When I lived near Philadelphia we started our seeds indoors. We only did it with tomatoes. At least with them you can plant them deeper, because they get so leggy. You could probably find all the info you need at your local ag. center. I've learned alot from mine.

I agree that your local county extension office could be a wealth of info.

But you don't mention a couple of crucial aspects of season extension and to understand it you have to focus on them. First is has limited effectiveness the further north you are and second, soil temps.

So in your zone you may gain a bit of time but you may be fighting a losing battle if it is multiple weeks you are hoping for.

Air temps is only one aspect of season extension and only applies to established plants and is primarily a fall concern.

If spring extension is your focus then it is soil temps and methods of raising and maintaining them earlier you need to focus on. Things like close monitoring of soil temps, raised or mounded beds, heavy use of black plastic to rush ground thaw and to warm the soil, soil tilth to improve drainage and encourage early warming, etc. Only then do you worry about covers/enclosures for the plants once they germinate. Cool season crops are quite tolerant of cold air temps but they will not germinate or survive cold soil temps.

Dave

What Dave said. Soil temps. are key. Also, with cool season crops, there is no definite time or temperature they kick the bucket (unlike the convenient 32 F for warm season crops). You'll just see quality declining as the weather gets colder and colder in the fall and you'll get a feel for up to when it's worth the effort. Same goes for the spring. If you push the envelope too much, you'll find out in terms of slow growth, a large number of plants being damaged, etc.

So how many weeks earlier you can transplant cool season crops in the spring depends on YOUR goals - is it for fun? Or do you have a family to feed that depends on this? As a very rough rule of thumb for cool season crops, I'd say 2 -3 weeks earlier in spring, 3-4 weeks later in fall is a safe bet for what you'd get with a low tunnel combined with row covers. For warm season crops, the window is much shorter.

Your cool-season starts should be hardened off really well by exposure to near-freezing temperatures for a few nights before you transplant.

I'm just a novice but happy with my small successes this year. I warmed up soil with plastic. My husband made a short low tunnel covered with Agribon 19 (or 15) for my experiment this year. Here in NH it only takes one night of low temps to destroy a planting and typically we seem to have just one night and then a run of warmer nights. I lost a promising bean planting one year. Lots of blossoms and then one cold night the third weekend in september.

I have to be away during prime planting season so this year I experimented with the tunnel. It was just big enough to cover three close rows. Bush beans, a filet variety, were planted in early May. We then got a period of cold and rain. I heard beans just didn't germinate. Mine did!

A late planting of beans this year was also protected by the tunnel. We were picking beans up until it snowed on Oct 30. We did not care for the taste of a wax bean but I think it's the variety not the cold. The green bean, again a filet type, were superb. The tunnel suffered damage during the snow so I'm not sure if any bean plants survived.

Pay attention to varieties. I also picked unprotected lettuce on Oct 29. It will be interesting to see if any survived the 12" of snow.

Next year we plan a high tunnel covered with plastic. My goal is fresh bush beans until Thanksgiving. A friend of a friend who uses plastic low tunnels and starts plants indoors is eating zucchini in early June when my plants are just getting established. I think he easily gains a month here in NH. Many people around here consider

Memorial Day weekend to be the safe planting date for warm weather plants. I don't agree. I have a sweet spot on the south side of our house, a narrow bed against a white house. We picked peppers when frost was predicted but left some small ones on the plants. The plants didn't get touched by frost until Oct 29.

I use a calendar on Johnny's Seeds website as a guide.

Also, we visited a neighbor with an unheated greenhouse who has greens all winter. Make sure you pay attention to the last planting date because plants stop growing during the short days. From what I gathered at my first NOFA conference this year, if you didn't get things planted by mid-Sept, they didn't germinate and grow enough before they stopped growing for the year until the days get long enough again.

Best wishes.

Here is a link that might be useful: Johnny's Seeds guide

My experience is that you can safely plant about 3 to 4 weeks early under a low tunnel. If its too cold the seeds just will not do much until it warms sufficiently. But once they germinate they really take off! (no wind, consistent humidity and generally warmer). If you are looking for that first heavenly home grown tomato, pepper or other hot weather crop it definitely is the way to go. Remember the sun can really warm up those mini green houses so you will pay attention. Ive seen charts that provide under plastic sowing dates by region, just look around. Also just because you are under plastic don't for a minute think your crop is immune to pests...slugs and others will show up so you will have pay attention. I also use my low tunnel and cold frames to start seeds in little starter trays to great effect.

I highly recommend using a little plastic to get a jump start on the season..Spring is coming!

Thanks guys. That wad exactly the help I was looking for. So my idea is to set up the tunnels in Feb and see how that warms up the soil by march and then start seeding cool season in early to mid march. Hopefully that way I can harvest early enough to get warm season crops out on time in may.