The Trick of Adapting to Migrating Growing Zones
By: Violet Bee
Tags: Climate Change, Permaculture, Food, Agriculture, Environment

I was conversing with someone recently, about the American chestnut, and whether or not her growing zone would adjust enough in the next 20 years so that she’d be able to harvest nuts from the trees. Her current growing season is too short.

It’s a sad reality that all gardeners and farmers must consider, especially in the choice of crops and varieties. While there are some arguments for good news in longer growing seasons, especially for annuals, the added volatility that is expected as the climate continues to warm will challenge the most experienced among us.

Growing Zones

The growing zone map, as pictured here, results from the average extreme temperatures over a 30 year period.

A recent New York Times piece, contains a visual with predicted growing zones for 2040, which offers an idea of how we’ll all be affected and gives us some clues on where to start.

This is the 2040 prediction.

The growing zone is the most basic of the indicators in choosing perennials and the one most commonly followed.

Our challenge is that the growing zone map can’t keep pace with the changing climate. 30 years is a long time in a world of climate chaos and an average may lag considerably behind the northern migration of the zones. Taken alone, though, it’s not an insurmountable problem. The added complexities of frost dates and chill hours increase the risks of perennial crop loss.

Frost & Chill

Mast (nut and fruit) producing trees and all other deciduous shrubs and vines are sensitive to frost dates and require a certain amount of chill hours — commonly measured between 34 and 43 degrees Fahrenheit — to produce crops.

Too few chill hours and trees may have late leafing or uneven/no flowering. Any of those can mean no fruit or nuts. Too many chill hours and there’s a risk the trees will break dormancy before the end of the frost season and a frost can result in no fruit or even a dead tree.

Beyond the weather becoming more severe, the chances that it will become more erratic are the most alarming.

Since the hours below freezing are not factored into the chill hours, the long cold of winter, usually January-February where we’re located, are not in play. In the last few years, though, we’ve had odd weeks of above-freezing weather during what should be the coldest months of the year.

It likely wasn’t the two weeks of extreme cold that killed all of my peach and nectarine trees. It was the excess of chill hours that left them vulnerable to the last few frosts that came after they’d broken dormancy.

Small-Scale Agriculture

The most common methods of orchard growing and other plantings of tree and shrub crops are large mono-cultures, or at most, plantings of only a select few types/varieties. These leave us vulnerable to a host of problems, not least of which is crop-loss related to weather events.

Diversity

One of the primary principles of Permaculture systems is diversity. Depending on the text you choose, you’ll find it in various forms.

Emphasize Diversity on All Scales — Heather Jo Flores, Food Not Lawns: How to Turn Your Yard into a Garden and Your Neighborhood into a Community

— Heather Jo Flores, Food Not Lawns: How to Turn Your Yard into a Garden and Your Neighborhood into a Community Use and Value Diversity: “Don’t put all your eggs in one basket” — David Holmgren, Permaculture Principles and Pathways Beyond Sustainability

— David Holmgren, Permaculture Principles and Pathways Beyond Sustainability Preserve and Increase Biodiversity of all Types — Rosemary Morrow, Earth User’s Guide to Permaculture

For Permaculture, the value in diversity goes beyond erratic weather into areas of nutrient use and pest deterrence, among others, but adapting to a more volatile climate is enough reason to adopt a diverse approach in our plantings.

While the risk of tree loss always remains, like my peaches and nectarines, in many seasons it is more about maintaining a harvestable crop. By choosing to plant as many types and varieties of perennial crops as our zones will allow, we extend our flowering and pollinating windows and insulate ourselves against total loss.