By Bryan Hager, Crager Hager Farm, Carrollton, Ga.
Everybody wants lettuce to go with their tomato sandwich, yet those two crops do not easily grow at the same time in Georgia. Lettuce and many other salad greens are cool season crops that do not fare well in our hot, humid summers. At Crager Hager Farm we have been working to extend the season of salad and cooking greens throughout the year. We are growing in the field and high hoops. I will share what we have done to extend the seasons for cool season greens.
Our farm is in the Piedmont, due west of Atlanta. We have heavy clay on the hills and sandy clay in the bottoms. Our summers are long, hot and humid. We have four 30 by 60 feet high hoops and another half-acre up on the hill. We also have 3 acres in a bottom along a creek about 1 mile from the farm. We grow mid-sized and large cut leaf and whole heads. We pride ourselves on the taste and durability of our produce. Our customers regularly tell us the greens or lettuce they bought from us a week ago are still good.
Growing salad greens into the summer brings with it a host of problems including pests, diseases, bolting, and bitterness. It can be more difficult to get plants germinated and transplanted. Once they are grown they can wilt quickly after harvest.
Here is what we do beginning with the soil. In the high hoops and other growing areas on the hill we have heavily amended our clay soils to get the soil organic matter up to 5-8%. Beds have been double dug to at least 18 inches. Potassium, phosphorus and calcium are all in the very high range on standard soil tests. We use leaf mold, granite fines, our own compost and some bagged organic fertilizers. I do soil tests each year to make sure I am keeping the correct ratios of calcium to magnesium, calcium to potassium and phosphorus to potassium. We use UGA Extension for annual soil testing, and A & L Labs for occasional complete tests. For each planting we add a high nitrogen fertilizer, usually pelletized feather meal.
The soil in the bottoms is sandy and does not hold nutrients well. Each fall I apply chicken litter and some bagged fertilizers. I have also applied commercial compost and granite fines. I am using cover cropping and thick hay mulch for parts of the rotation to build up the organic levels.
To control pests I have a diverse landscape, including rows of aromatic herbs planted on each side of the high hoops(catnip, peppermint, lavender, oregano and tansy). Flea beetles and various caterpillars are regular problems which I control with Pyganic and Bt, respectively. Slugs are occasionally a problem and I use diatomateous earth for them. I use swiss chard as a trap crop planted slightly away from the other crops.
Bottom rot on the lettuce is the only disease problem I have experienced. In order to control diseases I minimize the amount of nitrogen fertilizer I use and keep the other major and minor nutrients high.
Bolting is genetically planned into crops based on the number of sunny days, so I buy slow bolting seeds for the summer crops. I buy most of my seeds from Johnny’s and they have good information on bolting characteristics. One caveat on Johnny’s, their lettuce seed packets do not have variety specific information and they are constantly changing varieties in the catalog. So if you save seed for another year write the variety info on the seed packet when it arrives.
Bitterness is a result of the plant responding to stress or beginning to bolt. The stress can be heat, drought or insect damage. Soil temperature seems to be more important than air temperature. To manage heat in the high hoops I take the plastic cover off the ends, roll down the sides and put a 50% shade cloth over the top. One hoop house is adjacent to my woods to provide shade and cooling in the afternoon (I have to dig a trench around it each year to cut the tree roots trying to reach the water in the hoop house). In the house where I am growing cut and come again lettuce and some other greens, I have misters that spray for a few minutes each hour during the day. The misters (from Dripworks) are mounted into pvc pipe that are put on stands in the beds. In the field I plant some of the more durable crops, like kale and chard, on the east side of a bean trellis and mulch them with hay. Head lettuce is planted through white on black plastic mulch and covered with shade cloth on wire hoops. The shade cloth goes to the ground to discourage insects and keep the crops clean.
We use drip tape for irrigation, generally three runs per bed. In the high hoops the irrigation is on automatic timers and runs nearly every day for 20-50 minutes depending on season. In the fields I do not have the automatic timers so I soak for 2-4 hours once or twice a week. In the high hoops we plant closely together so the crops shade the soil to reduce evaporation. These beds are 36 inches wide. We put in six rows of spinach at 3-4 inch spacing in the rows. Lettuce is six rows with 4 inch spacing for cut leaf and 6 inch spacing for small head. Arrugula has 12 rows with 1 inch or less spacing. Asian greens, chard and kale will have four or six rows depending on the size of leaves I am trying to grow. Micro-sprinklers could be a good option for watering greens, especially if you can set the timer to run in mid-morning and early afternoon.
I transplant all of my lettuce and greens, except arugula. I start all my plants and use fluorescent lights in an enclosed room for germination. The lights can generate a lot of heat so I run them at night with a vent fan pulling through the cooler night air. I transplant late in the evening or at night with a headlamp or work lights. This has helped a lot to get plants through the shock of transplanting in hot weather.
I have spent a lot of time and effort to grow the crops so I want to make sure they survive harvest in the best shape possible. I harvest early in the morning when the air is coolest. Before my harvest crew arrives, I walk the beds and taste pieces of the leaves to make sure they have not turned bitter. All of the cut leaves are grown on the hill where I can take them to the wash station to be dunked in chilled water (we make our own ice blocks), then spun dry in a modified washing machine. Head lettuce harvested on the hill is placed in plastic mesh crates and put in the walk-in cooler. If it has dew on it, I will leave it in the cooler without any covering to speed up the chilling, and then after a few hours I will cover with a towel. If it does not have dew, I will sprits it with a water bottle. The bottoms are farther from the wash station, so head lettuce harvested in the bottoms will be put in a tub with crushed ice. When I get back to the hill I shake the ice and water off and put in the plastic mesh crates. If I think the head lettuce might have more than an occasional slug in them, I will dunk them in water and shake them before putting in the plastic crates.
I believe our products hold up well in the customers’ refrigerators for three reasons. We do not use excess nitrogen fertilizer that causes plants to take up excess water. We chill the crops soon after harvest. Also, we try to keep the leaves moist but not wet.
Growing great vegetables begins with knowing what the ideal environment is for the crop. Lettuce, spinach and most Asian greens love very fertile soil with lots of organic matter and high water holding capacity. While the surface of the soil should be allowed to dry out between waterings to reduce mold problems, the soil should stay moist. Air temperatures should average around 60-F. In order to provide good storage quality, the air temperature when harvesting should be between 35 and 40-F with a light dew on the plants. We can’t provide these exact conditions on our farm, but we are trying to come close. You can too.