Tissue analysis is the most reliable means of determining plant nutritional status. Combined with soil testing, tissue analysis can help pinpoint the source of problems and determine what measures may be needed to ensure proper nutrition of the crop. Tissue analysis samples should be collected at the appropriate time to give the most meaningful results.
Grapes: samples should be taken about 70 days after full bloom or at the start of veraison, usually early to mid-August; collect 100 leaf petioles (see Figure 1 below)
Strawberry: sample the first fully expanded leaves after renovation, usually in mid to late July; collect 30-60 leaves
Brambles: sample leaves on non-fruiting canes (primocanes) between August 1 and 20; collect 30-60 leaves
Blueberries: sample leaves during first week of harvest; collect 30-60 leaves
Be sure to collect samples to represent the entire field, not just from a few plants. Sample different varieties separately. If specific problems exist, collect separate samples from both normal and problematic areas of the planting. After collection, leaves should be rinsed gently in tap water to remove any pesticide residues and dust that might affect analysis, laid out to dry for a couple of days, then bagged in paper bags for submission to the lab. Some labs offer tissue analysis sample kits.
There are several private companies and a few universities that provide tissue analysis. A list of certified soil and plant analysis testing labs serving Indiana growers is located at: https://ag.purdue.edu/btny/ppdl/Documents/Compiled%20Lab%20Lists/PPDL-4-Soil%20Testing%20Labs-1.25.18.pdf
For desired ranges of nutrient concentrations in small fruits: https://www.uvm.edu/vtvegandberry/factsheets/tissuetest.html
Figure 1. Petioles (leaf stems) on grapevine should be collected around veraison for tissue sampling. Photo from PennState Extension