It's best stored after dessication in order to remove a lot of it's moisture. You can buy or build a dessication chamber which range from complex machines to a simple large jar with silica gel. After dessication it's best stored sealed in a near-air-tight container and inside another container. Small petri dishes (with covers) sealed with parafilm are excellent for this...then into a piece of tupperware (or similar). After that it's into the fridge or freezer. 1-2 years of good storage this way. If you want something a bit more low-tech and you're planning on a shorter storage time then you can collect tassels or knock a bunch of pollen off a tassel into a paper bag. You need to store this in consistently dry place without much moisture/humidity and give it time to dry. Once dried out it's generally good for a few weeks to a couple months without losing too much effectiveness. This method is a bit less consistent, but it's generally a good one if you have a quick turnaround for the pollen use and you can get the tassels/pollen dry + keep it dry.

I would not leave the blossoms on the tree. Collect some fresh flowers that are just starting to release pollen. Trim the anthers off the blooms onto a piece of wax paper or parchment paper, fold it over and place in a warm dry spot overnight indoors. You can then collect the dried anthers and loose pollen into a vial or small tube the next day. The pollen should remain viable for days to weeks in the refrigerator and months to years in a freezer. However, the moisture content needs to be kept low and constant, so storing the tubes in a jar with some dessicant will keep the pollen viable much longer. When its time to use the pollen, you will need to agitate the anthers to release the pollen. This can be done by tapping on the tube or grinding them against the inside of the tube with a toothpick. Then just dab it on with a small brush, or just a small twist of paper towel. Making a buzzing sound is optional.

You can dry it and freeze it for several years.Check out the site below for info. Betsy Here is a link that might be useful: Hybridizing

The reason Trospero suggested allowing the foil to warm to room temperatures before opening is to prevent it from forming water and spoiling the pollen. Once pollen gets wet, it's virtually impossible to use. Not that it may not be viable, but how do you properly spread it when it becomes paste? You want it to remain dry until it is applied. And, if your weather or house are rather humid, you may need to dry it two or three days until you can see pollen dust releasing from the anthers. We've had a few periods of humidity this spring and anthers required noticeably longer to release pollen during those periods. Good luck! Kim