In the final article for home tomato gardening, we will discuss fertilization, common challenges and harvest. The 2019 tomato season was my favorite because my daughter discovered the joy of planting, patiently growing, harvesting and consuming my favorite vegetable. The joy on her face when she picked and ate her first tomato filled my heart. I hope you will find the same satisfaction as the 2020 growing season approaches.
Nutrient management and fertilization
In addition to initial fertilization discussed in Part II of this series, tomatoes need adequate nutrition throughout the growing season to produce well. “Side-dressing” is the application of fertilizer in a small furrow 2-4 inches to the side of the row during plant growth because all the nutrient needs of tomatoes cannot be well supplied by only a pre-plant fertilizer application.
The timing of this is application of fertilizer is often made after the first cluster of fruit has set and young tomatoes are the size of a golf ball or slightly smaller. Timing is important because young tomatoes that are supplied with too much nitrogen will produce much stem and leaf growth which can slow or reduce fruit set and yield. Often these side-dressings are repeated once a month while the plant is bearing.
One of the most important concepts for home tomato growers is calculating fertilizer needs across the whole season. The most common nutrients applied in a side-dressing are nitrogen and potassium. Nitrogen is needed for many plant growth processes, while potassium is important for many reactions in the plant and for high fruit quality. An example is provided below.
Common targets for nitrogen and potash (K2O) over a season are often around 0.5 lb./100 sq. ft. and 0.7 lb./100 sq. ft, respectively. If 3 lbs. of 10-10-10 (10% N, K2O) was added at planting to 100 sq. ft., then 0.3 pounds of N and K2O (3 lbs. x 10%) were applied.
Two subsequent monthly side-dressings of 1.5 lbs. of 6-12-12 (6% N, 12% K2O) per 100 sq. ft. beginning after the fruit set on the first cluster would provide a total of 0.18 lb. N and 0.36 lb. K2O to come quite close to N and K2O seasonal targets. Recommendations in the soil test report also provide fertilization tactics throughout the growing season.
Common challenges in home tomato production
Physiological issues
Blossom end rot (BER) involves the death of cells at the flower end of the fruit followed by decay (Photo 1).
This condition is related to inadequate calcium levels in the developing fruit. Maintaining proper pH can reduce BER risk because lime (calcium carbonate) supplies calcium while increasing the pH and making it easier for the plant to take up calcium. Calcium nitrate fertilizer can also be added to the soil as a means of preventing BER and should be applied as a side-dressing three to four weeks after transplanting, but use caution due to the possibility of oversupplying nitrogen as presented above. Providing uniform soil moisture by using soaker hoses or drip tape and mulches is also a benefit because calcium must dissolve in soil water to be taken up by plants. Tomatoes may also have less BER if they are not pruned too heavily or excessively fertilized. Sometimes, BER affects only the early fruit and clears up without action.
Misshapen fruit is often related to poor pollination, which can lead to different growth rates in areas of the fruit.
Examples include cat facing, puffiness and odd fruit shapes. Temperatures that are cool (below 50 F), especially at night can lead to poor pollination, but warm temperatures, fertilization or humidity issues can also impact pollination.
Cracking (Photo 2) can appear as concentric rings around the top of the fruit or cracking down the fruit. It can be related to variety characteristics, but is most often linked with irregular patterns in growth and/or water issues. Swings in moisture or nutrition can both lead to cracking, which is best prevented by maintaining optimum and consistent moisture. Modern varieties are less prone to cracking than heirlooms.
Harvest, handling and storage
Most home garden tomatoes are harvested fully ripe. This practice will enable full flavor development but also reduces shelf life and produces fruit that is more susceptible to damage during handling. Fruit harvested at 60-80 percent full color will ripen well in the home if handled correctly. Cherry tomatoes are often picked slightly before full maturity to prevent cracking that can occur quickly after ripening.
Most gardeners remove the fruit from the vine while leaving the calyx (small green leaves and stem) on the plant. Removing the calyx and stem can reduce fruit punctures during picking and handling. Tomatoes are best picked into shallow boxes and placed one to two layers deep to prevent damage.
Fully ripe tomatoes are generally of the highest quality when stored at room temperatures in the home and eaten within two to three days. So, it is best to harvest tomatoes from the garden when they will be consumed in a few days. If you are like my daughter, she prefers to eat tomatoes while still in the garden (Photo 3). Tomatoes are chilling sensitive and refrigeration can cause flavor loss. It is common for newer hybrid cultivars to retain a firmer texture and avoid decay for longer periods after harvest than many heirloom cultivars. If frost is on its way at the end of the season and tomato fruit is still on the plants, they can be harvested green to slowly ripen in the home. They may not be quite as flavorful as an August garden tomato, but they can be an excellent addition to a fall salad, providing a final taste of summer for the year!
For more information, please contact Shannon DeWitt, UT Extension Union County (865) 992-8038 or sdewitt@utk.edu