THANKS TO YOUR BOUNTIFUL supply of Urgent Garden Questions, my friend Ken Druse and I are being kept busy. In our latest Q&A edition of my podcast, we’ll tackle how to plant groundcovers under established trees, and the gentle care required. Our other topics include what to do with that gift plant like a Primula, after you enjoy it for a week or two as a centerpiece, and how to use “pea brush” to “brush up” floppy plantings.

Ken Druse needs no introduction, but I’ll offer one anyhow. He’s a longtime friend and prolific garden author and photographer with hit books like “Making More Plants” and “The New Shade Garden,” and “Natural Companions.” Plus, he makes me laugh, which is very important.

Read along as you listen to the March 18, 2019 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).

early spring garden q&a with ken druse

Q. Hi, Ken.

A. Hi Margaret. You make me laugh, too.

Q. O.K., good; I’m glad it’s mutual. I was thinking maybe before we get started with this month’s questions, we ask the audience for a different kind of Urgent Garden Question for next month’s show. Because in April, to celebrate my all new version of the book “A Way To Garden” coming out 21 years later after the first one, you are going to host this show and interview me, right? [Laughter.]

A. Oh, yes. Right. Congratulations.

Q. I was thinking we should ask everyone and we’ll ask on Facebook and everywhere else as well, and on the blog. We should ask them what they want you to try to pry out of me, don’t you think?

A. Mm-hmm, yes.

Q. So not just your questions, but their questions. That’s the task audience: What do you want to know about Margaret—I mean, within reason.

A. [Laughter.] Really.

Q. That ought to be a real show to remember. Don’t miss it folks, and also a real show to embarrass, but let’s say we get on with the current crop of questions and answers.

A. Hit me.

how to ask margaret a question for the next show

TO ASK MARGARET a question for the April 2019 show, when Ken will host the program and interview her to celebrate her new book, just type your query into the comments box at the bottom of this story. Thanks!

can I plant florist primroses outside now?

Q. Lindley asks, she says the local shop, she’s in Connecticut, is selling primroses now. They’re already blooming, the weather will be below freezing in nights, and no better than 40 during the day. Can she plant outside now? Could you leave it in the garage? It’s like 40 degrees in there with some sunlight on them, keep them in the house till it’s warmer to plant outside?

She also says they’re selling Hypoestes, same questions as the above.

About these, like gift plants, floral types of plants, especially, and showy foliage plants, what do we do with them when we’re lured into bringing them home now?

A. That’s a lot of questions.

Q. O.K., sorry, tease it apart.

A. Well, what we see now are those sort of low-growing primroses and the come in several colors. I like the yellow ones because they smell. They have a wonderful fragrance and the other ones don’t really have a fragrance. [Above, a yellow polyantha type of primrose that was planted outside. Photo credit: By Meneerke Bloem – Own work, CC BY-SA 3.0.]

Q. Oh, interesting.

A. But keeping them going until the weather warms at least a bit, maybe for her at the beginning of May, end of April, that’d be great. I think if she has a garage at 40 degrees, and it has light, maybe sunlight, that sounds pretty good. But as long as you can keep it alive inside, you can plant them outdoors.

And sometimes they live quite well. Sometimes they live for a couple of years and bloom again, and then they just disappear. It’s funny because I’ve done some research on these and most people don’t exactly know what they are. Some people say that they’re Primula acaulis hybrids, and some people say they’re polyantha or polyanthus, so we don’t exactly know. But that they’re fun, and they’re not that expensive.

I’ve seen people put them in window boxes in warmer climates, not our climate. But yes, that’s a cool thing and she can definitely do it.

Now the Hypoestes, is that’s a tropical plant? [Below, photo by Forest & Kim Starr from Wikimedia.]

Q. I think that’s like a Zone 10 or 11 plant, so that’s clearly not going outside until summertime, if you want to use it in your pots outside.

A. They call that polka dot?

Q. Polka dot plant, yes.

A. But those are different stories. Well, that’s an indoor plant, really.

Q. Yes. It’s a “houseplant.”

A. And not bad a terrarium.

Q. Yes. I mean, theoretically you could use the primulas for a while in your house, enjoy them on the dinner table or whatever. and then get them out to a cooler spot. I mean, you could bring them in for a while as long as they don’t dry up and crisp up, right? I mean, couldn’t she?

