Effects of an Early Warm Spring

A Fruit Tree with almost open blossoms

Monday March 25 was the first night in over two weeks that the temperature was below freezing. A news reporter stated that well over 1000 high temperature records have been broken the past two weeks. Fruit trees are in bloom or past bloom in much of the USA at least 6 weeks ahead of normal. A paper article from MN stated apple growers were struggling to get protective apple sprays on to prevent apple scab a month earlier than normal. A local home depot store had plants out side for sale.

A nursery employee and I were discussing the effects of early spring and she said the Minneapolis soil temperature was 55 degrees F. For lawns this means crabgrass is germinating. To prevent crabgrass use a good crabgrass preventer now. This is probably the best piece of lawn advice you will have if you have crabgrass. A good application will give about 100% control. However, since the application is going down about a month early, it may mean the preventive action will run out before the season runs out and you may have late emerging crabgrass this August. If you normally get 4 months control and you apply in March, it runs out in July. Crabgrass will emerge and mature in a very short time in late summer.
Forsythia indicates crabgrass is germinating.

Most plants, insects, weeds, and some diseases emerge and mature based on growing degree days, GDD. It is calculation based on how warm the day gets above a minimum temperature and each daily amount is added throughout the season. This works well in most areas. Whitney Cranshaw from Colorado State University stated “Shortly after I moved here I tried to see how well some previously proposed models worked, particularly with clearwing borers (lilac/ash borer) and pine needle scale. They did not appear to work very well at all and my thinking was that the high sunlight in our state skews GDD estimates.” In other words, bright sunlight may warm things and speed up development above what GDD would indicate.
A plum tree in bloom

The downside of very early springs is. Fruit blossoms emerge and get frozen. There is a listing of how well developed the fruit can be and how low of temperature the blossom can withstand. When the blossom bunch is tight and not really loose it can withstand down to mid to low twenties. When the blossom is opened, it freezes at about 30 degrees F. Daffodil plants can withstand a hard freeze but the blooms will freeze. Red beet plants in the garden have had enough time to have germinated and emerged. Newly emerged seedlings freeze at 28 to 30 degrees F. If it can get to the 4 leaf stage they will withstand a hard frost. The maple syrup industry was devastated this year with about 1/3 the normal harvest.

Insects may start emerging and then a hard frost kills them off. This can result in a lower number of insects to start the warm summer weather. If they emerge and there is no hard freeze it could mean a summer of bad insect problems. What generally happens is insects that fly in from the south arrive much earlier than normal. The first plants that emerge may take the brunt of early insect damage when normally they would not be bothered. Little black flea beetles will have time to develop into a bad problem before some vegetable garden crops are emerged. They may cause a real problem for early vegetables. Flea beetles will transmit Stewarts Wilt to sweet corn. This is not normally much of problem but this year could be the year when it is a problem.

Regardless of the weather now, it can change. Remember the frost free day doesn’t change from year to year regardless of the type of spring weather. A comment on a global warning article said warm winters usually mean a cool summer, that is why we call it an average temperature.

Best of Luck this very early spring,

The Garden Doc