Note to readers: Attached is a complete final report for FNE00-350
This project monitored and compared the growth and winter hardiness of lavender grown in the field and in greenhouses. Plants in the field were divided into plots with half of them getting straw mulch for winter protection and half receiving no mulch. One set of plants in the greenhouses was over-wintered in an unheated greenhouse; the other set was grown in a minimally heated greenhouse.
Lavender transplants were planted in the field on August 25th at two different farms. One half of the plants in each field were covered with straw mulch during the first week of December. On December 30th, a large snowstorm covered all the lavender with several feet of snow. Heavy snow cover was present for the rest of the winter. The lavender was uncovered during the last week of April. One farm had 0% survival of the lavender, while the other farm had 74% survival of the mulched plants and 20% survival of the plants with no mulch.
The greenhouse-grown plants were planted in one-gallon pots on August 25th. One farm grew the plants in a computer-controlled greenhouse with winter temperatures of 35F for a low and a daytime temperature in the high 60’s. The other farm grew the plants in a plastic-covered greenhouse that was unheated during the winter. Plants in the unheated greenhouse were mulched with straw to reduce the freeze-thaw cycle.
Plants in both greenhouses looked healthy, had new leaves, and were approximately 12” high on January 1. All the plants grown in the heated greenhouse performed very well and were 18” tall on May 15th. Only 13% of the plants survived to May 15th in the unheated greenhouse.
The growers noted that autumn weather through November was relatively warm and then December turned abnormally cold. There was over a week of single-digit temperatures in December. For field-grown plants, mulching may improve the ability of the plants to survive the winter, but if the plants are in a field that is highly exposed, mulching may not provide enough protection against the harsh weather. The cooperating farmers believe that lavender that is rated for zone 5 may not fare well during harsh winters.