A. Right, and the flowers aren’t going to last forever, but will last a long time. So probably by the time it’s time to put them outdoors, they won’t be flowering anymore.

Q. Right, but we’re not putting them outdoors in Zone 5-ish something in Connecticut, or even 6. We’re not doing that right now. We’re waiting till-

A. Maybe she should buy 10 and try them all over some outdoors, and then we could learn something on their demise. [Laughter.]

Q. Oh dear. All right.

planting in tree root zones

Q. Pamela saw a video on my website. I have a video [above], I think I call it “Making Mosaics,” and it’s kind of about under planting beneath trees and shrubs. This is a really good topic because before we know it, it will be spring everywhere. I mean, spring is already kind of rolling up the South, a little bit, and people are getting outside and during their garden cleanup, and they’re going to want to divide things and start planting and buy things and start planting them.

She said, when she saw this underplanting video, she had this question she said: “Your lovely and encouraging video makes me want to plant, plant, plant. However, I’m somewhat uncomfortable planting around established trees. The ground is so dense, and I’m afraid of damaging the root systems. Any thoughts to pass along as to how to underplant?”

So she has a good instinct that you don’t take out a giant long-handled shovel and start digging big holes, right?

A. You are correct. [Laughter.] I’m gulping here. It depends to a certain extent on what the trees are. If you can see the roots, if it’s like a shallow-rooted maple or beech tree, you really have to be careful and in those situations-

Q. Magnolias—a a lot of them have surface roots, even, you know?

A. Right, right. So if you really want something under them, it’s a good place for containers in shade, because you can make a container garden. I usually put down three bricks that aren’t on the roots, so you can usually see the roots, and then put an elevated container, either with annuals or even with hardy plants. But that doesn’t answer all the questions.

Q. Wait, now, the bricks are sort of like a shim underneath, like a supporting mechanism, and then you’d put your pots, so the pots aren’t just on the ground?

A. Right, and you’ll also have a little bit of air circulation, and the pots drain. Or a half whiskey barrel.

Q. So you could stage like a vignette in that area without being on top of surface roots that are obvious. That’s one way, but that’s not planting perennial things under.

A. I know what you would do, you would summer your houseplants there and they would look great.

Q. Yes.

A. However, I have planted under trees in a couple of different ways.

Q. Me, too.

A. And one way was to … In one area, I have a woodland garden and I made the woodland garden under a very tall, old white pine. If you think of the area under the tree as a big disk or circle, I made kind of a wedge shape, like a pie wedge-shaped bed [above, Ken’s diagram of the bed]. And the way I did it was put very coarse gravel directly over that small area on the roots, and then some soil mixed with compost—only about 3 or 4 inches. And I planted some wildflowers. In the first year I had a soaker hose, so they really got established, and that’s how I made that woodland garden and it’s doing fine.

Q. Can I ask a question before you continue? You said wildflowers, so what were these things they were in—3-inch inch pots? Were they tiny divisions, what were they? What did they kind of look like? They were not 2-gallon pots, whatever, right?

A. No, they weren’t, and that’s a good point because one thing you can do is you can get plugs, and now people sell plugs. Plugs are like, if you have a plant with cells, and they’re small plants. I didn’t do heucheras. I did different things like trillium and bloodroot from dormant parts of the plant, and you can do bulbs that way, too.

You might do Virginia bluebells from a plug [above, Mertensia virginica at Margaret’s], and those are pretty small rootballed plants, and it’s surprising they really get going almost as fast as some of the gallon plants. I took a dibble [below, Ken’s tool of choice], you know what that is, like a pointed stick or a very small trowel, and in some cases I mixed some soil with the hydrated water-absorbing crystals. I pre-hydrated them and mixed them with soil and put them in a little hole with a little plant, just to hold some moisture. Maybe this is getting too esoteric, but-

Q. No, no. We know you’re a little nutty, but that’s O.K.

A. Yes, if you can see the roots even you can make a little … stab, a little hole carefully in between the roots; just go back and forth. I suppose you could do it with a screwdriver, and then pop in a tiny bulb or a small plant in the fall, or you could even put seeds in the holes and start that way, or a dormant part of a bloodroot, something like that that is a little rhizome, and that would be done.

