Planting Combinations for Window Boxes

A South Brooklyn take on a Brooklyn Heights window box

Every time I go to Brooklyn Heights lately I keep getting sidetracked by those window boxes I recently posted about. They were pretty a couple of weeks ago, but they’re even prettier now—brighter and more colorful, all done up for April. The ranunculus are out, and the muscari, and the violas. In winter the boxes looked stately and elegant, but spring’s window boxes are so cheerful that I keep having to stop to take photos.

Photographing window boxes, or even really noticing window boxes, is not something I did much of before I moved to Brooklyn and became a city gardener. I think I saw them as a little bit old-fashioned—very much In Their Gardens, but not in a good way. Also, you know those window boxes you can buy from places like Lowes and Home Depot that come already planted? That’s what would come to mind. A less than exciting row of petunias or begonias, or pansies, if you’re lucky.

But the window boxes of Brooklyn Heights are something else. I already wrote about how most of them are designed by the same person, and how they’re also changed out every season so that they’re always looking their best and very of the moment. I’m not sure where the designers get their plants, but they must have so many to choose from, and unique ones, too.

Each box is a garden in itself. Some of them are tall and grand, and others are like little jewel boxes. Some are planted entirely in shades of green and make me think of imposing hedges in an English estate, while others are light and frilly, like tiny wildflower meadows. I try to take photos quickly—I don’t want it to look like I’m casing brownstones—and then back at home zoom in on the pictures to see all the plantings.

We don’t have any window boxes at our apartment. Our building isn’t a brownstone or particularly old, and there’s a window on our terrace, but it’s usually in the shade, and I’m not sure if the landlord would let us attach a box. There’s just a strip of the terrace—a few feet wide—that gets full sun, and that includes a wall that is pretty in a faded kind of way and just begging for a plant to crawl up it. A climbing rose or clematis would look beautiful, but, again, I’m don’t want to ask about drilling into the brick. But we do have a ledge that runs the entire length of the wall, and even though it’s a tiny bit slanted, I think window boxes might be a good solution for adding height and taking advantage of all that sun.

We bought four small-ish metal window boxes from Ikea—they’re meant for hanging over a railing, but we’re just using the boxes and not the frames. And the color—a pale blue/green—is almost the same color as the painted ledge they’ll be sitting upon. If I put little pot feet at the bottom of the boxes in front it may balance them out, and maybe they’ll stay put. I hope so, at least.

Our window boxes won’t be getting a makeover each season. I’m going for a mix of perennials and annuals that won’t mind full sun and a less than ideal watering situation. I doubt everything will be in flower at the same time, and I don’t know how long the plants will take to fill out the boxes, but it’s an exciting experiment, a first try at window box planting. If they don’t look so great, at least it will be only us who sees them and not the whole neighborhood.

I’m taking inspiration not just from the Brooklyn Heights window boxes, but also from the new Sarah Raven book I keep talking about. She doesn’t really write much about window boxes, but many of the concepts of container planting apply to both. The thriller/filler/spiller method isn’t unique to Sarah Raven—her thing is more of the bride, bridesmaid, and the gatecrasher formula, which I love. But she does cover both methods in her book, and I think the first might work better for planning a window box.

The ‘thriller’ is the most exciting/largest/tallest plant, or the star of the show. Sometimes it’s a tall ‘pillar,’ but not always. You could also call this the ‘bride.’ The ‘filler’ is very much like a filler flower in a bouquet—something that takes up space, adds some froth, but that also complements the ‘thriller.’ A very ‘bridesmaid’ role. No overshadowing! The ‘spiller’ is also self-explanatory: a plant that can delicately tumble out of and trail down the edges of the window box. Now, this isn’t the ‘gatecrasher,’ which, by Sarah’s definition, is more of an unexpected guest—maybe a plant that’s just a bit off. It doesn’t quite match the aesthetic of the rest of the plants, but it keeps the whole combination from looking too perfect, too tasteful.

I’m not sure if there are any gatecrashers in my window boxes. I didn’t invite them, at least, but they might show up anyway. I’m sure that a flower might bloom in a color that doesn’t fit in as well as I’d wanted it to, but hopefully it doesn’t cause any scenes. I have four boxes, and I tried to stick to plants I already have growing and perennials I overwintered from last year. I did buy a few perennials at the Gowanus Nursery pop-up sale a few weeks back specifically for the boxes, so I’m thinking I should be set. Now I just have to finish hardening off the annuals, and once we get holes drilled in the bottoms of the boxes I can start planting.

My window box lineup of plants

Thrillers

• Agastache ‘Purple Haze:’ This was the first perennial I bought last year when I was in South Carolina. I went to a nursery planning on buying an annual, but I didn’t like any of them, and the perennials were just a dollar more and much better looking, so I got this one. I love a good flower spike, and this agastache grows up to 24-36 inches, so it’s a good pillar, too.

• Gaura ‘Whirling Butterflies:’ This was the next SC perennial I bought because my seedlings were so slow-growing and I needed some instant color. I’m not sure if this is the variety I have, but it’s close. Honestly a bit filler-like, but it does grow tall, topping of at around 36 inches. There’s a chance it didn’t pull through the winter—I still can’t tell—but if it does it will probably go in one of the window boxes.

• Calamintha ‘Montrose White:’ Maybe I need to re-think this one for using as a thriller/pillar since it only gets up to around a foot high, but I bought it at the Gowanus Nursery pop-up sale since it seems like a good pick for a window box, water demands-wise.

• Agastache ‘Kudos Ambrosia:’ And yet another one I bought in SC. I didn’t need another agastache, but the colors were so pretty and the bees just loved it. This one gets to around 18 inches, so not terribly high.

Fillers

• Cosmos ‘Rubinato:’ I love cosmos for filling out a space in a flower bed, so even though this one is on the tall side for a filler (around 2 feet) I’m going for it. It’s still short for a cosmos.

• Scented Geranium ‘Attar of Roses:’ I have two cuttings on the propagation shelf right now and I think that they’re taking root. I really hope they do because I think they’ll be great for a window box since they don’t get too thirsty or need too large of a space to live in.

Spillers

• Origanum ‘Amethyst Falls:’ I bought two of these at the pop-up sale because I love their weird look—kind of like hops, but purple—and how they hang down heavily off the edges of planters.

• Nasturtium `Purple Emperor:’ At the Gowanus Whole Foods there’s a rack of Botanical Interests seeds placed dangerously near the checkout, and I bought these on a whim, thinking I might find a hanging basket for them. I’m hoping they’ll spill out of window boxes instead.

One of the Ikea window boxes and some of the seedlings—not planted yet, but I’m thinking maybe four plants per box will work?

Garden Notes:

• Starting to harden off the zinnias and nasturtiums so that they can live outside, too. My seedlings always look so much healthier once I get them out into the cold frames—I don’t know if it’s the apartment humidity or the grow lights, but the plants aren’t loving it inside so far.

• Pretty sure I can get most of the tender annuals planted this weekend! After tonight the nighttime lows will be in the 50s and above, so I might take my chances and plant out the dahlias and cosmos and zinnias.