For our latitude, we have a rather long growing season here in the Treasure Valley, from about May 9 to October 9. That is the average date of last frost and average date of first frost respectively.  Even so, you can extend that growing season further for many crops with the aid of row covers or plastic.

Plastic is less effective, because it does conduct cold. If foliage touches cold plastic, the cold will be transmitted to the foliage.  Row cover material is a pressed polypropylene fabric that comes in very lightweight bolts, covering enough to bar insects from laying their eggs on your plants, and heavier bolts, some heavy enough to protect from four or five degrees below frost.  They admit light and water, so may be left on for a while.  They do not conduct cold. 

If you build raised beds like mine, you’ll find it a great advantage to set clamps about every three feet along the long sides of your beds so you can slide arches of 3/4 inch diameter pvc into the clamps.  These clamps are commonly available in building supply centers, sold for clamping electric conduit to walls.  Be sure you buy the size that will take the 3/4 inch pipe.  Half inch pipe isn’t strong enough to arch high over your bed. 

You can buy “garden clips” that look vaguely like women’s hair curlers through Nichols Garden Nursery ( www.nicholsgardennursery.com ) or almost any other garden supply magazine.  They clamp the row cover fabric securely to the arching pvc pipes without tearing the fabric. This treatment makes your raised beds look like Conestoga wagons, but whatever you’re growing is quite safe and snug.

 You can get a really early start on lettuce and spinach, for instance.  Growing any green leafy vegetable under row cover is the best way to go, because the cover keeps the greens shaded enough from the sun and wind to keep them tender and succulent, and insects are at a minimum.  If you try to grow lettuce or spinach in the Boise area without row cover, you’ll think you never had seed germination because California quail will eat your crop to the soil.  The row covers effectively bar quail.

Crops I do not like to plant out early are tomatoes, peppers and eggplants.  Eggplants are magnets for flea beetles that eat so many tiny holes in eggplant seedling leaves they may kill the plant.  When eggplants grow more mature, flea beetles lose interest in them.  (Flea beetles prefer Asian leafy mustard greens even more than eggplant, so you can attract them away from the eggplants when you finally do transplant them.)  Someone did a study a few years ago that indicated that tomato and pepper plants subjected to nighttime temperatures below 45 degrees were thrown off their diurnal rhythms so far they didn’t even recover by harvest time.  Those plants yielded much less than plants set out later. 

I usually set out tomatoes and peppers about June 1.  Even before the study indicating a reduced yield following a cold night, I found that I didn’t really gain anything by setting those crops out before the first of June. 

I like to plant potatoes or peas, at least, on St. Patrick’s Day. 

Thanks to Ross Hadfield’s experiences, I’m going to plant lettuce on Thanksgiving.  I know many in this Valley plant spinach in fall too, then enjoy very early nutritious greens. 

Incidentally, season extending goes both ways.  The row covers over those PVC arches also protect frost-tender plants in those beds from early fall frosts.  Plants such as squash, melons, sweet potatoes,  beans, and cucumbers get extra growing time in autumn from row covers.  They’re not really sufficiently tall to cover tomato plants.  If you, like me, grow tomatoes in cages, though, you can use clothespins to fasten old blankets, mattress covers, etc., over the tops of your tomatoes and prolong that harvest.