Q. I think this is really the key, whatever you’re using, it should be the least-intrusive version of that thing, a small piece or even a seed, a minor bulb, whatever. It’s almost like little pocket planting, like you’re just taking a tablespoon-sized hole here, and that kind of thing. The thing that’s a little bit confusing about it visually is that then when you step back, when you’ve done this, you step back and it’s like these little tiny polka dots spaced the appropriate space apart. It could be 6 or 8 inches, or it could be a foot apart, depending on what you’re planting. And it doesn’t look like much. In fact, it’s mostly a big bed full of mulch.

But as you just alluded to, those babies … not only will the roots of the tree thank you for not being aggressive, but the babies, the tiny little things [below, “plugs” laid out to plant under an old apple], will take off better too because you didn’t ask a big pot-bound perennial that you just bought for $20 to be shoved into a hole where there’s a lot of competition among an established root system, right?

A. Right. Competition for moisture.

Q. Yes, so rather than making anybody suffer, either the new things or the old things, it’s like these little tiny added … and you said like a dibble/dibber tool or sometimes even just use a tablespoon, a very narrow trowel, one of those tiny little trials.

The first time I ever did this, I didn’t know this was what I was supposed to do but someone sent me a flat of what you just said, plugs or liners, baby perennials, in the mail. It was Charles Price, Glenn Withey and Charles Price out in Seattle—Withey-Price Landscape and Design. Great garden designers and great plantsmen,  and they were working, especially Charles, on breeding hellebores.

He was crossing hellebores, the orientalis types, the hybrid hellebores. He was crossing different colors, and he sent me a flat of … He didn’t know exactly what they would be when they reached flowering age. They were small, it was like a flat of like, maybe 72..

A. Ooh!

Q. Yes, so they were small. It was a big flat, a big nursery flat, but they were small. It looked totally ludicrous after I did it.

A. [Laughter.]

Q. I put them under an old apple tree, and again, I wouldn’t want to hurt the century-old apple tree, or more than a century old. It looked stupid, and I put some trillium like you said, I had some trillium, I divided up one of my clumps of trillium—which you and I learned to do together, remember? [Above, rhizomes of trilliums in flower, out of the ground for moving at Margaret’s.]

A. Yes.

Q. Speaking of that, how did we … like with those little things like bloodroot and trillium, when do we do that? Like if we have it in our yard and we want to spread it around under other trees and these little divisions, when do you do that?

A. I want to ask you a question, too. You said you stepped back and you looked at mulch?

Q. [Laughter.] Yes.

A. Well, we don’t want people covering roots with a whole lot of awful bark or anything.

Q. No, but I do use a good quality of very fine-textured mulch. Not very fine like compost-fine, but it’s a decayed sort of, composted, stable bedding product [above]. It’s somewhere between shavings and very small chips, but it’s been well, well, well aged. It’s really great for just an inch or so on top of a new plantings, and it’s got some nutrients from the animal wastes and stuff. [Read Margaret’s Mulch FAQs.]

A. Well, when we were in Massachusetts, and we met Evelyn Adams and she had been dividing her trillium for 50 years. And she had easily 1,000, she divided them in flower in the spring, and I was horrified.

Q. Right, we thought she was going to kill them. But-

A. [Laughter.] I’ve been doing it ever since, and it works. Because it’s hard to find them when they go dormant. [How to divide trillium. Other easy-to-propagate wildflowers for shade.]

But with bloodroot, I think when the leaves are yellowing, you might dig them up then because they’re so easy to see. If you know where they are, you could dig them up in the spring, too before they have any new growth. And when you dig them up, you’ll find this rhizome that’s like a finger sort of. And as long as each piece has at least one growing eye—with bloodroot it’s so easy. You just either snap them apart, or cut them apart and plant those little pieces.

Q. No big shovels under established woody-plant root systems, and no deep addition of soil or mulch on top of roots, which can cause some sort of suffocation, can cause problems. We’re not doing either one of those things.

We’re working with the smallest possible plants—whether their baby plants that you buy, you ask your garden center, you say, “I’m doing this project, I don’t want the big perennial, but can you get me the little version of it?” Because they buy them in, in the spring to pot on themselves. And you’ll pay a premium. You’re not trying to get it for the wholesale price, but ask them to surcharge you and double the price or whatever, but give you that tray of 24 of something or 36 of something, or whatever it is.

