Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Late July or early August is the time to collect leaf samples for nutrient analysis in tree fruits, grapes, and blueberries. As shoots grow and leaves age, nutrient concentrations change. Mid-summer is the standard time to sample because levels of most nutrients are relatively stable, so results can be best interpreted by comparing them to known values.
Leaf analyses is be used to diagnose nutritional problems and to identify developing problems before growth or yield is affected. Sample young plantings every one to two years and established plantings every two to three years. The whole farm can be sampled in the same years, or portions sampled on a rotating basis.
Collect a minimum of 50 leaves from 10-20 different plants throughout the field block. Select healthy leaves from the middle of this year’s shoots. If the leaves are dusty, rinse briefly in tap water and lay leaves out on a tabletop until they are dry to the touch. For vineyards, collect between 80 to 100 petioles or 30 to 50 leaf blades per vineyard block. Avoid collecting samples from leaves that have been damaged by insects or diseases or from abnormally growing vines or shoots.
For all fruit tissue samples place each sample in a clean paper bag labeled with location, block, cultivar, growth stage, and date. Send to a respected agricultural testing laboratory for mineral nutrient analysis.
These blueberry leaves are fully expanded, from this year’s new growth – just right for tissue sampling. A complete sample requires at least 50 leaves like these, from 10-20 plants.