Plants that can handle freeze-thaw

[Jeremiah Robinson]

This past winter, I grew some spinach and lettuce in my greenhouse AP system, and some spinach in the regular garden.

Most of my AP spinach died, while the garden spinach mostly lived (under a low tunnel).  

I suspect that the AP spinach died partly because of the almost-daily freeze-thaw it had to undergo. The roots stayed at 50 but the leaves alternated between 50 and zero.

Interestingly, the AP spinach that did survive went total nuts come spring and grew 2.5' tall.

So I have two questions:

1. Do you think that it's the freeze-thaw that probably killed my spinach?

2. Are there certain plants that can handle not just cold but constant freeze-thaw?

[kimlee kingston]

It is possible the freeze-thaw killed some of the spinach. Other factors may be at work. Sometimes a plant will survive and thrive, while a plant of the same variety, raised under identical conditions, will keel over and die.It could be the water temperature in your media beds.

You might try a heat lamp above a mini tunnel inside your AP greenhouse. This will add another zone to your growing season inside your greenhouse. I live in North Texas, zone 8, and this is how we grow salad greens and snap peas during our unpredictable cold nights. 

[Jeremiah Robinson]

Thanks KL.  I like the idea of a lamp over the beds but inside the low tunnel.  If I do bubble wrap low tunnels like Jim I might get away with a lower wattage lamp.

I know that spinach starts to bolt when days get too long.  Do you have problems with bolting when you run lights at night?

[kimlee kingston]

You can absolutely use a lower watt bulb.  We only use the lights on cold nights, 40F or less. We get plenty of sunlight during the day, even in winter, so the lights are only necessary on the cold or overcast days. 

The AP greenhouse really makes a big difference in our seed choices. We have a hoop design, covered in window screen mesh, 63% shade cloth over the top, south facing door, north end partially shaded by a large oak tree. There is no middle ground ... it is either hot, very hot, or very cold. Sometimes all in the same day. Sometimes it is a surprise.  This is not the situation since we built  the greenhouse. I believe we have at least achieved zone 9.

We have a long growing season here. I put aside a couple of nice healthy plants just for seed in the wicking bed every few weeks,mainly broccoli, lettuce, spinach. Leafy salad plants will normally bolt here when the temperatures are in the +90s. The air is too hot.

We're having a mild spring, and this is rather pleasant. Our summer begins in May, often it is still in the 80s-90s deep in the Fall, even on Thanksgiving Day.

Jeremiah Robinson said:

Thanks KL.  I like the idea of a lamp over the beds but inside the low tunnel.  If I do bubble wrap low tunnels like Jim I might get away with a lower wattage lamp.

I know that spinach starts to bolt when days get too long.  Do you have problems with bolting when you run lights at night?