A. I’ve noticed that some mail-order companies are actually selling those now, companies that used to be wholesale only.

Q. Yes, so look for that, or whether it’s tiny bulbs or seeds or whatever it is. And make some divisions from things as I say, sort of “shop in your own garden” in early spring, looking for little self-sowns.

That’s what I’ve also done, is like those hellebores that Charles sent me all those years ago that ended up teaching me about this underplanting method. They have had a billion baby seedlings since, and I’ve done all my other apple trees. There are five big old apple trees.

A. Oh, wow.

Q. Do you know what I mean? I take out the little seedlings that look like the ones that I was gifted all those years ago, but they are now offspring of my current ones. Anyway, and I continue the success. It’s not going to look good right away, it’s not instant gratification.

A. And water the first year.

Q. Absolutely. Anyway, so that’s a long answer, but Pamela-

A. I was interested.

Q. Yes, Marietta O’Byrne at Northwest Garden Nursery–she calls it “tapestry gardening” and I call it “making mosaics,” kind of planting little things under the woodies canopy and …

A. Polka dot planting.

Q. Polka dot planting. Well, that sounds pretty bad. [Laughter.]

…for more information on underplanting

• Making mosaics: Margaret’s version of underplanting, step by step.
• How to divide trillium.
• How to divide other spring shade wildflowers.
• Tapestry gardening with Marietta O’Byrne.

‘brushing up’ with ‘pea brush’

Q. Here’s another question, Ken: I linked to an older interview in something recent, an older interview with a flower gardener not long ago, in which she was talking about how sort of she was “underpinning an annual planting,” an annual that might get a little floppy otherwise. She was “underpinning it,” she said, “with brush,” to keep things from getting floppy.

Sharon and a couple of other readers were like, “What is underpinning? What does that mean? What is this brush thing?”

Now, I know it is a practice called brushing up or using a pea brush or whatever, but nobody apparently had heard of that, or among the readers, quite a number hadn’t heard of that. Did you know that Robert Frost in 1920 wrote a poem called “Pea Brush”?

A. No, but I use pea sticks to brush up.

Q. Apparently in 1920, it was the thing, so much so that Robert Frost wrote a whole … And he talks about:

“I walked down alone Sunday after church/To the place where John had been cutting trees/To see for myself about the birch/He said I could have to bush my peas.”

So making them bushy, using birch twigs that his neighbor John had pruned off something. And he goes on, and he talks about how this is going to be the support for the plants to come, and that there were birch boughs everywhere from this pruning job. And he came, and he took the bits that he needed. Yes, apparently it was the thing, but so when have you done it?

Pea Brush

By Robert Frost

I walked down alone Sunday after church
To the place where John has been cutting trees
To see for myself about the birch
He said I could have to bush my peas.

The sun in the new-cut narrow gap
Was hot enough for the first of May,
And stifling hot with the odor of sap
From stumps still bleeding their life away.

The frogs that were peeping a thousand shrill
Wherever the ground was low and wet,
The minute they heard my step went still
To watch me and see what I came to get.

Birch boughs enough piled everywhere!—
All fresh and sound from the recent axe.
Time someone came with cart and pair
And got them off the wild flower’s backs.

They might be good for garden things
To curl a little finger round,
The same as you seize cat’s-cradle strings,
And lift themselves up off the ground.

Small good to anything growing wild,
They were crooking many a trillium
That had budded before the boughs were piled
And since it was coming up had to come.

A. Well, this time of year, when I’m cleaning up or pruning things, I try to get the twiggy growth at least 2 feet long. You know, the tips, the ends of branches—and I try to save, well, I do save them in a dry place. Because when things flop over, sometimes you want to prop them up. And you can’t really stake them. It’s hard.

Pea is a good example because it’s just a vine that’s going to flop over. I put my arm under the floppy part, and lift it up with one arm, and then stick a dry, twiggy, brushy thing under it and let it flop back down and it holds it up. Sometimes I can make a little hole in the ground and the stem of that twiggy part will go into the ground, so it becomes like a shrubby stake, and you really don’t see it. It’s amazing. That’s called brushing up. The hardest thing is to make sure I remember to save all those twiggy parts.

Q.That’s the thing and it’s not ones that are just a single stick, shape like a stake, like just a straight twig. It’s the brushy ones like in the Robert Frost poem “Pea Brush,” and he’s talking about birch, which is a great one, because it does that. It divides; the fingers of the branch divide, and divide and divide.

