Sunday, June 9, 2019 By: Ask A Master Gardener

Coping with Too Much Rain and Flooding

Coping with Too Much Rain

Allen Robinson: Ask A Master Gardener
Sunday, June 9, 2019
Q: The amount of rain that we have received lately has been considered by some as unprecedented. What effects will this have on my garden and what should I do about it? Rebecca T., Tulsa
A: While most of us love the rain, too much of a good thing is rarely a good thing. So you are correct — too much rain can wreak havoc in the garden, which can happen in some rather unsuspected ways, such as:
Perhaps the biggest problem is that too much rain can actually drown plants. Water sitting in the soil actually fills all of the subsurface voids that would otherwise contain essential oxygen for root and plant growth. When that happens, plants are simply not able to respire/breathe and, therefore, will eventually suffocate. Carbon dioxide and ethylene gases can also accumulate, both of which can be quite toxic to plants.
Symptoms of waterlogged soil include plant leaves turning yellow, turning brown or wilting suddenly. Short of waiting for the soil to dry out, there’s not much you can do to reverse the situation. A couple of tips to help: 1) Pull back the mulch from around plants to facilitate the drying process and 2) carefully stab a garden fork into the ground to help needed oxygen reach deeper into the soil.
Too much rain can actually leach essential nutrients out of the soil, especially nitrogen. Nitrogen easily moves through the soil with just simple watering (potassium and phosphorus do not), and heavy rains just exacerbate the situation. So once the soil dries out a bit, consider applying a fertilizer that is high in nitrogen. Common types are Ammonium Sulfate (20-0-0), Ammonium Nitrate (34-0-0) or Urea (46-0-0). Milorganite and Osmocote are also good choices. Or simply top-dress plants with compost, which contains all of the essential ingredients.
Splash down
Mud that splashes onto leaves and stems often harbors fungal spores. If this occurs, simply wash the entire plant with a gentle mist. On plants that are particularly susceptible to fungal diseases (e.g. roses, tomatoes), consider applying an all-natural fungicide as a preventive measure.
Tread lightly
Be careful where you walk. Your weight (regardless of what it is) can cause severe compaction in wet soils, which is the enemy of plants. If you have to work in the garden, first, place a board on the ground, then walk on it to minimize compaction. Walking in wet soil can also hasten the spread of fungal diseases.
Pollination can also be affected by heavy rains. This is because pollinators have a tough time flying in the rain and heavy, wet pollen simply isn’t as effective at doing its thing. There’s not much you can do to remedy this problem short of waiting for the weather to change.
Grass, anyone?
We have all been frustrated during those times when frequent rains make it impossible to get out and mow our lawns. And by the time it is dry enough to mow the grass, it’s overgrown. One way to conquer this is to double-cut the grass. Raise the mower deck to its highest notch, mow, then drop the deck height to your preferred level and mow again. The second mowing should be done in a different direction to the first mowing.
Now, we just need to find out who overdid the rain dance.
Get answers to all your gardening questions through the Tulsa Master Gardeners Help Line at 918-746-3701, at the Diagnostic Center, 4116 E. 15th St., or email
Garden tips
  • Renovate overgrown strawberry beds after the last harvest. Start by setting your lawnmower on its highest setting and mow off the foliage. Next, thin crowns 12 to 24 inches apart. Apply recommended fertilizer, pre-emergent herbicide if needed and keep watered.
  • White grubs will soon emerge as adult June beetles. Watch for high populations that can indicate potential damage from grubs of future life cycle stages later in the summer.
  • Fertilize warm-season grasses at 1 pound of nitrogen per 1,000 square feet. Don’t fertilize fescue and other cool-season grasses during the summer — wait for fall. Nitrogen, the first of the three numbers on all fertilizers, is very water soluble. So if you fertilized before the recent rains started, much of it may have been washed into deeper soil or drain water. After the rains have passed, consider re-applying a nitrogen-only fertilizer at the rate indicated above.


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