Go for it! Spinach is quite forgiving to grow. It can take temps well below freezing, and with some water barrels, your insulated greenhouse, and some frost blankets over the plants at night, I bet you won't need the heater. You may want to germinate the seedlings indoors because it will go a lot faster if it's warm. I am pampering my current crop of seedlings, with a warm spot in the greenhouse by day, then I bring them in the house at night.

I don't think spinach is fussy about soil, So I think any kind of improved soil will be fine.

My best advice for stuff like this is to just give it a shot and see what happens and then learn about what you can improve next time. Since seeds are cheap, it allows for plenty of easy experimentation.

In addition to spinach you can try greens like mizuna, arugula, kale, etc. Whatever taste you prefer, they are all easy to grow.

Good luck!

You might be too late for this time of year. I'm still in the reading stage and hope to have a high tunnel in the spring but I thought seeding needs to be done in September for some growth before the short days. According to Eliot Coleman's books, plants stop growing during the shortest days.

Here's a link to Johnny's Seeds about short days/long nights
http://www.johnnyseeds.com/t-catalog_extras_vegetables.aspx#daylength

but also read the section on Over Wintering that mentions how spinach will go dormant (you can still harvest) this time of year. Day length depends on where you are located.

Here is my spinach in one of my unheated high tunnels.

{{gwi:117214}}

The far left was planted on September 17th, Next bed, September 24th and last bed was October 1st. As we move right, we had better germination. We started harvesting from it November 5th.

For more information, look at the link below.

Jay

Here is a link that might be useful: High tunnels and spinach planting dates

I forgot to add, this picture was taken around November 1st. The bed on the right has Radishes and Haikuri Turnips.

Jay

Raised beds are not a good idea for fall and winter growing. They are far more likely to freeze when compared to in-ground beds. That being said, you are in zone 6 and your winters may be mild enough either way. I would encourage the use of row covers as well to help insulate *both* the spinach plants and the beds you plan to put them in.

Jay... through how much of the winter do you grow these crops? I am asking because i am curious about my own results. I am in zone 5b and can grow spinnach through the entire winter with no heat and it survives nicely. It is the only crop which doesn't seem to stop at all. I get no frost damage. It does tend to go to flower in early spring. Didn't take notes but i am guessing early to mif April...

Thanks for any thoughts.

Poppa

I will harvest it all winter long, with out any problems. I need to start putting row cover over it, but I haven't had time to get that done. Once it starts to get below 20 degrees every night and the days don't warm up. It will be covered.

Jay