How to cope with frost after spring buds

So much for an early spring! The cold winter storm that plowed through Northern California this week reminded us: We’re still in winter!

We gardeners can see the damage on tender new growth as well as frost-sensitive plants. Some damage is obvious while other issues will show up later.

According to the National Weather Service, downtown Sacramento got down to 34 degrees in the wee hours of Feb. 18 and again on Feb. 19. Pre-dawn temperatures will continue to flirt with freezing for at least two more nights.

Following spring-like temperatures in the upper 60s and low 70s, this sudden plunge in temperature can kill tender new growth – or transplants altogether.

Signs of frost damage are already prevalent in Sacramento gardens. That chill killed new sprouts and browned transplants as well as burned tender growth on roses and other shrubs that were pushing out shoots.

It’s not unusual for Sacramento to see February frost. But when it follows warm weather (and spring growth spurts), it can cause long-term damage.

Roses, for example, can develop stem cankers – little ulcers on the outside of canes where cells have ruptured. It may appear as purple splotches on fresh green growth. These cankers can take weeks (or even months) to fully develop, but eventually those little splotches lead to the cane dying back.
This is not a late frost – not even close. In 2022, Sacramento saw frost April 12 – more than three weeks after our historic “frost date,” the latest average date of below freezing temperatures.

Besides the cold and frost danger, plants got a cold frontal assault from the recent storm, too. Some areas saw hail, some even had snow.

According to reports, snow on Thursday reached all the way down to 1,000 feet in the Sierra foothills. Auburn, Grass Valley, Amador and other communities saw at least a dusting with slushy accumulations on lawns and parking lots.

Hail damage depends on the size and intensity. Often, it leads to little nicks (especially on young strawberries or other forming fruit) or pokes holes in large leaves. It can devastate the blossoms on stone fruit trees.

Most everybody got a lot of rain. Sunday through Tuesday (Feb. 15-17), Sacramento received more than 2.5 inches. Our soil maybe saturated – leading to other issues.

Another storm is headed our way, says the weather service. With strong winds, this incoming system could bring another inch of rain, starting early Tuesday.

How can you protect your tender transplants from this unstable winter weather? Here are some possibilities:

* Use a plastic milk or water jug as a mini hot house over a new transplant. Cut out the bottom and leave off the cap. This do-it-yourself “hot cap” will protect the transplant from wind chill and frost danger.

Keep those protective jugs handy for frosty nights. They can be removed during the day (especially if high temperatures heat back up to the 70s) or left in place.

* In the afternoon before a frost forecast, deep water tender plants; that extra moisture keeps the ground warm enough to avoid damage.

* Also, deep water citrus trees, which are bearing ripe now and beginning to bloom.

* Make sure to mulch your veggies. Those wood chips or leaves act like a blanket over plant roots, keeping them moist and cozy.

* Leave frost damage on the plant; it can prevent further injury. When temperatures warm up reliably in late March or April, trim off the damaged foliage from shrubs. Frost-burned transplants may need to be replaced.