I need a nerd!

[Hanau]

Who on here is good with numbers?

Take a look at this chart for Latah County:

http://www.cals.uidaho.edu/sandpoint/w_records.htm#LatahCounty

I'm trying to decipher the "Growing Degree Days" chart. What do the numbers mean and how do they add up?

[White Gardens]

It's just the average high and lows for each month.

The 2 in ten numbers or the 20% possibility that the temp will go above said number in a month over a ten year period.

Does that answer your question ?

[1993lx172]

The chart shows how many days in each month that where in the range of the corresponding temperature. For example from 1893-2005 there were only six days in January where the temperature reached or surpassed 40 degrees. And the numbers are then averaged together.

[Hanau]

That makes more sense. I was wondering how they got 810 days for August. It's an average over 100 years.

Thank you!

[Hanau]

http://www.extension.uidaho.edu/idahogardens/regions.htm

This is a cool website for any interested in landscaping in north Idaho.

We grow em fast and we grow em hardy.

[Richard Martin]

Growing Degree Days are simple. Everybody else that posted was just looking at the average. You need to scroll down a little to see the GDD.

If you look on the left side of the chart you'll see a base number. The first base number is 40. That is expressed in temperature degrees. If any particular day saw a mean temperature of 85 degrees then it is said that that day had a GDD of 45. The GDD is simply the difference between the mean temperature for the day and the base number. Mean temperature is simply the high and low for the day added together and divided by 2.

They are using average GDD for an entire month in those charts. So.... For August the GDD is 810. Divide that by the number of days in the month which is this case is 31 and you have an average daily GDD of 26. Add that to your base temp of 40 and you come up with a mean daily temp of 66°.

A more important temperature for a lawn service to use is the soil temperatures. If the ground is cold then grass and weeds don't grow or they grow very slowly. Crabgrass starts to grow at 55° and most lawn grasses grow at 60°.

[ALC-GregH]

A more important temperature for a lawn service to use is the soil temperatures. If the ground is cold then grass and weeds don't grow or they grow very slowly. Crabgrass starts to grow at 55° and most lawn grasses grow at 60°.

I though crabgrass needed 65+ degree soil temp to germinate?

[Runner]

Between 50 to 55 degree ambient soil temps (it's actually right around 53 degrees).