With many things in bloom, the uncharacteristically cold temperatures have had an effect.
My thermometer hit 23 degrees F on Saturday morning and 29 this morning. Outside, the leaves on Crape Myrtles, hydrangeas and Canna lillies, that had been doing so well, have been killed and the beautiful blooms on the Rapheolus and wysteria have also been killed. So the biggest problem now is to decide what effect it has had on the garden.
In general the effect will be cosmetic only. Early blooming shrubs have lost their flowers but the leaves are not yet out, so they will continue to grow again as soon as the temperatures mediate. For new growth already on trees and shrubs it is going to take a little longer. The shrubs will have other leaves that are put out, but the ones already out there, or close to maturing will be lost. It will likely take a week or two for the new leaves to show, so this event has put things back to perhaps mid March. Cannas and other perennials that were already up and growing, will likewise loose what is out there and have to start again. These need to be trimmed, so that the rotting dead foliage is pruned away.
Truly borderline perennials though such as fruit sages (Salvia elegans) are more of a problem and will have to be watched to see if they have tolerated the frost of have been lost. The critical thing to look at will be how much top growth it had acheived already. All the top growth will be lost along with the ability to photosynthesize, and thus these may not recover.
More of a concern are those trees where the fruit is the prime reason for growing them. Depending on which stage of flower, pollination and fruit set that the tree is in, will determine if the fruit will be lost. Clearly if the flower has been frozen off, then pollination cannot occur and thus this year that tree will be barren. The days immediately after pollination are able to stand some frost. How much frost and freezing is determined by the species and cannot be generalized. If you think your tree was affected, look at the state agricultural site and see if they give a chart for fruit set temperatures such as this one for blueberries or try plugging in the fruit name + freeze data into your browser.
Late frost are normal, but a really hard freeze is not so common and will be the cause of much concern over the next few weeks.