When you take those and you stick the main stem down into the ground firmly, the brushy part is sticking up and it makes this armature, I guess, you could say, if you put that all the way down the row of say, ‘Sugar Ann’ peas, which are not super tall, but could use a little support anyway, or even slightly taller ones, it’s great for that. And I think that’s where it got, obviously, it got the name from that practice, but it’s less formal.

A. Sometimes you walk around and the snow’s knocked some little branches off and twigs, and you clean them up and throw them out. Don’t throw them out if they’re a good 2 feet long. And those are usually the twiggy one, and even some maple things fall down.

Q. Right. If you have this particular interview that was being referred to, I think it was even some of the zinnias that are … I don’t remember the names of the varieties, but they’re a little more floppy and loose. They’re not the big upright cutting kind of ones, and they have the smaller flowers. The idea was by the end of the season, they could be kind of messy, but if you put a little bit of this brush in, it’s not formal, like trying to stake it up and tie it to a stake. It’s not like that, that wouldn’t be appropriate.

It’s a little looser version of support, it’s kind of cool. And yet again, it didn’t resonate with people. It’s one of those things, a word or an idea that’s been kind of lost, I think, a little bit.

shrubs for privacy screening

Q. One quick question to finish up, from a gardener on the New Jersey-Pennsylvania border, so not those far from you, actually. She wants to create a screen to block a view into a neighbor’s yard, preferably something that includes some flowering, so we’re talking Zone 6-ish, and really, it’s to block a view.

I mean, my first question always when people ask me this, which is a common question is, do you have dear pressure?

A. Oh, my goodness.

Q. Because I mean, a long row of something that is available to Bambi is for me, it’s like, O.K., you’re down to almost no choices. You know what I mean?

A. Right, exactly.

Q. Yes. That’s a whole another… but let’s assume she doesn’t, and we have more choices. Any thoughts that come to mind?

A. Well, the first question, I was thinking is deciduous or evergreen? But I guess if it’s a screen, she really wants it to be evergreen if possible. Where she is, depending on if she’s got, and she probably does have kind of acidic soil, I would start with the native rhododendron, the rose-bay, I think it’s called. That’s a flowering shrub and a big shrub. It gets quite big, and it’s evergreen and it’s native, which is nice.

I grow Magnolia grandiflora [above, foliage detail at Ken’s], and people always say, “No, you can’t grow that. That’s a Southern magnolia.” I’m in a cold Zone 5, you’re in Zone 5, I think.

Q. Yes, 5B.

A. And I grow ‘Edith Bogue,’ which is a variety of … I grow several Magnolia grandiflora, it’s an evergreen Southern magnolia, but ‘Edith Bogue’ is right on the road. She gets splashed with salt spray in the winter, it’s gone down below zero. She blooms in the summer. It’s not as much bloom as I would like, because it’s in shade. And if you prune, she’ll keep her branches all the way to the ground. And that’s quite something, I think. I don’t know if deer browse those plants.

Q. ‘Little Gem’ is another one of those, isn’t it?

A. Well, ‘Little Gem’ isn’t as hardy.

Q. I see, O.K.

A. ‘Bracken’s Brown Beauty’ is the small-leafed one that’s like ‘Little Gem.’ It’s beautiful, but also some … like one out of every four winters, it gets pretty ratty looking. It gets damaged, but then it comes right back. But ‘Edith Bogue,’ it laughs at the snow and the cold.

Q. All right, so that’s one thing that you like, if you want some evergreen cover, that’s a little unusual or two things that you like. One thing I’ll say in the last minute is just that, again, you’re reminding me of Evelyn Adams and when we learned to divide trilliums when they’re in bloom. And when we were working on that book, that book of yours, you were kind enough to take me with you on some of the visits to exceptional gardens that you were doing for “The Natural Habitat Garden” book all those years ago.

And I went along, tagged along, and it was … I think we sort of coined a phrase like “biohedge.” In other words, not just one plant, like 50 of one plant stretching the whole length that you want to block, but like a mix of things for different interest for the beneficial insects and birds and animals and stuff like that.

With that as the last word, I will say, Ken Druse, thank you very much. I’m a little nervous about next month, but I’m looking forward to talking to you. I’ll talk to you soon.

A. [Laughter.] I can’t wait to see your new book. I can’t wait.

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 10th year in March 2019. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 18, 2019 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).