1. start plants indoors about 2 months before last frost date, then harden them off before setting them out. Gives them a head start to make up for the shorter growing season

2. for warm-season vegetables such as peppers and tomatoes, buy seeds of earlier varieties (I order them from a couple of suppliers in Manitoba)

3. grow root crops such as potatoes, onions, turnips, rutabagas, carrots, beets which do well in short season areas

4. it's a good idea wherever you live to enrich poor soil with composted manure, peat moss, compost etc. - to give your plants optimum growing conditions

5. where possible create a micro-climate such as barriers (fences, hedges etc) to keep out cold North winds

I live in Northern Ontario Canada. Thanks to the new earlier cultivars I can grow almost everything I like in my garden, even sweet corn. Of course there are some limitations to living in a Zone 2b-3 area but these challenges make the successes all the more rewarding. I can honestly say I've stopped having zone envy. Today Northern gardeners are only limited by their resourcefulness.

I do many of the same things canadian daisy does and I too buy varieties that have an early maturity date.

I have a greenhouse which I open the second week of April, and start my seeds then. When we built the greenhouse we took into consideration heating it. It just clears my head and has a onesided sloped roof. We made it very air tight and with double walled polysterine so it retains heat and with vents that I can open if it gets too hot. I have a heater in my greenhouse but most days the sun is enough to heat it and it is set to just above freezing at night.

We use row covers on some things. This raises the temperature by 2 degrees under it, yet still gets 85% of the light. It warms the soil, yet rain and watering goes through it, so there's no need to take it off until the weather is warmer. On some things like carrots we leave it on all summer to keep out the carrot rust fly.

We soak hard seeds like beans for a day or 2 before we plant them. We always pour water in the trenches before we plant anything. This gets the seed or plant off to a good start germinating or growing because the moisture is right there and doesn't have to seep down through the soil.

You could try wintersowing so you could get hardy plants started earlier.

You could bury borderline hardy plants deeper to ensure it's survival during harsh winters.