Weather Trends and How To Use Them To Your Advantage In The Vegetable Garden

After all the crazy wet weather we’ve been having here in SW Washington lately, I thought gardeners might be interested in some weather trends that will help you know when to plant certain types of vegetables outdoors safely.  Let me start by saying my information is for my particular micro-climate found in an urban garden that tends to trend a little warmer than normal due to close proximity of houses, fencing and all of the concrete and asphalt nearby; if you live at a higher elevation than 305 feet above sea level, then you will want to take that into account as you plan your garden, because you may have different weather conditions where you are at.

These are a few quick records: 

2008 stats:

  • last killing frost in spring:  March 31st
  • first killing frost in fall:  December 14th
  • frost-free days:  257
  • air temperature reliably above 40 degrees at night:  May 1st
  • air temperature reliably above 45 degrees at night:  May 12th
  • air temperature reliably above 50 degrees at night:  June 26th
  • air temperature reliably above 55 degrees at night:  Never (*This was an unusually cold year.)
  • air temperature reliably above 60 degrees at night:  Never emphasized

2009 stats:

  • last killing frost in spring:  March 12th
  • first killing frost in fall:  December 3rd
  • frost-free days:  265
  • air temperature reliably above 40 degrees at night:  April 27th
  • air temperature reliably above 45 degrees at night:  May 22nd
  • air temperature reliably above 50 degrees at night:  June 23rd
  • air temperature reliably above 55 degrees at night:  July 15th (for 3 weeks)
  • air temperature reliably above 60 degrees at night:  Never

This year has been strange weather wise.  These are my 2010 stats thus far:

  • last killing frost in spring:  January 7th (Where I am at, it was a quite warm winter, but this could vary drastically depending on your location.)
  • air temperature reliably above 40 degrees at night:  April 10th
  • air temperature reliably above 45 degrees at night:  May 9th
  • air temperature reliably above 50 degrees at night:  May 30th (I may be going out on a limb here and may be proved wrong, but time will tell)
  • This is reported as being the warmest winter on record since 1940 here.
  • We had a record number of rainy days in the month of April (and I would venture a guess for May as well, but it hasn’t been reported yet)

So, what does all this mean for the vegetable gardener?  It has to do with the minimum air temperatures needed for vegetable growth.  This information comes from the WSU Master Gardeners of Clark County:  the base nighttime temperature needed for cool season vegetables (lettuce, spinach, beets, peas, potatoes, etc.) to grow is 40 degrees.  The base nighttime temperature needed for warm season vegetables(tomatoes, corn, beans, etc.) to grow is 50 degrees.  The base nighttime temperature needed for more delicate warm season vegetables (peppers, eggplant, melons,  etc.) to grow is 60 degrees.  Mind you, these are nighttime air temperatures needed for plant growth, not seed germination, which is a different thing, but very generally speaking, the optimum temperature for seed germination is 70 degrees.

Looking back on this year’s temperature stats, now that it appears to be 50 degrees at night, we can now plant out snap bean and runner bean seeds (it’s a little cool for them, so you could wait til mid-month if you like), tomatoes starts, cuke chitted seeds, and corn seeds.  Also bear in mind that this is the minimal temperature required for vegetable growth–they will all do better if it is warmer than this.  It will never get truly hot enough where I am to grow eggplant and peppers well, and so I grow them planted in the ground but covered with clear plastic at night, and then open it during the day.  This works well.

Hopefully the sun will come out one of these days and cooperate with us gardeners!

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