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Connecting urban gardeners with needed amendments

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This article comes from the NOFA/Massachusetts 2016 June Issue Newsletter

By Caro Roszell

Mineral blend distributed at Gardeners Gathering

Growing food in the city has many advantages. Concrete and buildings create a warm microclimate, allowing a longer season than for rural growers. Pest and disease pressure may also be lower, due to lower populations of wildlife and the absence of monoculture. Irrigation isn’t an issue for most urban gardens, as water access points are numerous. And many cities offer free or low-cost compost. Cities seeking to be greener have, at many junctures, facilitated municipal composting operations and offered the product to community gardens. In fact, the well-known Quebecoise farmer Jean-Martin Fortier has often claimed that, before the automobile replaced the horse-drawn carriage, Paris grew enough vegetables to supply all of the city’s hotels and restaurants using the composed manure cleaned from the city’s streets.

There is no doubt that high organic matter is beneficial for the soil ecosystem. However, as the careful soil student learns, compost is quite high in phosphorous (P) (and, to a lesser extent, potassium). Over time, repeated applications of compost can result in excessive levels of P, causing imbalances in plant growth.

Boston, like many other cities, historically has provided free or subsidized compost deliveries from municipal composting sites. As a result, many garden plots have received annual compost applications for ten, twenty-five, even forty years— gradually raising phosphorous without proportionally adding calcium, magnesium, and other trace minerals.

To make matters worse, most of the amendment blends available at garden stores proclaiming ‘balanced nutrition for vegetable crops’ are formulated for suburban or rural growers, providing N-P-K, which, with excessive P, will scarcely help the urban grower.

So, this year, NOFA board members and staff worked together to design a custom mineral mix, using nine ingredients from the Bulk Order, to specifically target and balance compost-heavy urban soils in quantities appropriate for the average community garden plot. The mix raises calcium in particular—a crucial but under-valued macronutrient—but also provides potassium, magnesium, nitrogen, sulfur, and trace minerals like boron and silica. This mix, of which over 200# was distributed at The Trustees of Reservations’ annual Gardeners Gathering event in March, will help growers to achieve higher yields of crops with a higher nutritive value, effectively increasing the nutritional value of a gardener’s hard work.

The response to the mix was enthusiastic, with the NOFA table flooded for hours with curious gardeners. With the right guidance, the average community garden can easily correct soil imbalances for just a few dollars per person (or plot) per year, by pitching in on 50# bags of amendments and then dividing up the bags among the gardeners. Going forward, we will be working hard to help Boston’s urban growers utilize the Bulk Order to help address soil mineral imbalances cheaply and efficiently, for better health and better yields.


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