If it's good and dry, you can freeze it. The freezer is better than your fridge freezer as it keeps longer. I haven't frozen plum pollen, but chestnut pollen keeps at least several years in the deep freeze. Have you the whole anther or just the pollen?
Jocelyn

I have the whole anther, it had rained the previous day and it was not easy to just get the pollen. At this point I only want to hold on to the pollen for a few weeks for that time frame is the freezer the best?

Yes, anything over about 6 days the freezer is better. Frozen pollen works well, it needs only a few minutes to defrost. One problem might be getting the anthers to open so you can get at the pollen itself. What did they look like? Open on the seam or still closed?

I thought pollen lasts forever. That it's not alive. What I see is a dust like substance that remains for years.

Wrong?

Pollen is alive....it's just so small it LOOKS like dust. Pollen must germinate and send a pollen tube down into the ovule to fertile it and make a seed. Dead pollen equals no seed, no fruit.

Jocelyn

In general, each pollen grain is made up of an outer resistant shell that houses the genetic material of the plant (equivelant to sperm in animals). The genetic material has a shelf life of days to months depending on the environment, but the outer resistant shell can be preserved for hundreds of millions of years. Fossil pollen is used in many geologic studies either as age indicators or environmental indicators (or both).