Recent torrential rains have brought about flooded conditions in many gardens and landscapes. As floodwaters recede and folks get about the business of putting homes and lives back together, questions arise as to the safety of produce from flooded gardens, as well as potential damage to landscape plants.
If you have produce ready to harvest, the issue of food safety is best handled with caution. Clearly, if floodwater is contaminated with raw sewage, it is risky to eat the produce. Crops that can be washed thoroughly, peeled and/or boiled should pose minimal risks. However, consuming crops that are eaten uncooked, especially leafy crops, such as spinach and lettuce, is riskier, since it is so difficult to remove all of the contamination with just plain rinsing.
Newly planted seeds and transplants may not survive even short-term flooding, and seeds may have washed away. Resist the urge to replant immediately. Give the soil a chance to dry out first. Working wet soil will leave long-lasting effects of soil compaction.
Landscape trees and shrubs may be better able to withstand temporary flooding, but it is difficult to say what the long-term effect of being underwater will have on them. When soils are completely flooded, oxygen is prevented from reaching the root system. Certainly, some trees are more tolerant of waterlogged conditions, but the longer the lack of aeration, the greater the chance of root death. Generally, it is thought that most landscape plants can survive being submerged for about a week or so. Extended lack of aeration to the roots will result in root dieback, with the above-ground symptoms appearing as leaf yellowing, droopy foliage, leaf drop and, eventually, branch dieback. Waterlogged root systems are also more susceptible to attack by root rot organisms.
In areas of severe flooding, additional concerns for plant health are soil erosion, as well as deposits of additional soil and silt. Both can be damaging to the root system.
In addition to the obvious damage to plants, soils that are flooded for extended periods may suffer long-term damage. Soil microorganisms that require oxygen may be killed, and those that survive without oxygen take over, which, in turn, affects availability of nutrients for plant use. Soil structure itself may be physically harmed due to compaction of soil particles.
We may not know the full effects of flooding until long after the water recedes. And, of course, a lot will depend on what future stresses the weather brings upon our landscapes. Many properties sustained similar flooding damage last year as well, so those plants might already be in a weakened condition.
There isn’t much we can do other than wait for drier weather to prevail and allow water to drain. As more favorable conditions return, watch for signs of dieback, but don’t be too hasty to cut limbs. Branches that have lost leaves aren’t necessarily dead. Even though leaves may drop, there may be buds able to re-leaf yet this summer. Live stems and buds will have some green tissue visible. Remove only those limbs that are physically damaged or that are obviously dead. A light fertilization may be helpful to replace the nutrients that were lost in floodwater and to encourage re-growth.