Planting schedule for edibles in an unheated portable greenhouse

Unheated, portable greenhouse
Sunday, December 10, 2023

My new edible gardening tool is a walk-in greenhouse.  I have had portable greenhouses since 2008.  I have grown salad fixings in them over the winter to keep having fresh salads and they have worked incredibly well at this.  With a walk-in greenhouse, I am looking to expand the growing season for other edibles.  This is what I have researched so far.

 

The impetus for getting a walk-in greenhouse was to be able to keep my tropicals outside for as long as possible, to overwinter the natives I dug, separated and put in quart pots, and to extend the season in the fall and spring for the summer lovers like tomatoes, peppers and eggplant.

 

For the tropicals, I was able to keep them outdoors for an additional month, bringing them inside yesterday.  I believe they would have been fine for another couple of weeks, but they were forecasting a low of 24 tomorrow night.  They already survived down to 22, but that was earlier in the fall when the ground was warmer.  I have left the potted peppers and eggplants in the walk-in greenhouse.  If they survive the hard freeze, then I’ll know the tropicals would have survived.

 

The potted peppers and eggplant did get damaged from the 22F freeze, but I had not velro’ed the windows of the greenhouse shut.  I had rolled the windows down, but should have used the Velcro closure to seal out more of the freezing air.  It will be interesting to see how long the summer lovers will survive in the walk-in greenhouse this winter.

 

For me, gardening requires research and experimentation.  I read up on what I want to learn more about and then go try it in the garden to see what works or what adjustments I need to make for my garden conditions.

 

One thing I do know about summer lovers is to be sure that you are keeping their stems and leaves off of the plastic.  Any part touching the plastic will get killed when there is a hard freeze.  You can also add mass inside or outside of a greenhouse to help moderate the temperature inside the greenhouse.  Mass absorbs the heat during the day and then releases it back at night.  The best exchange is when the mass is inside the greenhouse.  If you don’t have room, putting it outside the greenhouse up against the walls will help.

 

I was going to put a layer of straw bales around the outside of the walk-in greenhouse, but didn’t get around to buying the bales.  For the portable greenhouse, I have room to put gallon jugs around 3 of the 4 sides.  I spray paint the jugs black to protect them from the sun’s harmful rays.  Sun will break down the plastic, causing the jugs to become brittle and crack.  If you leave them in place with holes in them, they still work but come summer, you have created a mosquito breeding farm!

 

For the walk-in greenhouse, I left the potted eggplants and peppers around the walls and replaced the tropicals with the quart pots of transplanted natives in the center.  I left enough room to be able to walk into the very center of the greenhouse so I can water as needed easily.  My smaller greenhouses only need to be watered a couple of times during the winter after being closed up.  This winter, I will learn if that is the case with the walk-in greenhouse.  For the smaller greenhouses, the moisture from the pots evaporates, rises to the plastic and then condensates back onto the plants; kind of like a terrarium.  Hopefully, the walk-in greenhouse will be at least as close in water efficiency.

 

As it warms up in the spring, I plan on adding shelves around the perimeter of the greenhouse to be sable to start seedlings sooner in the spring.  I have been looking back in Eliot Coleman books on gardening year round utilizing unheated greenhouses.  I have 2 of his books “The Winter Harvest Handbook” and “Four Season Harvest”.  Since he lives in Maine, I am going to adjust his spring dates by 6 weeks and his fall planting dates by 5 weeks since this is the difference between the frost dates in his area versus the frost dates in my garden.  It may not be that simple since I’m using a tiny greenhouse and he uses huge greenhouses, but it gives me a place to start.  My last frost in the spring is April 2 and my first frost is November 3.  You can adjust your planting dates by taking the difference between my dates and those in your garden.

 

For spring, here are my adjusted dates for starting the seedlings in the greenhouse:

Mid-February-beets, greens, carrots

Mid-March-zucchini, peppers and beans

Early April-tomatoes, cucumbers, squash, watermelon and eggplant

 

Fall is different in that you are starting your fall and winter crops at the end of summer with the goal of getting them to full size by the time daylight hours drop to 10 hours.  For me, this is November.  Growth slows during the fall as daylight reduces and temperatures drop.  My initial plan is to move the seedlings I start in late summer to the walk-in greenhouse when the temperatures dip.  By moving the seedlings into the walk-in greenhouse, it will hopefully help them grow quicker in the warmth.