Hi. You may have a try by using trypan blue, may not be very accurate for quantification but it gives you good clue on membrane integrity (whether pollen grain turns out blue or not). This technique is time-dependent form my experience on different tree pollen types. So, after incubating your pollen grains with a dilution of trypan blue (eg 2 min), you should not take more than 6 min or so counting the pollen under the compound microscope.
A very fast and reliable analysis of pollen viability is provided by impedance flow cytometry. The technology is label free which means that there is no need for incubation with chemical dyes. The battery powered instrument can be used in the lab or in the field. Results are obtained within about a minute. See www.amphasys.com for more information.
Searcy, K. B., & Mulcahy, D. L. (1985). Pollen tube competition and selection for metal tolerance in Silene dioica (Caryophyllaceae) and Mimulus guttatus (Scrophulariaceae). American journal of botany, 1695-1699.
Searcy, K. B., & Mulcahy, D. L. (1985). Pollen selection and the gametophytic expression of metal tolerance in Silene dioica (Caryophyllaceae) and Mimulus guttatus (Scrophulariaceae). American Journal of Botany, 1700-1706.