ISSUE 14  |  Less Is More

Urban Gardener: Is It OK to Reuse Potting Soil?

April 09, 2014 1:30 PM

BY Erin Boyle

Last weekend I wrested my window box from its perch and brought it into the apartment for a spring-inspired overhaul. My seedlings are progressing heroically, but it will be weeks before they’ll be ready to brave the outdoors–especially considering the snow that’s currently falling. In the meantime, I decided to pot some spring bulbs. But first I had to answer a basic container gardening question: Can I re-use last year’s potting soil? Or should I start fresh?

Photographs by Erin Boyle.

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The most basic answer is that yes, it’s possible to reuse last year’s soil. But first do a few things to perk it up–and replace its nutrients. Here’s how:

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First, remove any plant matter (roots, twigs, leaves) from last season. I plucked from the window box the dried up winter greens I had used to decorate it in January.

OK. ready to begin the soil remediation. Basic science tells us that plants use the nutrients in soil to grow. Over time, reusing the same potting soil in container gardening can deplete the nutrient stores in the soil and result in lackluster plants. Luckily, there’s no need to do a wholesale soil dump each spring.

To prep the box, I used a trowel to turn my soil. Turning the soil had the dual purpose of making sure that it wasn’t invested with bugs–in which case a dump might be worth it-–and making sure that the soil is light and fluffy. Hard and compacted soil doesn’t leave enough room for roots to grow, so this step is crucial. Use a sturdy trowel; mine is a DeWit Garden Hand Shovel ($25.90 from Kaufmann Mercantile).

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After I “tilled” my window box soil, I added a soil amendment. From a local shop, I bought a small bag of Plant-Tone Organic Plant Food (a 4-pound bag is $9.99 from Amazon). The mixture is an organic blend of bone meal, feather meal, poultry manure, and other stuff that smells a little funny but will return to the soil the nutrients that it might have lost. Alternately, you can add compost that you blend yourself at home or purchase from a farmer friend.

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I added about a cup and half of plant food to my soil and mix it well. This is definitely an occasion for breaking out the garden gloves: mine are Gardener’s Goat Skin Work Gloves, $32 from Womanswork. I knew that I’d be adding potted plants with fresh soil already attached to their roots, so at this stage I scooped out some of the old soil to make room.

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Over-wintering bulbs in window boxes in New York City is tough. Window boxes get much chillier than ground soil, which usually means that bulbs don’t survive the deep freeze of winter. Instead of planting bulbs in the fall, I purchased a few pots of Bridal Crown Daffodils from GRDN that had already been started. When they bloom, they’ll have ruffly white flowers with deep yellow centers; you can buy 15 bulbs Bridal Crown Daffodil bulbs for $11.01 from Holland Bulb Farms (available seasonally).

I gently separated some of the root bulbs from the mass to be able to fit them into my narrow box. Daffodil bulbs are hardy, so a little wriggling shouldn’t do any lasting damage.

I did the work on a backdrop of brown paper bags, opened up so that after I finished I could dump any leftover soil into my soil storage bag and not leave too much of a mess behind. I mounded the soilup and around my bulbs to protect them from the wintry start to spring we’ve been having.

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While a wide view outside of our window shows a scene that is still decidedly not spring-like, this little spot of green is a welcome reminder that spring is on its way.

This is an update of a post that originally published in our Belgium and Beyond issue on March 27, 2013.

Pests invading your potting soil? See Goodbye, Fungus Gnats: Pest-Free Potting Soil.

In a spring-cleaning frame of mind? See 10 Ways to Use Vinegar at Home on Remodelista.