That rather depends on your zone 9b. That label only tells us about your average minimum temperatures. It says nothing about your winter weather in terms of heat, wind, light or precipitation. I also live in a 9b but I couldn’t sow or plant any of those crops this late except the garlic.

maybe not a hoop house, but row covers would be cost effective and have other benefits like insect exclusion...

Your overnight temps in the mid-30's is a problem. You can put in your garlic, and might possibly get some minimum temp germination with the spinach... but still too chilly in the minimum temps for the rest of the seeds to want to sprout and grow. Many seedlings don't really like temp changes between 30's nights and 70 degree day either.

I don't know if you need a hoop house. But if your temps are in the fridge/freezer area, the seeds likely will need some protection.

Thanks for the replies here, folks.

Chadinlg, row covers, eh? Is this something I would put on before sunset and remove the next morning?

Beesneeds, can you be more specific about what kind of protection I might provide? Would the row covers be sufficient?

I'm sorry to say I have no idea what kind of protection you might need in your area. I live in the frigid north where if there's seeds outside this time of year they are wintersown, not active grown. In the spring I don't tend to try planting much seed out till the overnight temps are more stable into the 50's. I try to get closer into optimal seed sprouting and seedling temps rather than minimums. Freezes and snaps happen, and even with protection I can lose seed babies out in the garden if I plant out too early.

You are also planting into winter, something I don't do. So I don't know how well your seeds will fare if the weather gets worse during the next few months.

All that said, if you were using a season extender for fall crops of those veggies... I would still recommend frost cloth at least to help stave off those below fridge temps. With seedlings, maybe super heavy frost cloth and also plastic hood as a row cover might work? A hoop house might still be better, for ease of moving around inside with the plants.

In my unheated solar greenhouse, the nights have been down in the 30s and sunny days up in the 70s or 80s for a good month now. I planted kale seeds last week and they germinated yesterday or the day before (mid-Dec). I know from previous years they will grow very slowly in the middle of winter, but they don't mind freezing nights, and they'll boom forth in about February when things warm up a little. The lettuce, spinach and arugula I planted back n September are growing great at the moment.

Thank you all for chiming in. I decided to go ahead and purchase the materials for the hoop house. If nothing else, I might get an early start with my dahlias next spring. And maybe it's just an excuse to spend more time in the garden instead of inside on my computer.

I picked up a string of old fashioned incandescent Christmas lights, the big (C9) kind, which I'll string inside the hoops in the hopes of adding a few degrees of nighttime warmth under the material. And I've opted for row cover instead of plastic, as I read that in my relatively mild winters, the row cover will do just fine and allow water and light to come through.

I haven't erected the hoops yet, but the lettuce, broccoli, and spinach plants seem to enjoy the cold weather and are doing well. It's a crap shoot whether the carrot and beet seeds will germinate at this point, but I have confidence the garlic cloves I planted today will do just fine. Just feels good, even on the coldest of days, to have your hands in the dirt.