It is hard as heck to imagine that one of these days, I'll be longing for a hot day again, and for the fresh food that accompanies it, but it always happens. It is also hard, deep in the dog days, to realize that right now is when you have to start thinking about your fall garden. That's probably why so many of us start out beautifully, but peter out when the cold comes, running out of fresh things months before we have to.
Indeed, after a decade of working my farm, including the years when we ran a CSA, and many other years when we were gardening for ourselves, or raising perennial food and native plant crops for our nursery, timing the fall garden has been one of the biggest and most fascinating challenges - because there's so little information. There's much more now than there used to be, and creative gardeners, building on the work of people like Eliot Coleman have been pushing the envelope, but the emergence of expertise on this is a slow process of exploration that I've been engaged with for a long time. It involves changing both how we think about our gardens and also how we eat from them.
Historically, gardens in my region are usually planted on Memorial Day weekend, or around them. Potatoes and peas go in earlier, of course, and planting continues through June, but by the end of June, most gardeners are done. So come winter, they have a few cabbages, some kale plants or collards perhaps, and the ubiquitous brussel sprouts, but most of what has historically grown in this region is harvested by autumn, leaving months of eating out of a root cellar and pantry.
Now don't get me wrong - I enjoy eating out of a root cellar and keep a good pantry, but what I want is fresh stuff. It is one thing to accept that frozen kale and sprouted turnip greens are all you are getting that's green in February and March - although even that isn't wholly necessary - but it is another to pull the garden at the first frost and eat that way for six full months.
And yet there's a perception that you must have a greenhouse to eat out of the garden year 'round or close to it in a cold climate. This is not true - and I know this because I've been doing it for years, and I don't own a greenhouse. It is doable - even with the most primitive forms of season extension (some plastic, a few hay bales, an old window, some pots and windowsill) you can keep a reasonable progression of fresh stuff coming.
The biggest challenge in fall gardening is timing and crop selection. You need to choose the right varieties - things that do well in the cold. Then you need to plant them at the appropriate time. The difficulty, of course, is the combination of the two. You see, most of the things that love the cold, and can handle the cooler, darker and wetter days of autumn are not thing that love the hot, dry periods of high summer that they have to be planted in. It would be easier to wait until it was cooler and wetter, of course, but most crops need to complete their growth in northern places by sometime in September, so that declining light doesn't slow them to a halt.
There are some tricks I've found useful - the first, of course, is start seeds inside. Many seeds of cool weather plants don't germinate well in hot weather - but your house is generally cooler than the outside is. Planting in the shade of deciduous trees is also helpful in some cases - most greens (and greens are among the best crops for cold weather) will do well with less than the 6 hours of direct sunlight per day that are usually recommended for vegetables crops - in high summer, four may be enough. If you have trees that lose their leaves early (I like birch for this), planting beneath them is a good way to give some shade and protection early, while giving them full sun late.
Timing your planting for a spate of cool wet weather is good too - if you know you'll have a few days of rainy, overcast weather, that's the time to get out there in July and August - many plants can tolerate the heat if they've gotten a good start.
Plant seeds deep, so that they come contact with residual soil moisture deeper in the earth - shallowly planted seeds may dry out and never make it. To conserve irrigation water, consider nursery beds for plants to be transplanted later - perhaps right outside the kitchen door for sink water or other sources of ample water.
Container gardening in fall is wonderful - plants can be started indoors or brought into shelter during the worst hot, dry spells, and then brought back under cover when things get cold, keeping you in veggies for a long spell.
Besides the basic tips, you'll probably have to do some experimenting. Before you do, though, talk to other farmers and your local extension agent about crop timings. Remember that in times of declining daylight, you'll need to add 10 days to 2 weeks to the usual packet info for days to maturity, and most of the growth must be done before the biggest declines. In my climate, it means that growth largely stops by mid-September, so July and August are the primary months for winter planting. In other locales, later can be better - especially hot dry places that rely on fall rains.
Fast maturing and cold hardy are what you want, but don't underestimate the value of heat-tolerance along with cold hardiness. Collard greens are a classic example of a heat and cold tolerant crop, but some winter lettuces, arugulas and root crops handle both the hotter dryer days of summer. Variety selection is essential - seed catalogs are good for this (Fedco seeds carries varieties of seed specifically for fall planting, and Territorial Seeds publishes a fall planting catalog, geared towards the Pacific NW), and so is the wisdom of local gardeners and farmers.
If you would like to put some more depth into this, I still have more spaces in my fall and winter gardening online classes, where we'll cover specific varieties, season extension techniques, container gardening, mulching, root cellaring, overwintering, stratification, containers and cooking from the winter garden and more. Email me at firstname.lastname@example.org for more information (the syllabus, btw, is a few posts down!)