Cheating

The absolute bestest thing you can invest in to make gardening easier is a greenhouse. A nice one will only cost you about $10,000 after all.

Yeah.

So, what else? Well, we have on two occasions bought white car covers to use as greenhouses. They work VERY well, cost a fraction of an actual building (we paid no more than $300) and we have recommended them to many people. Unfortunately we have lost both of them to the extremely windy conditions up here. The first one actually took off, and ended up in the field across the road. The second one, firmly anchored this time,  just disintegrated gradually from the constant strain on the seams. We may or may not try again, but there are other ways.

We did once also build a small lean-to greenhouse from wood. It cooked everything. Temperatures inside got so hot in late afternoons you couldn't even enter it. We made the foolish mistake of using plain glass, like the greenhouses we'd known as children in England. NO. In an Ontario August you need diffused light. We could have painted the glass white, but it was too small anyway, so we took it down, and tried the car covers instead.

I am still planning a large, wooden, solid greenhouse, and will get there eventually, but my experiences so far have taught me that really all you need is:

a) A structure, any size.
b) A cover that lets light in, but not too much.

You could use a milk crate and some grocery bags taped together. It would be ugly, but it would work.

If you have lots of money to waste you can buy all manner of mini structures with covers that will do the same job. They will be far prettier than the milk crate/grocery bag combo, and your neighbours will be less likely to say rude things about you, but they won't actually be superior. Our Mennonite neighbours use old feed sacks over wire frames to make rows of cloches, and it doesn't look bad at all. They pull the sacks back as the season/day progresses, to prevent overheating. I might try that.

Another way to get a head start on the season is to start plants in pots/trays, put them out during the day and take them in at night. I did that one year and drove myself crazy because I had over a hundred trays. It's far more doable if you only have a few. Again, the Mennonites have a method here. The trays are all laid out on a small wagon, which is pulled into a shed at night.

As a last resort, you can protect plants that cannot be moved indoors by throwing an old sheet over them on a cold night. Unseasonably late frosts are the bane of northern gardeners, just when you think it's safe...wham. I err on the side of caution to avoid tragedies like that and wait AT LEAST until the last week of May to plant out tender things. Don't assume that just because the tomato plants are available for sake, that it's planting time. Check your own local "last frost" date.

Fortunately not everything is delicate. Peas can go in the ground as soon as it thaws out. If they get too cold and wet they will rot, so make sure it's not soggy soil, but I dare to put them in earlier and earlier, and last year we started them in March, and had our best crop ever.

Despite what they tell you, anything can be started in a pot. Even carrots. So if you have ANY way of cheating, by starting plants inside, grab that opportunity. Just make sure that when you plant out you don't disturb the roots. One way to do this is to make the pots from paper, and plant the entire thing. The paper soon breaks down in the soil. Make a few holes in the bottom so the roots can escape while that process occurs.

http://www.homemadesimple.com/en-CA/HolidayandParty/Documents/newspaper_pot.pdf

We have even started corn inside using this method, and will do so again, results were so good. Remember every week extra you get at the beginning of the season, is a week sooner you'll be eating your veggies or enjoying your flowers, and it could make all the difference if frosts come early in fall.

NOTE: I've decided to add links to other ideas as I come across them, here's the first of these updates:

http://www.soyouthinkyourecrafty.com/2012/07/cd-case-greenhouse-tutorial/

Don't forget to check the comments below for other suggestions, there are already a few, and please remember you are free to add anything yourself!