Moving Vegetable Plants to a Warmer Zone without Changing Zip Codes

Now that we’re into a new year and the Christmas decorations have been packed away, it’s time to start making some preparations for the garden.  In previous years I could consider planting peas in very late February without any special protection if the conditions were right, but I’m one zone colder now.  On top of that, we are on the side of a mountain that faces north.  The sun doesn’t actually hit the ground here until about an hour after it hits my next closest neighbor’s yard.  So even if I could warm the soil up, without the sunlight to grow the seeds, planting any earlier would be a waste of time for me. 

That makes heating up the ground all the more important so that my veggies can get as quick a start as possible.  Believe it or not, it’s actually possible to plant as if you live in an area that is up to three zones warmer, especially if you employ a couple of options together. 

1.  Walls (whether belonging to the house or other structure or retaining walls) can store, release, and reflect heat.  Take advantage of the free heat supplied by walls by putting plants in right next to them. 

2.  Dark compost placed around the plants helps to warm the soil and hold heat during the night.  Compost or still decomposing garden and livestock waste also release a small amount of heat as it is decomposing and slightly raise the temperature.  In addition, compost helps hold water, and water helps hold heat.  Dry soils are much cooler.  However, don’t overdo the water—soggy water can drown seedlings.

3.  In raised beds, raised boxed beds, or even just raised furrows, the soil warms up much faster and with this practice alone you’ve moved your plants one full zone warmer.  Every year in Reno, I turned the soil in the raised boxed beds.  The compost or still decomposing material went into the bottom half of the 20” high beds and then was covered with the soil that had been on the bottom of the bed the previous year.  The soil warmed quickly and I was able to plant tomatoes (also protected with other means) in mid-April.  My neighbors weren’t planting their tender vegetables for another 5-6 weeks. 

4.  Row covers can be used before and after planting.  Options like plastic sheeting, including simple drop cloths, can be quite effective.  (The jury is still out on whether black or clear plastic is more effective.)  Old sheets and tablecloths, and even transparent garbage sacks will do the job.  Commercially produced garden fleece/row covers can raise the temperatures 2-8°F.  Frost blankets, normally used at the end of the season, can protect plants down to 20°F. 

Before planting:  You need the temperature to reach 44°F consistently for planting.  Plastic is probably the best and least expensive choice here and is particularly effective when you've got heavy clay soils.  Whichever type of row cover you choose, put it in place 2-6 weeks before planting to warm the soil up fully. 

After planting:  Place old sheets or commercially produced floating row covers over vegetables to keep them warmer and prevent pests from gaining a foothold.  Plastic can also work, but it mustn't come into contact with the plants.

5.  Cloches are simple covers individual plants to protect them from frost, to warm the plants during the day, and to help retain water.  The disadvantage with them is that if not carefully monitored temperatures can rise too much, killing the plants they were meant to protect. Cloches run the gamut from free to rather expensive.  Some of the best options are milk jugs, soda bottles, and water bottles.  You simply cut the bottom off and push them into the loosened soil around the seeds and seedlings.  Another bonus of using these DIY options is that you can easily remove the cap for venting on warm or sunny days.

6.  Wall o’ waters are a particular kind of cloche.   The 14-16 vertical channels are filled with water and then pressed together to form a protective teepee around the plant.  Like other cloches, they retain moisture and heat.  Unlike the others, they can protect from freezing temperatures down to about 20°F. 

7.  Cold frames are open-bottom boxes most often with wood sides and a hinged glass top that can be opened for harvesting the vegetables growing therein or simply venting to keep tender plants from burning on sunny days. These unheated structures harness the power of the sun to get a jump start on the gardening season and protect tender seedlings from harsh weather conditions common to early spring.

Any one of these practices will make the particular patch of garden where it is used ½ to 1 zone warmer.  Combining two or more can give you up to three zones.  Keep in mind, however, that it’s also possible to have too much of a good thing.  Each layer of protection may prevent up to 10% of the sun’s energy from penetrating.  If you put a milk jug cloche over a tomato plant, then add a wall o’ water, and finally cover with a row cover, that’s 30% of the solar rays that aren’t getting through, and it can detrimentally affect plant growth.

All this talk of gardening is getting to me.  It’s only been 3 months since the season ended, and I’m already itching to get back out there.  I’ve got 6” of snow on the ground and another 4-8” in the forecast for the next 24 hours.  I guess I’d better start looking at what I’ll be starting inside this year.