Blossoms and spring frost.

Monday night and Tuesday night the temps were forecast in the high 20s. Apricot bloom is open and sweet cherry is very close to opening. The developing buds of tart cherry are still quite susceptible to freeze damage. (tight cluster developing buds will freeze more readily than the expanding blossoms). So I checked the temps every hour Monday night until 5am then went out to the orchard and started up the wind machines. We never really know if they help but it seems to be better than doing nothing. I watch 2 digital thermometers and I check the nearby MSU weather site report (hourly). When I think we are going to have an inversion freeze (frost) I start the 6 wind machines.

On clear calm nights in the spring the earth may radiate away its heat. When that happens the surface (buds, blossoms, etc) can lose their heat and be colder than the air. The air is then cooled, and as it becomes more dense it flows to the low areas. We place wind machines in low areas to displace this cold air and to draw in warmer air from up above. The idea is that then warmer air will be drawn down into the orchard as colder air is pushed out of the low spots. We have three wind machines powered with Chevy 350s and they run at almost full throttle. We have 3 diesels made from school buses. When all 6 are going we are gulping 40 or so gallons of fuel per hour! So I don’t run them until I am sure it is going to freeze.

On Monday night the temps hovered around 29 until 5am then it cleared a little and it dropped to 26. I started up the machines and it stayed below freezing until 7.30am.  On Tuesday the forecast was for even colder so I was watching the temps again. This time a breeze came up so there was no temperature inversion. It did not drop below 30 and I did not start the machines. Now we have a warming trend so I will catch up on sleep.

Incidentally, there was some damage to the tart cherry buds from Monday night. In the low areas many of the buds are damaged, and in the higher areas we can still find bad ons too. I don’t think it will be too significant, yet, however, Tuesday night the clouds cleared South of here and crops were damaged throughout Southern Michigan fruit growing areas. We will have to wait and see the economical impact of this.

John