Sneak peek

Something big is being planned!  

I can't say anything quite yet, but here's a peek at what I'm working on. 

(It really is just a peek - I'm not giving anything away yet!)

How I use growing degree units

A few weeks ago I described how to calculated growing degree units.  Remember?  Basically they are a measure of heat accumulation, and pretty useful when you're dealing with changing seasons, night and day, or greenhouses heated to different temperatures.  Here's how I use them.

We'll use lettuce as an example.  I planted lettuce nine time throughout the fall last year.  Using all the growth rate data I collected I figured out how many days it took to reach 8 cm. (8cm is a good baby green size.)  In the graph below you can see that it took more days to reach 8cm as the season changed from fall to winter, especially in the cooler greenhouse.

Still on board?

I did the same thing, but changed growing degree units for days.  So, I calculated how many growing degree units it took for the lettuce to reach 8cm.  The number of growing degree units accumulated by lettuce at 8cm stayed about the same in the warmer greenhouse and slightly decreased in the cooler greenhouse - even though the actual amount of time to reach this size increased.  Make sense?

So, now on to interpretation.  Why does this happen and what does it mean?  I'm not totally sure yet, but here are some ideas:

• It takes about 600 GDU to have a harvestable baby lettuce crop.  How long it takes to accumulate that heat can vary. 
• Why does the number of GDU decrease in the cooler greenhouse?  Maybe because there is so little light late in the fall.  Even if greens were in a warm environment, their growth would be limited due to limited light.  

* As usual, this data pertains only to our greenhouses this fall.  It is not complete and should not be used elsewhere.  If you are looking for complete data pertaining to winter greens growth, and growing degree units you'll just have to wait until I'm done with my thesis! *

What I'm eating today - the first harvest of the year

Yesterday I harvested the first greens of the year.  I planted the mizuna a month ago and the handful I harvested was just enough to cover a pizza.  

Corvair spinach

I have been tired out for the past week, despite two greenhouses filling up with cheerful, green seedlings. After a week long blogging break I am back!

Much of what I'm doing this spring is a repeat of last fall's experiments.  The major difference is the new spinach variety, corvair, which is resistant to 11 strains of powdery mildew.  The first true leaves have started to emerge and already I am in love.  Corvair has much rounder, upright leaves than space.  These were major selling points when I was deciding what variety of spinach to use.  Sunny days keep the greenhouses between 60 and 70 degrees, which is pretty nice to work in.

Baby brassicas

The brassica's are growing despite the cold and dark.  Tokyo bekana plugs are in the back ground and pak choi is in the foreground.

What happens when the media is frozen:

You have to use a pick ax to get it out. 

What are growing degree units?

Last week I teased you about growing degree days.  Weren't you intrigued and just dying to know more?  Probably not, but that doesn't matter because you're going to find out.

Let's start with the problem.  I have two greenhouses set at different temperatures.  I also planted greens on different dates throughout the fall.  In the chart above you can see:

1. The average temperatures were different in the two greenhouses, especially as it got cooler
2. The temperatures vary depending what time of the season greens are planted 

This is where growing degree units come in!  But what are they?

"Growing degree units are a measure of heat accumulation used by horticulturists, gardeners, and farmers to predict plant and pest development rates such as the date that a flower will bloom or a crop reach maturity."  Wikipedia 

So, they measure heat accumulation.  Luckily they are easy to calculate, you just need to know:

1. Average daily temperature
2. The base temperature, below which your plants won't grow.  For salad greens I use 40 degrees F.  This is called the biofix.

With these two things, and the date you can calculate the number of growing degree units in a table like the one below.  All you do is subtract the biofix from the average daily temperature. The difference is the number of growing degree units accumulated that day.  Then you can add them up over a period of time (like a growing season) and compare differences in temperature!

These two tables show the number of growing degree units accumulated in each greenhouse over a ten day period.  Greenhouse 2, the warmer one, accumulated nearly twice as many growing degree units in this time!

Growing degree units are used to predict flowering blooming, crop maturity or insect emergence.  I've been using them to examine the growth rate data, but more on that in the future

Source

"If you eat, you're in"

Source - which is worth visiting to read the comments.

First spinach seedlings of the new year!

I was going to write about growing degree days, but who wants to read about that on a Friday?  Plus, the spinach I planted ten days ago is sprouting!  After the trama last fall seeing these new spinach plants has cheered me right up.  So has this little guy:

Last week I knocked over some lettuce seeds into a tray.  They were too wet and dirty to plant with the vacuum seeder, so I stuffed them in a little pot.