GROWING DEGREE DAY UNITS

 By Ginger Baer, Gilpin County Master Gardener

I have been gardening for over 50 years. I became a Master Gardener in Gilpin County in 2016. I participated in growing a variety of vegetables in our Community Garden for these past 5 years. All I can say about this year is that my garden was mostly a failure. Of course! It is 2020.

This led me to wonder why things went so bad this year.  I grew almost the same types of vegetables this year that I had done in the past. I decided to dive into Growing Degree Day Units (GDU), because I felt that this year was unusually hot.  We have kept track of our high and low temperatures at my home for many years.  To that end I decided to create a spread sheet to track those GDUs.

The way to calculate your growing degree days is fairly simple.

In Gilpin County we use 50 degrees as the baseline. So an example of the calculation could look like this:                          [(79 + 45)/2] – 50 = 12 GDU

So what did I find out after 4 years of tracking?

I found that 2020 and 2018 were fairly similar and 2017 and 2019 were somewhat similar.

GDUs     2020 = 1720.5

               2019 = 1381.5

               2018 = 1742.0

               2017 = 1470.0

So how did these variations affect my crops? I generally grow the cold weather crops: lettuce, spinach, radishes, turnips, carrots, beets, broccoli, as well as moderate weather crops: summer squash and early tomatoes.

2017 was a pretty successful year. I was able to share greens with co-workers and had a really great summer squash year.

2018, even though it was a warm year, was a great year where everything seemed to flourish. Again, squash flourished as did some flowers for the pollinators.

I had no complaints for 2019, except it was a cold start. Snap peas, onions, squash, turnips and even a pepper!

So what was 2020 like?  I had a lot of greens in June. I went to plant a successive crop and even though the seeds sprouted, they did not take off.  I got some summer squash, but about half of the squash that set had blossom end rot.  To me that means uneven watering, and indeed 2020 was an extremely dry year.  I did get a successful crop of Early Girl Tomatoes.  However, as they were starting to ripen in early September, we had a snow storm.  I pulled the plants and let them ripen on the vine by hanging them upside down in the basement.

I also grew some experimental potatoes for CSU Extension. I planted them June 1 and harvested them around September 20. The crop was not very impressive. I only got about 4-5 potatoes for each plant and the potatoes themselves were really really small. I would say that the largest one was about 2 inches long.

So what did I learn from all of this tracking? Not as much as I had hoped. Keeping track of one year to the next helped me see that there are no two years the same. I also think, even though I hand watered everything every year, that 2020 was extremely dry. Keeping a journal of successes and failures is a good thing to do. I also think keeping track of moisture might be a good addition to this analysis.

Well now it is time to put 2020 gardening behind and start planning for a very successful 2021. Remember to order your seeds early!

For more information on growing degree units, take a look at CSU Extension Fact Sheet, Vegetable Gardening in the Mountains - https://extension.colostate.edu/docs/pubs/garden/07248.pdf