Producing Lettuce Year-Round

 

 

 

 

 

 

Consumers continue to seek out locally grown produce, in winter just as in summer. Producing head lettuce throughout the year can help meet that market demand, and allow growers to maximize production and income from their high tunnels. New cultivars of lettuce with good heat and cold tolerance, as well as ease of harvest, are now available to help growers who wish to produce lettuce year round.

 

By "head lettuce", we are definitely not referring to iceberg lettuce! Rather, head lettuce refers to several types of lettuce that are grown to full size, and harvested one time as a single head of leaves. This is in contrast to mesclun or baby lettuces which are grown in a solid "lawn" and harvested as individual small leaves, once or multiple times. Dr. Jett's research shows that bibb, romaine and Batavia types of lettuce are good choices for year-round production and marketing because they are popular with consumers and perform well under our growing conditions.

 

 

Based on several years of research at multiple locations, Dr. Jett's recommendations are as follows.

 

 

Transplants allow for earlier and more uniform harvest compared to direct seeding. Pelletized seed is easier to handle and more uniform than non-pelletized. Use 96 or 128 cell trays for best results. The optimum temperature for transplant growth is 65-75 degrees F; at this temperature range, transplants will be ready in approximately 28 days. Fertilize seedlings in the flats weekly using a 200 ppm nitrogen solution.

 

 

From March 1 through October 1 (or later if weather allows), stagger plantings by 10-14 days. Note that later plantings will grow more slowly in the fall months, and very slowly through December and January. The days from transplanting to harvest will range from 50-75 days, with length of time increasing in colder months. Crops for winter harvest should be planted before November so that most of their growth is completed before the coldest months.

 

 

Optimal spacing for bibb lettuce is 6-8 inches within the row and 8-12 inches between rows. For romaine, use 12 inches within and between rows.

 

 

To help modulate soil temperatures through the year, use black plastic mulch for early spring, fall and winter lettuce crops, and white or reflective mulch for summer crops. Watering is best done through a standard drip irrigation system using a medium flow tape, 2-3 lines per bed. Generally, irrigation is not needed in the coldest months.

 

 

The optimal soil pH for lettuce production is 6.5-6.8. Potassium and phosphorus fertilizers should be applied before planting, following soil test recommendations. Apply approximately one pound of nitrogen per 1,000 square feet prior to planting, then apply 0.5 lbs N/1000 square feet as split applications through the drip system over the 4-6 weeks of crop growth.

 

 

Managing the temperature in the high tunnel is key to successful year round production. The optimum growing temperature range for lettuce is 65-75 degrees F. Most cultivars will grow if the temperature is above 40 degrees. Above 85 degrees, bolting and tipburn can develop, but much less so in heat-tolerant cultivars. High temperatures in summer can be managed by venting and the use of shade cloth (47-50% shade). Row covers, supported by hoops, should be used when temperatures fall below 40 degrees. One layer of 0.8-1.0 oz row cover is recommended for temperatures down to 30 degrees. Two layers will protect the crop down to 20 degrees, and three layers are needed below 20 degrees. Row covers should be removed in the morning, temperatures permitting, and replaced three hours before sunset. Avoid keeping the lettuce under the row cover for extended periods of time or tipburn may develop.

 

 

Extensive trials were conducted to determine the most productive cultivars for different seasons. Dr. Jett recommends the following cultivars for high tunnel lettuce production. Batavia cultivars, also called "summer crisp", resemble bibb types, and are noted for their heat tolerance. Salanova(R) lettuce cultivars are a recent introduction, and have a unique head structure. When cut just above the growing point of the crown, these lettuces fall apart into numerous small, ready-to-eat leaves resembling mesclun or baby lettuce.

 

 

 

A number of pests were observed in high tunnel lettuce trials, including aphids, grasshoppers, sclerotinia drop, and rodent damage. Control measures include good sanitation, insect exclusion screening, trapping, and biocontrols. Detailed recommendations can be found in the NYS IPM Production Guide for Organic Lettuce (see below).

 

 

An analysis of production costs and revenue was conducted to determine the profitability of head lettuce production in a high tunnel. Based on a crop size of 1782 heads, sold at $2/head, net revenues were $2.58 per square foot of high tunnel space. Considering that one high tunnel can produce multiple crops in a single year, this compares very favorably with other high tunnel crops.