Coping with Climate Extremes: Wet

Living in drought-stricken California, I welcome additions and observations from gardeners further East, who have experienced heavy rains,  flooding, or massive storms. My own experience with gardening in wet soil comes from the Alaska rainforest, where summers are very cool and rainfall is constant but seldom torrential. Here are some tips that have proved themselves in my gardens and for gardeners in the South:

The necessities for any garden are water, nutrients, air, heat, and light. These lead to biological activity which leads to plant growth. In wet or flooded conditions, the excess water crowds out air in the soil. Wet soil is constantly being cooled as water evaporates off the surface. (This may not be a problem in the south. Further north it is a major obstacle.) So the big initial challenges are to replace anaerobic soil conditions with aerobic, active ones, and possibly to warm the soil cooled by evaporation.

1. If soil is utterly sodden, trying to work it or even step on it is problematic. If you need to get a garden going and don't have time for things to drain or dry, consider using containers to get started. Or dump a pile of potting mix, & compost on top of the soil and plant in that.
2. Air is critical but you don't want to damage the soil structure. Start by poking holes as you would to aerate a lawn. Pull aside any mulch or covering. If there are plants in place, leave some there, with air space around them, to draw moisture up and out. You don't want a dense canopy preventing evaporation, but even a dead plant here and there can act as a wick to evaporate more water out, if there is good air circulation all around.
3. When you can't dig yet, earthworms can. You don't want to cover the whole bed, but a stripe of compost or a few blobs of compost or woodland duff dotted down the bed can jump-start aeration.
4. When you start to plan and prepare a planting bed, go narrow. University of Alaska researchers found that 18-24" is the maximum width for good drainage and biological activity in wet, cool environments. Make rows that are 8-12" high and 18" or less wide for very cool areas or very wet soil.
5. As you are planning those rows and plantings, remember to space plants more widely than is recommended. You don't want them crowded together, because it reduces air circulation. Good circulation is your first defense against plant diseases, which flourish in damp conditions. For the same reason, avoid unnecessary fencing, enclosures, and plantings. Let air sweep through the garden. If wind is a problem, use a porous, partial barrier that slows wind but doesn't produce dead air. For both frost and disease protection, make sure there is somewhere for cold or soggy air to drain away if possible--ideally downhill from your garden, or at least downwind.
6. Plant disease-resistant varieties. If your climate is getting rainier, you may need to add new varieties to your lineup of favorites. This is especially true if it is getting both wetter and warmer, because that's when diseases thrive. Look for disease resistance in catalog entries, and ask your state Cooperative Extension Service for recommendations. Better yet, ask the Extension Service in a state that is near you, but historically has been wetter, with more disease problems. They will already have more experience there.
7. Look for earlier varieties than you have been used to. If your planting is delayed by wet, unworkable soil, or your season is rainier, you may need more time for things to ripen. More moisture can keep things in vegetative growth longer, too.
8. If soil is not too soggy, forking it over to introduce air will enable soil to breathe. If the soil has been submerged or so soggy that it is smelly rather than fresh and earthy-smelling, introduce live microorganisms right away to start aeration. Compost, manure, and biological inoculants are all appropriate.
9. It is tempting to work in sand for better drainage, but compost is a better choice. Sand added to a heavy soil usually produces something resembling cement. If you find the soil is still too heavy after you have worked in all the organic matter you can, pea gravel, crushed lava, rice or cocoa hulls, dead leaves, or even perlite might be a better choice to provide drainage.  Think again about what organic matter might be available to you. (Avoid sawdust, wood chips, and bark within the soil.)
10. Do a soil test, and if you need calcium, gypsum might be a good choice. It doesn't raise the pH of the soil like lime, but it does help the soil flocculate (stick in tiny clumps) which allows better drainage.
11. If evaporative cooling of the soil is a problem for your plants, avoid mulch. Apply only after soil is warm enough for good growth. If moisture continues to be a problem, leave soil open to the air.
12. If cold wet soil is a chronic problem, use hotbeds to get warm soil for your spring plantings and summer crops. A hotbed is a compost pile covered with dirt that you plant in.  It traditionally consisted of a pit filled with horse manure, with a cold frame above it. The heat generated by decomposition enabled norther European gardeners to grow crops like melons.
13. Wet soils are often nutrient-poor. Get a soil test and follow the recommendations. If you are getting much more rain than usual for your location, be aware that your usual fertility scheme may not be adequate. Plants may need more direct fertilization, either as a side dressing, drench, or foliar spray, than you are used to.

Variety recommendations:

• Asian Greens have the best performance in wet, cold spring soil of any plant I know, with the exception of Chinese or Nappa cabbage, which is an insect magnet.
• In wet heat, go with Southern favorites like black-eyed peas and okra.
• Yard-long beans like a hot wet environment.
• Of all the kales, white Russian has proved itself the most resistant to winter flooding and soggy soil. During the growing season, most brassicas like a lot of water as long as they also have good drainage. Work in gravel if necessary, or plant on a mound.
• Lettuce likes the same things as cabbage or broccoli--lots of water, but good drainage and lime. The tall rows described in #4 above work well.
• Turnips, parsnips, carrots, radishes like a lot of moisture to get started. Wet rainy conditions make germination much easier for umbellifers like carrots, parsley, and parsnips, which naturally have germination-inhibiting compounds on the seeds.
• Onions are basically a swamp plant when young.
• Celery is the most water-hungry of all vegetables.
• Hot mustards are extremely disease-resistant and resilient. Try Green Wave, Dragon Tongue, or Red Giant.
• Among herbs, parsley, lovage, chives and hyssop do well in wet conditions.
• Among perennials, Evergreen onions, chives, leaf celery, and sorrel are best bets.
• Corn like most grasses, can drink a lot of water to fuel fast growth. Give adequate spacing and watch for disease.
• Squash's big sprawling plants and big leaves can take up and evaporate a lot of water. Watch for disease--choose resistant varieties, make sure it has lots of food (compost or manure) and give it probiotic sprays to prevent mildew--a common hazard.

These have difficulties in wet conditions:

• Mediterranean herbs like thyme, sage, rosemary, savory hate wet feet.
• Basil has disease/mildew problems and will need foliar sprays of probiotics.
• Peppers
• Tomatoes except those with disease resistance. Cherokee Purple is a possible choice. There are others bred specifically for certain diseases.
• Chard and beets need very good drainage
• Melons may crack or be flavorless if over-watered