bottom. If you put the cutting upside down, the cutting might still root, but it will just be very confused and it'll take a very long time for it to grow the right way. The way I avoid confusion is I'll cut the bottom at a sharp slant and the top at a shallow slant, so the very pointy end is the down end.

 

Robert Dowell:

Figs are very interesting. They have a hollow pith, which can actually rot, and so that can compromise the health of your cutting. And so what we do is we dip the top part in like a hot wax just like the first inch or two of the cutting. And that just helps provide a little cap. A seal. A seal, exactly, so that water can roll off it. But the wax is biodegradable, so, in a few months it just dissolves.

 

Robert Dowell:

The fig cuttings, they're dormant hardwoods with no leaves. So they actually don't need that mist right away. We won't start introducing the mist until they start leafing out.

 

Debbie Donley:

So when will they leaf out?

 

Robert Dowell:

Usually in a couple weeks the bud, the buds will start to break. And it's always interesting because I have to watch them. They'll actually have tiny little figs trying to form on the cutting, and I have to pinch those off because I want the energy of the cutting to go into roots and leaves not figs.

Robert Dowell:

Fig is a huge genus. There's like 600 species of fig out there. And so we just grow the one common edible fig, but there's all sorts of tropical subtropical figs.

 

Peggy Cornett:

Jefferson apparently he did send a fig back from France, the Marseille fig, and uh, was his favorite fig. And the Marseille is a white fleshed fig, a very juicy fig. It never gets dark and brown like a brown Turkey. So that was one of his favorites.

 

Robert Dowell:

And that's true of green ischia of variety we also grow. It ripens a greenish yellow.

 

Peggy Cornett:

But the inside does get red though, doesn't it?

 

Robert Dowell: Yes, inside of the green ischia, it does turn sometimes a deep burgundy.

outside stays green.

 

Peggy Cornett:

Yeah. And, of course the way you know a fig is ripe is because it gets soft. You don't want to eat a green fig. It's not good.

 

Peggy Cornett:

The figs were being grown in an area of Monticello that Jefferson called the submural beds, which were beds below the vegetable garden wall, so that they could be more protected. So they were planted right up against the stone wall that was five to six feet tall.

 

Robert Dowell:

They can put on amazing growth too. Our figs at CHP can almost die to the ground some years, and they'll be seven feet tall by the end of August.

 

Peggy Cornett:

It's incredible. But if they do overwinter with small figs on them, sometimes those figs will ripen early, like in June, they call them a June fig and they can be really big on, and it's totally in a different time period from the when the fall fruits ripen.

 

8. Outro

Michael Tricomi:

Jefferson's passion for figs helped promote this fruit in Virginia and throughout the United States.

 

That's it for our January episode of “A Rich Spot of Earth.” Thanks for joining us. Stay warm and happy gardening!

 

Thomas Jefferson Center for Historic Plants

The Thomas Jefferson Center for Historic Plants, established at Monticello in 1986, collects, preserves, and distributes historic and native plant varieties and strives to promote greater appreciation for the origins and evolution of garden plants.

Sweet Acacia

Called by Jefferson "the most delicious flowering shrub in the world," he also felt that Sweet Acacia was "the only plant besides the Orange that I would take the trouble of nursing in a green house."

Geranium

Thomas Jefferson likely grew this species of Geranium in the President's House in Washington, DC.

Greenhouses

An in-depth look at Jefferson and greenhouses in the Thomas Jefferson Encyclopedia.

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