Soil, lead and containers

The most important thing to know about gardening in New York, and the thing least often said out loud.

Do not assume the ground is safe to grow food in. This is not alarmism and it is not rare — it is the default condition of urban soil in an old industrial city.

The problem

New York's soil carries the legacy of leaded petrol, lead paint from demolished buildings, coal ash, industrial activity and construction fill. Lead is the main concern, but it is not the only one.

Many community garden sites are former vacant lots, which frequently means former buildings — and the demolition rubble is still under the topsoil.

Lead is a particular problem for children and pregnant women, and it is taken up more by root vegetables and leafy greens than by fruiting crops like tomatoes.

Test before you plant

Soil testing is inexpensive and available through university extension programmes — Cornell operates a well-known soil testing service used widely by New York gardeners. Send a sample, get numbers back for lead and other metals along with fertility and pH.

Many established GreenThumb gardens have already been tested, and clean soil has been brought in. Ask. If nobody knows, test.

The solution: raised beds

The standard approach is to garden above the existing soil rather than in it:

• Build a raised bed at least twelve inches deep, deeper for root crops
• Lay landscape fabric or a barrier at the base to separate new soil from old
• Fill with clean imported soil and compost — GreenThumb supplies these to registered gardens
• Top up annually, since the level drops as organic matter breaks down

Containers work on the same principle and are the answer for balconies, roofs and fire escapes.

Sensible practice regardless

• Mulch bare soil so dust is not raised and tracked around
• Wash produce thoroughly — a good deal of contamination is soil on the surface rather than uptake into the plant
• Peel root vegetables grown in questionable soil
• Wash hands after gardening, and especially supervise children doing it
• Keep a path surface between beds so you are not walking bare ground

Compost

Composting on site closes the loop and improves structure enormously, and most community gardens run a communal system. Learn the garden's rules before adding anything — most exclude meat, dairy and cooked food, and a badly run bin is the fastest way to fall out with your neighbours.