Monday, February 11, 2013

Understanding the Climate in Your Backyard

This post is part 2 in a 4 part series about weather and climate in the backyard farm.  If you missed the first article, you can get it here:

Weather and Climate for the Backyard Farmer

When you plan this year's garden, it's important to understand how the past climate can help you select your seeds and plants for the coming year.  One of the best ways to know whether a plant is likely to thrive is to talk with neighbors and other gardeners in your area.  Understanding climate terminology can better help you make informed choices about what you grow and what types of animals are likely to thrive in your backyard.

Thanks to modern technology, many of these resources are at our fingertips.  The most important thing to remember is that climatic averages are computed over a 30 year period, and are simply averages.  This means that the actual weather in a given year may shift dramatically from the average. Below are a list of some of the common climate information you can use in your planning. 

Frost Dates

Frost dates refer to the average date of the first and last frost in your area.   This means that if the last average frost is May 1st, that on average, half the time there will be a frost after this date and half the time the last frost is before this date.  If you are trying to determine when it is safe to plant crops outside, you can wait until the soil has warmed and you are clear of frosts, or if you are anxious to plant, you can wait until the average last frost date and look forward into the forecast to see the likelihood of another frost (remember that forecasters are often wrong and be careful with this approach).

Don't forget that since micro-climates exist around your backyard, and the first or last frost may not affect your entire garden.  If the frost occurs on a cold, clear night, you should be especially concerned about low lying area where cold air sinks.  Use coverings of some sort to protect plants, or water your garden liberally when an especially late or early frost threatens your crops.

Frost Free Season

This is the number of days between the average last frost and the average first frost.  You can use this information to grow frost sensitive crops that require a frost free season no greater than your frost free season.  If your average frost free season is 100 days, don't try to grow melons that require 130 frost free days.  You can often increase your frost free season by starting seeds indoors, using a greenhouse, or planting in cold frames.

Growing Degree Days (GDD)

The idea of growing degree days is slightly confusing since it refers to an accumulation of degree and not of days.  GDDs are the number of degree the average daily temperature exceeds 50 degrees over the year.  Put more simply, every time the average daily temperature (the average between the day's low and high) exceeds 50 degrees, the number of degrees are accumulate.  So if the average daily temperature for a given day is 59 degrees, 9 GDDs are accumulated.  Only days after March 1st with an average above 50 degrees are counted (degrees are never subtracted).  

While 50 degrees is the most common average used, some people will use different numbers based on the crop they are growing.  GDDs based on 50 degrees are commonly used to predict the the growth of trees and pests.  For example: a certain pest will emerge only when enough GDDs have accumulated in a given year.

While GDD can be confusing, it can actually offer a more insightful measure of when certain things will occur in your garden.  Since specific trees will flower only after a given amount of GDD, you can predict when in the year this will occur and whether your season is long enough to grow the fruit.  While hardiness zones are a wonderful tool, they are necessarily simplified.  For those looking to get deeper into their garden, exploring how GDD works can be incredibly beneficial.  If this seems like overkill, or simply too much - stick with the zones and you will be fine!

If you are trying to find GDD in your area, you can google it or try this sheet if you live in the northeast.  It is not a widely reported as hardiness zones, but is generally not too difficult to find.

Minimum and Maximum Temperature

While hardiness zones are based on the average minimum temperature, it is often helpful to know the lowest and hottest temperature your area is likely to experience.  If you live in an area that has cold temperatures in the winter with very little snow cover, you may have difficulty growing perennial plants from your zone and may need to go down a zone. 

Days of Sunshine

The number of days of sunshine is an important measurement especially for someone living in a region that experiences a large number of cloudy days. Even if your average minimum temperature puts you in a specific hardiness zone, many crops need full sun to thrive.  If your zone is a 6, but you have a large number of cloudy days (think Eastern Washington) you may need to plant crops that grow in a lower zone.

Hardiness Zones

Hardiness zones were developed by the USDA to serve as a quick reference for deciding which plants can withstand an average minimum temperature.  The zones range from 1 to 11 and are divided up into and a and b for each zone.  Most plants and seeds come with a range of zones.  While hardiness zones are very useful, they simplify climate and don't always reflect the most useful information.  Here are some of the problems with hardiness zones:
  •  Zones are based on average minimum temperature and don't take into account maximum temperatures, so areas with the same winter temperature and different summer temperatures will be in the same hardiness zone.
  • Regions with the same minimum temperatures may have drastically different overall climates.
  • Snow cover is not considered.  Since snow insulates the ground cold areas with snow cover will actually be in a warmer zone.
As long as you use the hardiness zone as a base and adjust for the micro-climates in your backyard, hardiness zones are very useful

Precipitation Data

Average monthly precipitation totals are useful when planning your garden.  By understanding how the averages change, you can plan when in the year you will need to increase your watering and when you are likely to experience larger amounts of precipitation and can store water.  Be cautious that large precipitation events (hurricanes, etc) may skew precipitation amounts.

You can find the data from a number of sources, but for the United States, I prefer the National Weather Service.  You can find climate data for your area by clicking on the map and than selecting the NOWDATA tab on the top right.

If you are just planning your garden for the first time, or are looking to refine your practices based on crop failures in the past, consider taking a closer look at the climate in your backyard.

Do you use any of the climate information above to plan your garden?

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