Tomato performance in the field, the greenhouse and the high tunnel is strongly dependent on good nutritional management. While a soil test is helpful in determining preplant fertilizer applications, an excellent way to know the status of nutrients in tomato plants on an ongoing basis is to conduct a simple tissue test of the tomato leaves. Especially as the spring approaches and tomatoes are growing rapidly, growers can lean on tissue testing to help guide injections of soluble fertilizers to meet plant needs. Maintaining optimum levels of nutrients in tomato plants is critical to maintain high yields and continuous harvests.
The tomato tissue test is based on collecting a sample of the most recently matured leaves on the plant, including all of the leaf blade and the leaf stem. Generally, this leaf is the 3rd to 5th leaf from the growing point of the plant. Include 8-10 leaves for a good sample, avoid leaves that are diseased or insect-damaged, and sample different varieties separately.
The tissue test is helpful to identify the cause of visible nutritional problems; in this case, collect a sample of normal leaves and a sample of leaves exhibiting the problem for comparison. Collect the tissue samples at first bloom, early fruit set, at first ripe fruit, and during harvest (weekly if possible). Once collected, dry the leaves for several days, place the leaves in a paper (not plastic) container, and ship the leaves to a laboratory for analysis. The tissue nutrient levels are compared to nutrient "sufficiency ranges" (Table 1), and any shortages are noted on the tissue test report. Growers can then adjust fertilizer injection rates and timings to address any nutrient shortages.
Table 1 Nutrient sufficiency levels in tomato tissue samples1
| Elements | Sufficiency Range |
| Nitrogen (N) | 4.00-6.00% |
| Phosphorus (P) | 0.25-0.80% |
| Potassium (K) | 2.50-5.00% |
| Calcium (Ca) | 1.00-3.00% |
| Magnesium (Mg) | 0.40-0.90% |
| Sulfur (S) | 0.30-1.20% |
| Iron (Fe) | 40-300 ppm |
| Manganese (Mn) | 40-500 ppm |
| Boron (B) | 25-75 ppm |
| Copper (Cu) | 5-20 ppm |
| Zinc (Zn) | 20-50 ppm |
| Molybdenum (Mo) | 0.6-30 ppm |
1 University of Missouri Soil and Plant Testing Laboratory
The University of Missouri plant testing laboratory (https://extension.missouri.edu/programs/soil-and-plant-testing-laboratory/spl-plant-analysis) provides tissue testing services. The charge for a regular analysis (levels of N, P, K, Ca, Mg) is $17; a regular analysis plus micronutrients is $23. Contact your local MU Extension office for assistance in collecting and submitting tomato tissue samples. A video on tomato tissue sampling is posted at https://www.youtube.com/watch?v=jj5yzXWeA1c. The lab can be reached by phone at 573-882-0623 or by mail at:
Soil and Plant Testing Laboratory
23 Mumford Hall, University of Missouri
Columbia, MO 65211