Happy First Frost Day!

Thanks to El Niño replacing his sister La Niña , we have enjoyed a delayed frost this fall, well beyond the average first frost day of September 14 for Calgary. We almost surpassed the extents of the Freezing Date Adjustment Factor Chart, with less than 10% probability of a frost this late!

Of interest to note is that the Average First Frost Day does not necessarily correspond with the Average End of Growing Season for perennial crops such as pastures and forages (see previous link for blow-up of map below). This map is based on an average daily temperature of less than 5°C after July 1.

This late frost is a good balance to our late Last Frost Day earlier this year, a welcome relief for many plant growers. I've heard some gardeners have even managed to grow corn this year, which can be hit and miss, depending on the location and variety of corn. Now to see how long the frost resistant kale and swiss chard hold out for!

Happy Last Frost Day (Sort Of)

Predicting the last frost day is always a gamble. As another food growing blogger writes, "tiny farming is in the end about a very natural, basic and satisfying form of gambling". For the Calgary area, the average last frost day is May 20. Since this year is below average in general, it is possible, if not likely, that the last frost day could be a week or two later.

Statistically the average last frost date represents a 50% chance that no frost will occur after that date. If you'd like to decrease (or increase) the risk of your plant investments, you can use the following Freezing Date Adjustment Factor (below):

According to this factor you can expect the chance of frost in Calgary after June 4 to be reduced to 10% (15 days after May 20). Note that the graph does not provide a 0% chance of frost after any particular date! According to Alberta government records, the Calgary area has seen as low as -2 C in July at least once in the last century.

The freedom from frost in this part of the world is no guarantee at any time. For the Middle Earth Garden this is not a large concern. Large parts of the garden can be covered if a frost is predicted. But of course frost is not always predictable. Hence the gamble. My investment is small, but for larger commercial growers this risk can be serious. This is where frost insurance comes in. For this garden, frost insurance is the local grocery store!

Agroclimatology - Growing-Degree Days

Today brings rain and sleet, with temperatures hovering around +1 °C. Rhubarb and other plant growth will be more or less paused for today.

Minimum temperature for plant growth is generally between 0 to 10 °C, depending on the plant. Some examples of minimum threshold temperatures for growth of some plants and insects (from here) include:

• 2.2 Spinach
• 4.4 Lettuce
• 5.0 General plant growth
• 6.0 Cabbage maggot
• 7.0 Potatoes
• 7.0 Variegated cutworm
• 10.0 Corn and beans
• 10.0 Grasshoppers, corn borers
• 15.0 General insect development

The minimum threshold temperature is used as the base temperature to calculate Growing-Degree Days. The Middle Earth Garden has about 1200 to 1350 total degree days above 5°C based on data recorded from 1971 to 2000 (see map below).

If anyone has more information on Growing-Degree Days (GDD) or related topics please feel free to share. I'm trying to find a chart of GDD for different vegetables but as yet unable to find anything.
The Lovage (above) came up after I dug the entire garden lightly with a shovel. I didn't realize it was perennial. Now I know! It came up shifted over somewhat from its former resting place, fortunately surviving the shovel abuse. Apparently Lovage is a good companion plant to almost all plants and considered a "magic bullet" of companion planting.

The rain barrels were drained dry after a temporary heat wave last Saturday and Sunday (+20 °C), watering freshly planted seeds including bush beans and spinach. The heat wave was caused by the locally well known chinook wind or less locally but more internationally well known föhn/foehn wind to be more meteorologically correct.

Today this gardener has retreated inside while the rain barrels refresh ready for the next change of winds.