Yep, too warm. And hopefully you aren't heating the soil too?

Dave

Spinach bolts from a combination of lengthening days and increasing heat.

If you have problems with growing SPINACH, try CHARD. I especially like colorful Swiss Chard. IMO, they have better texture (less water), easy to grow, and will hardly bolt, if planted in the spring, in partial sun.
You can use them exact the same way as spinach (as young) or let them get bigger.

I read somewhere just a few days ago that bolting is triggered by it being warm at night (in the dark?). If you can't cool them off, maybe you could try leaving your lights on. IMV 70 degrees doesn't seem that warm. I'd also agree with digdirt. Don't have them on a heat mat. I've had trouble germinating spinach on a heat mat.

Hi folks

Thanks for the input. I didn't use a heating mat but I did leave my fluorescent tubes on 24/7. Maybe they are generating a bit of heat?

Thanks

Scott

Spinach bolts when the light hours per day exceed 14.

Hi DrScott, it's nice to see someone else near me. :)

When I was little, my parents taught me that plants are like people. They need to sleep. If they don't, then strange things start to happen like what you are observing. Spinach is a cool weather plant, so it will do best without a lot of heat in either the soil or the surrounding air. It sounds like the odds are good that your lights are creating two much warmth and making the day too long. I would try turning them off at night and keeping an eye on the soil temperatures.

jean001, thanks for posting about day length sensitivity. I read it someplace but don't remember where (pre-internet days I think) but since I started planting spinach as soon as possible in the spring here in NH, I've gotten a good crop. I direct seed. I think the easiest way to get early spinach would be to direct seed in the fall and let it overwinter. That worked perfect for me one year even when we had little snow cover. This is our second winter with a high tunnel and last year we had too much spinach in winter so I didn't direct seed in the outside garden.

I direct seeded some about two weeks ago and they are emerging. The weather here at the PNW, has been in the range of low 30s to low/mid 50s., with lots of rain, clouds. This tells me that you should germinate Spinach in cool temperatures. You don't need a heating mat, You don't need too much warmth. Probably an unheated garage would've been just fine.