This is a week of transition in more ways than one here at Wellfield Botanic Gardens. Ahead of our May 22nd reopening, we began Member Appreciation Week on May 15th, granting garden members early access to our thirty-six acre campus. Second, we begin transitioning from our spring display of tulips to our summer display of annuals. This week, we removed tulips from the Annual Garden and Visitors Cottage, and we received shipments of annuals from growers in Michigan. Third, we transitioned from the cool, dry weather pattern we were under for much of late April and early May to more seasonally appropriate temperatures and rainfall.
This has been the most gradual spring warm up I have observed in the four years I have been tracking growing degree days here. I estimate we are currently about two weeks behind the five year GDD average.
There are pros and cons to this pattern, as in any horticultural activity. A juggling act in any year, this year’s slow warming has allowed us to work at a more measured pace as we complete construction of our Island (Japanese) Garden. Some years, biology is moving along at such a pace that some garden tasks just get set aside due to lack of time or missed windows of opportunity. Not so this year. This has been the most stress-free spring I can remember due to our excellent garden staff (including our two new full-time Lead Horticulturists, Amy and Patrick) and the garden’s slower start up. The early cooler, dry weather suppressed most garden pest and disease growth/development, relieving some burden that comes with an early warm up.
The slower rate of development comes with downsides, several of which I am sure you have experienced yourself. First, the late series of severe frosts over the past week really did a number on some plants. Frosts are not unusual this time of year, but the severity of the frost temperatures in some parts of Michiana was. Here, magnolias took the usual hit, along with big leaf hydrangeas and some birch. Plants respond differently to late spring freezes depending on their genetics, site conditions, stage of development and stress level. It can sometimes take many days for the damage to be evident to the naked eye. Most woody plants will recover and press on. Herbaceous plants may be a different story. Fortunately, I have observed very little herbaceous damage here except to a few transplanted hostas already under stress. Time will tell, of course.
I usually do not panic when I see frost warnings issued at this point in the season. I watch the thirty day forecasts to see the night temperature trends compared to averages. The trend information helps me prioritize what activities need to be moved up or down on my to-do list. I take a close look at my site and predicted conditions when a threat of late severe frost is looming. Frost severity in the garden is all about microclimates. Frost can only form when the air temperature near the surface of an object is thirty-two degrees or colder (depending on relative humidity levels). Just because the night temperature is predicted to sink close to the freeze mark does not necessarily mean you are going to get frost. Cloud cover, wind speed and the lay of the land all play important roles. Wellfield experiences fairly good airflow even on the calmest nights, and with most of my annuals sitting on tables waiting to be planted, I often do not protect this plant material. The air temperature a few feet off the ground can be just high enough to prevent frosting. I often tell people trying to determine where they might experience frost in the yard to ask themselves where in the yard does the snow melt last. This will give you a clue.
The second big drawback with the unusual cool crawl has been delayed growth of cool season vegetables. Here at Wellfield and at home, all direct sown and transplanted vegetables are developing SLOWLY. This growth delay will push harvest dates back and will affect warm season crop plantings like beans, peppers and eggplant, which require the space currently occupied by lettuce, peas and radishes.
The weather pattern I fear most is a cool early spring that rockets to a very warm late spring with summer-like temperatures and moisture. Garden tasks are compressed together under such conditions, because one is left juggling spring work with the sudden demands of summer care. The expected warmer, wet weather over our area will greatly accelerate plant growth in the coming couple of weeks: be prepared. Be prepared for insects to bug out all over in some cases. Be prepared for the sudden flush of germinating summer annual and perennial weeds. Be prepared for a compressed gardening timeframe as summer temperatures are really just around the corner.
Hopefully, the cool weather is in the rearview mirror for good. No matter what happens over the next couple of weeks in the garden, it is still a positive change, something we all could use right now.
Josh Steffen, Horticulture and Facilities Manager