Usually, I worry, write and think about the effects of severe weather in July and August, which is when we get the hotter and more humid days that generate big thunderstorms and fierce weather systems that can be damaging to crops during harvest. But the weather over the past couple of weeks suggests that there might be some value in considering the impact of severe weather during spring and early summer.
Severe weather comes in many different forms. It can include (but not be limited to):
- High winds, sometimes ferocious and damaging
- Heavy rains
- Excess water accumulation (extreme runoff and flooding)
- Hail
Each of these can cause problems when we have crops close to harvest maturity, but these same weather events can cause trouble for our emerging, young, and developing crops.
Wind:
Strong, gusty winds often come at the leading edge of a storm front, as they are associated with differences in temperature and air pressure. The bigger the difference, the stronger the winds.
Sustained strong winds can affect pollination (including restricting some pollinator activity), can cause physical/mechanical damage, such as rubbing or abrasions (leading to wounds that are open doors for some diseases), and can potentially cause flowers to be lost if they are at a sensitive stage of floral development. Small, delicate seedlings can be bent and broken by strong winds or may be damaged by flying debris. Persistent winds, combined with heat and dry conditions, can potentially result in elevated moisture stress in some plants.
Strong and gusty winds can cause similar damage, but can also cause branch breakage in woody plants, can increase flower loss, and can cause damage to delicate seedlings.
Strong winds can also damage protected crops and the structures around them. In garden centres, it is easy for potted trees and shrubs to be blow over and potentially damaged, if they are secured in some way. I have vivid memories of picking up trees repeatedly in the garden centre where I was working because we did not have such a system.
Winds can also do a number on greenhouses or sales structures. I remember coming to work one morning decades ago, to survey the wreckage of one of the garden centre houses after plow winds had ripped through. Yuck.
Heavy rains:
The force associated with heavy rain can cause physical injury and can knock off blossoms and foliage. In some ways, early season heavy rains may cause less overall damage to smaller plants, theoretically because there is less plant material for the rain to contact. However, small plants may be broken or irreparably damaged, as they cannot absorb the loss of leaves and stems that a larger plant might.
Heavy rains can potentially introduce and spread some diseases. This is certainly the case with bacterial pathogens, such as Fireblight. I have seen cases where the disease incidence and severity were dramatically increased after a heavy rain, as the physical wounding, combined with the splashing of the pathogen, got things moving in the wrong direction. I should note that this would only really be a factor provided the pathogen was present in some amount at the time of the rain.
The splashing of soil onto plant parts may result in the introduction of soilborne pathogens.
Flooding:
Flooding (associated, of course, with the heavy rains) can cause some issues in early crops. If the water is not removed or saturated conditions are not corrected quickly, plants can suffocate and die, seeds can rot, and seedlings can die.
Runoff:
Nutrients may be lost from the soil due to heavy rains, flooding and soil running off. Excess water can leach out mobile nutrients, resulting in deficiencies later in the season. Loss of soil from water running off can also expose plant roots and destabilize plants.
Hail:
While hail is not necessarily typical in early season storms, it is always a possibility. Hail can do similar damage to heavy rain, although more visibly. Small plants, seedlings and tender plants are all prone to injury from hail strikes.
How do you react? (a.k.a. what do you do about severe weather?)
With any severe weather situation, the natural response is to leap up and DO SOMETHING, right away. Other than correcting flooded or saturated soil conditions by removing water, or cleaning up larger debris, the best thing that you can do is wait. Assess crop health and immediately visible damage at the time of the weather event, to form a baseline of what things look like. Then wait a 3-7 days for things to settle. You will be able to see what things are truly damaged and what might recover. Prior to that, you are just guessing. Being patient is hard, and feels like doing nothing, but being patient is an active response.