my neighbor says that she spreads her mix on a cookie sheet
and bakes it in the oven for about ten munutes. I have not tried it but she claims it works

That sounds like something I will try... than you!!

Thanks for the idea: I just tried microwaving the bird seed in a glass cake pan; because the seed was dry I added a glass of water in the microwave oven so the seeds wouldn't burn/catch in fire. Put some of the 'zapped' seed later in some water to see if indeed it would still germinate! Many years ago I tried to 'sterilize' some newly purchased flour in the microwave without a glass of water & it caught on fire!; I now try to freeze things like flour for a week or two when I purchase it to kill off any of those awful weevil eggs that hatch later in the sealed bag!:( Will the nutritional value of the seed be lost after microwaving? Just wondering ...!

when i lived down south we kept all our flour and oats and cereals in the freezer to not only stop weavils but also they keep fresher cause the oil or fat in them does not go stale as easy. Also coffee. I know cooking food to eat in the microwave is supposed to have better nutional value than boiled but i don't know about baking the seed for value. I'm just guessing they are after the protein and starches for energy more so than for vitamins or nutrients
as the birds eat tremendous amounts for their size cause they burn so much energy. I guess i'll google the subject sometime and see what comes up.

well i found thousands of pages on google about sterilizing bird seed. Both pro and con. The most popular way to to nuke it in a paper bag. They mostly say if you cook or bake it don't over roast it or you affect the nuttitional value. Just heat it all the way through to sterilize it.

dklucius:

For lack of more freezer space, I also freeze flour, cereal,cornmeal, etc. when I buy it for two weeks or so but then take it out & store it at room temps. It seems to do the trick that way also!

I'd heard that microwaving uses moisture to heat & that was why my flour caught on fire so I always now make sure there is something like a glass of water in the oven when I heat dry products. I like the idea of microwaving the bird seed though & got no germination of seed I placed in water after the microwaving so I guess the seed was no longer viable ... good! The birds at the thistle sock sure scatter though & make a mess on the patio even though it doesn't germinate!

One of the simplest solutions to seed mess is to feed seed that birds in your region readily eat. Many seed mixes have filler seed, such as wheat, that birds don't prefer so they throw it out of the way so they can get to the stuff they do like. Feed seed they like and the birds will waste less.
I don't know what type of feeder you're using but some seeds work best scattered on the ground. Corn in any form is one as are millet and milo. Milo, the little round orange basketball looking seed, is one of the most common filler seeds used and one of the least bird preferred seeds there is. Yes they will eat it but usually only after all the good stuff is gone. That being said, doves of any type will eat milo but what won't they eat? Rodents also like milo and milo loves to grow in gardens and lawns.
Millet is a very well liked seed but it is best fed out of a tray of some sort or directly on the ground. Most birds that like really like millet prefer to eat low or on the ground, native sparrows and juncos for example.
Another way to avoid shell mess or sprouting issues is to feed a hulled seed. Hulled seeds have had their outer hull removed by mechanical means. When you remove a seeds hull it won't sprout, at least 99% of the time. Also, no hulls = no hull mess!
Hulled seed and seed blends do cost more than regular seed but you get more edible seed per the same amount of weight. 25 lbs. of hulled seed is 100% edible whereas 25 lbs. regular seed (with hulls on) is not that high and you're buying hulls that will be thrown on the ground. I'm not saying the 25 lbs. of regular seed is not edible, I'm saying that part of that weight is made up of inedible hulls.
Lastly, you get what you pay for.
Cheap seed is cheap seed. Cheap seed is often old or stale. Birds will waste a lot of it looking for more palatable seed which may or may not be in there.
Cheap seed often is bulked out with filler seed/grain that will wind up on the ground. It's also often bulked out with gravel. I'm not kidding. A large discount chain whose name starts with a "w" and ends with a "t" often sells seed which contains fine gravel. I inquired about it and was told, "Everyone knows birds need rocks in their food". Well, that wasn't "grit" and I'm not feeding parakeets.
The points of this harangue are feeding quality seed that is mixed for your regional birds is the easiest way to lessen waste and mess. If it's within your means feeding a hulled seed/blend will lessen it even more. If possible, avoid blends containing corn or milo. If you do feed these, feed them on the ground instead of putting them in a feeder as they are more readily consumed by ground feeding birds.
Buena suerte!