Adopt the pace of nature; her secret is patience. (R.W. Emerson)
I want to take a minute to talk about a little known and seldom used topic: Growing Degree Days (GDD). A new topic for many, or an old topic just called something else depending on where you live. We all know at least one piece of folksy garden wisdom such as putting down crabgrass preventative when the forsythia bloom. There are tons of little “tips” like this out there. Most of them actually based on science, even if most of us didn’t know it. So GDD is worth taking a minute to talk about.
So What are they?
Basically, they are a measure of heat accumulation to-date for the growing season. It is a tool used in phenology, which is basically the study of plant and animal life cycles. Tracking GDD allow you to predict plant, animal and insect development. These things are biologically timed to enter certain stages at certain times, often based on GDD. So forget about your calendar. Nature has it’s own, and it cares not for our man-made creations.
Growing degrees are calculated when the temperature goes above the base temperature, usually 10 °C. The actual formula is a little more complex because it requires taking into account the high and low temperatures. Then there are formulas for determining cumulative GDD, not just for a single day. The good news is , you don’t need to do math.
Why Use Them?
If you are a serious gardener, urban homesteader, or even someone just getting started, tracking GDD is something you need to consider. Why? Because as I mentioned earlier, nature keeps it’s own calendar. Some people may go out and do the same things at the same time every year, and get lucky as a result. But why not do things at the proper time, when conditions are optimal and you get the best results? From an integrated pest management and organic gardening standpoint, it’s worth it. Using GDD to time fertilizer and pesticide applications maximizes results. That saves you time, money and reduces chemical usage.
Getting it right the first time is important with plants. As many of us know, depending on what you are growing, you only get one chance to stop an infestation, block a fungus, or correct a nutrient deficiency. Watching your GDD, and knowing what is coming next can really give you an advantage.
Where Does One Get This Helpful Information?
I told you earlier, you won’t need to do math. You can if you want to, but there is an easier way. For those of us here in the states, it’s simple. Every county has an extension service , every state has its own friendly department of Agriculture who track this data for local farmers. But this data is just as helpful to the gardener as it is for the farmer.
This is the web page for the station nearest me, our local agricultural service has a monitoring station at a local apple farm. Here I use a “base 50” scale. Which calculates GDD using a base temperature of 50 degrees Fahrenheit:
I visit this page weekly through mid-season. They have some helpful guides as to what pokes it’s head up when. So I know when to start looking for certain pests. The best defense is when you know exactly what the offense is going to do.
So take advantage of the hard work others are doing. Most of it funded by your tax dollars anyway. You will be the local garden wizard who always seems to know what is going to happen before it actually does. Whether you choose to share your secret is up to you.