when you buy in mixes you may never realy know what is in that mix, so along those lines we don't do it. also regular feeding of plants could boost the nitrogen so much so that it can affect the productivety of the plants in a negative way ie.,. grow more foliage, there again we have never applied liquid fertilisers nor do we add any man made concoctions on a regular basis, add hock we use some organic lifter which is a product made from chook poo.

we feed our gardens our vegetable and kitchen scraps (anything that rots), and mulch using green type spoilt hay or sugar cane mulches along with my wee water mixed with dish rinse water mainly, ths is all the nutrients that our gardens derive, and our plants are strong, healthy and produce very well simply.

check the pic's on our site on how we do our gardens.

len

Here is a link that might be useful: len's garden page

I also gardened in Zone 4 (Northern NY) before I moved to Maine. To get a decent yield of warm-weather crops like tomatoes and eggplants, I had to use season-extending mini-greenhouses.

There were simple structures of light wood frames and large sheets of bubble wrap, about 6' X 20' used for wrapping canoes for shipping. (Photo in the link below from my old website.)

Keeping an eye on the Weather Service forecasts, I'd close them up at night when frost was indicated and open them early the next morning to prevent the plants from frying when the day warmed up. After the early September frosts, there were sometimes weeks more of good growing weather before I had to tuck them in for the night again. I could keep tomatoes, peppers and eggplants going into mid-October this way.

I also kept lots of sheets of plastic and old sheets handy to quickly cover other unprotected plants during frost warnings.

Hope this helps you get them to harvest stage. We'll have all winter to think about how we can do better next season.

Here is a link that might be useful: Season Extenders