Aaron has a terrific post up about water issues and water harvesting at his blog, and he devotes an entire paragraph to the other end of the water issue - flooding, and drainage. Me, I thought that I can’t be the only person in the world who thinks it is worth more attention than that ;-). While I know that water shortages are the big issue worldwide, where I live, too much water is far more often the problem.
My area gets more than 50 inches of precipitation a year, a mix of snow and rain - and usually pretty evenly spread out. Our summers have warm days, cool nights and plenty of rain - now the summer 3 years ago when I barely had to water even my *container* plants because it rained so much is pretty unusual, but except for establishing seedlings occasionally, I have *NEVER* watered most of my garden. The hose doesn’t even reach it. The first two years we lived here were drought years, and even then, we did not water and things grew fine.
Part of this is because I live between two steep hills - most of the water runs down those hills, and eventually runs to the creek that borders the north side of my property. Before it gets to the creek, it runs across most of the rest of my property. During spring melt-off, we have several days of mild-to-moderate flooding. And once in a while, we get serious flooding, usually in early spring.
But even ignoring the flooding (and Aaron’s prescription to put your garden where it doesn’t flood is good), our soil tends to hold water. Waiting for things to dry out is the real limiting factor in gardening - it isn’t warmth we need (although that helps the drying) but enough dry out to be able to go forward. It really isn’t worth planting seeds into the muck - they simply rot. Transplants can sometimes tolerate it, but honestly, everything sits in the muddy wet soil (with the exception of a few plants that like it) and waits for dryer days - I’ve learned the hard way not to rush it, that plants transplanted a week later when conditions are better grow faster than the ones that sulk because their early conditions weren’t better.
One thing that I’ve discovered is indispensible to wet gardening is mulch - now much is made of the capacity of mulch to retain water. This is not exactly my issue. Instead, I use sheet mulch to protect my soil from flooding and heavy rains - the mulched areas shrug off some of the water, and the organic material helps absorb some more of it, so my mulched garden areas tend to look better after spring thaw, and to be ready to plant earlier. I rake away the mulch on warm day to let the soil warm a bit more, but I can be out on the mulched patches planting days ahead of any unmulched areas. I’ve never read any other garden writer’s discussions of the value of mulch in wet climates.
Generally speaking, as long as you have decent drainage and plenty of organic material, most garden crops tolerate the wetness pretty well - in fact, many of them like it. We do have problems with tomato cracking, and with getting hot peppers hot enough for me, but container growing helps with the peppers, and harvesting regularly before the rains with the tomatoes.
If you don’t have decent drainage, you may have to get some. At its simplest, you can dig a swale or trench and redirect water by hand. If you get fancy, and go for tile and backhoes, you are looking at money. We have areas still awaiting sufficient funds to justify the drainage work that is needed. Still, we do save on irrigation hoses ;-). And we try, as much as we can, to work with what we’ve got, to see our wetness as an advantage, that brings other species and possibilities.
Perennial plantings that aren’t wetland tolerant get the dryest spots, and they generally do fine. It is worth watching nature to see what does well - I have a thicket of cultivated plum trees in the back field that gets very wet in springtime - I was reluctant to plant much of anything but alders and elderberries there, because of the wet land, but native plum trees kept springing up, and I decided to take that as meaning I could get away with the cultivated type - and so I can, apparently.
Actual wet spots have their uses as well - I’m in the process of transforming the end of the side yard, which was uninspiredly planted to reed grass, into a wetland garden - swamp white oaks have edible acorns, beautiful wood and are great fungal hosts, buttonbush is a nectary plant that blooms at a helpful time for wild pollinators, primroses and irises add beauty, alders fix nitrogen and are a coppicing and mushroom hosting species, elders, blueberries and cranberrybush viburnums provide food for me and for wildlife - what’s not to love about wet spots! Not to mention the fact that the world is desperate for diversified wetlands - so not draining your land to get every single inch of cultivable space has some real merits.
The biggest problem, besides occasional flooding, of wet spots is leaching - the nutrients you place get washed away quickly, so fast you can’t keep up. This is another good argument for mulched soil in my climate, for lots of organic matter and humus in your soil, for terra preta practices, and for emphasizing slow release fertility rather than quick.
In the end, I personally like my wet spot - I’m grateful for the rains, and the snow. But living on the damp edges of the world requires, as all spots to, becoming native to that place and its conditions.