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THE PUBLIC SPACE GARDENS OF CAPITOL HILL
The Tree Box Gets a Great Makeover

Spiraea, English daisy and sunfl ower share this tree box with a maple tree.
Spiraea, English daisy and sunfl ower share this tree box with a maple tree.

Most people agree that Washington is greener than other urban cities. Part of that is due to our trees; Washington has great trees. But another, rather large, contributing part of the green scene in Washington is the garden aficionado – Washingtonians love their gardens.

On Capitol Hill there are many great gardens, and on any given day during the year, a stroll through Capitol Hill can lead to endless sightings of meticulously maintained front yards. Never mind that in most Capitol Hill front yards the land is on loan to the homeowners from the city. This fact has not stopped Hill garden buffs from having wonderful lawns, formal and informal gardens, and even the occasional vegetable patch. During the last few years, the greatness of the “public” gardens of Capitol Hill has not been confined to just the loaned front yards; it has spilled over into the tree box areas. You know that strip of earth between the curb and the sidewalk intended to have some species of tree growing out of it? Well, these spaces have become the most wondrous, innovative tributes to the Hill and the great gardeners that live here. On a recent walk down Independence Avenue, I encountered blocks of overflowing, colorful, tree box gardens. Each garden seemed to outdo the last one with many species of plants represented. I felt a great sense of gratitude to all those anonymous gardeners who have taken the time to give to the street, block and city a great green gift.

The Plants

Daylilies and violets fill this tree box.
Daylilies and violets fill this tree box.
I was amazed as I started to catalogue the plants; the list was a far cry from the traditional and overused liriope and barberry. There were daylilies and monkshood, yucca and spiraea; roses collided with yarrow, nandina and hibiscus, junipers contained by sunflowers, and coneflower overgrowing into primrose. The overall themes in these gardens were one of full billowing cottage-cutting garden. There were many plants that were volunteers, like the rose campion I found growing in a small recess of a huge elm tree and the primroses that had started to spread into the cracks of the sidewalks. In one block, the four o’ clocks had whittled out a niche between the light post and curb. And on another street, the sunflowers were popping up beside a birdfeeder. These tree box gardens looked better than any year I can recall. Lush, full and fabulous.

Why So Beautiful?
The big reason for their success this year can be attributed to the way Mother Nature has agreed to help out the urban gardeners by giving us more than enough rain. Last year at this time, the calls that kept most landscape professionals afloat were from folks asking for help with their withered gardens. What a difference a year makes. Water has not been an issue, yet. So the public gardens have responded with great growth and blooms.

Your Very Own Public Garden
So how do you achieve a public garden of your own? Well, one thing these great tree-box gardens all have in common is that they were, obviously, well prepared. The following punch list will give you a great start at greatness for your block’s empty tree boxes.

  • Be mindful of the trees in the space. If the box you want to work in has a newly planted tree, check out the urban forestry website to gather info on the final size and span of the tree. Please be very careful when digging that you are not damaging the tree’s roots. And if you happen to be filling up an empty tree box only with plants, check with the city to see if that space is scheduled to have a tree planted there in the near future. The city will work with you to make your beautification plans work with theirs. 
  • Prep the soil. Let’s say you are working with a vacant tree box, soil amendment is the most important thing you can do. I suggest removing the top 6 inches of soil, adding a little pellet lime to help sweeten the soil, and then mixing in 50 percent of the old soil with compost. Some of the good commercial ones are Bumper crop and Compro. You can add about 4 percent coarse sand if the soil is dense and compacted. Add about 1 cubic foot of peat moss to help with water retention. And use a natural slow release fertilizer at about half strength as a top dress when planting the plants. Ask your local gardening center or a landscape specialist for help with these combinations.
  • Choose the plants. The plants you choose should be tough. Check the light and foot traffic and plan accordingly. Remember, this is a gift to the city, and not everyone understands how to be appreciative of gifts, so don’t plant large expensive plants in the space. Using trial and error and opting for the smaller plants at purchase will help to keep your angst down should some inattentive giant’s foot plow down one of your plants.
  • Fertilizer. You should err on the side of under-fertilizing since you are planting close to the city’s sewers. Try to use natural products and compost. See the section above on how to do it organically.
  • Water. When you plant this garden, be prepared to dedicate an hour a day to gently soak the ground. Do this for the first two to three weeks, then cut back watering to several times a week but continue to water deeply to ensure the plants form a deep root system. After the first season, you should be prepared to water weekly when nature does not provide at least an inch of water. When adding new plants, follow the daily water routine.