Hi Highlander, "So, if they aren't coming up this year, how long will they last in or on the soil or mulch? Will the seeds dropped last year come up next year or in future years?" A very small percentage of zinnia seeds survive as "volunteers" the next Spring, but I wouldn't expect any of those seeds to make it to a second year. "That brings up question 1: How to prevent powdery mildew on zinnias?" A non-toxic way is frequent sprays of a product called GreenCure. It is basically potassium bicarbonate with a proprietary wetting agent. You have to spray it fairly frequently because it is water soluble and rains or even heavy dews can wash it off into the soil, where it acts as a source of potassium nutrition. I suspect it also foliar feeds some potassium. It is safe to use. It is better than using sodium bicarbonate. I breed zinnias as a hobby (see the "It can be fun to breed your own zinnias" message thread), and three years ago I found a tubular petaled mutant that I wanted to preserve as long as possible, providing pollen for crossing with other zinnias and developing seeds of its own. To prolong the life of that zinnia plant right up to our killing freeze, I applied Bayer All-in-One Rose and Flower Care as a drench applied about every two weeks, and it prevented Powdery Mildew and other foliage diseases on that zinnia specimen right up until it was killed by a hard freeze in late Fall. It is fairly expensive, so I don't use it routinely on my zinnias. But since it is systemic, it isn't washed off by rain and it spreads its protection to new growth, unlike surface sprays. It is not for organic gardeners, because it does contain "chemicals". I foliar feed my zinnias with Miracle-Gro products, and I am experimenting with adding some Physan 20 as a wetting agent and, since it is a bactericide and fungicide, among other things (some hospitals use it in their mop water), it may tend to prevent Powdery Mildew. This isn't the "season" for PM yet, so I won't know until this Fall if it can play a role in preventing PM and other diseases on my zinnias. But so far, so good. ZM (not associated with any product or vendor mentioned or linked)

If stored properly, seeds can be stored for decades. "Proper" storage means 5-8% humidity and frozen. I try to keep mine lined up in paper coin envelopes inside of an airtight tackle box with some silica gel, and then in the deep freeze. But if I'm re-arranging or actively planting seeds, they're in the fridge for a while. So your seeds are doing quite well for fridge storage with unknown humidity, but that is not uncommon. I'm still using lettuce and brassica seeds from the early 1990s.

"It is understood that freezing is an excellent seed preservation strategy. BUT, the seed must be COMPLETELY dry before freezing." I agree. With very few exceptions (for seeds which won't survive freezing by nature) if seeds die when frozen, excessive seed moisture is usually the cause. The problem is there is no practical or affordable method available for accurately measuring the moisture% in small amounts of seed. The use of desiccant to dry seeds helps to ensure a low enough moisture level - especially in a warm and/or humid environment. In my area, forced air heating in winter drives the indoor humidity so low, that all I need to do is leave the seeds out until then. If I see a lightning storm when pulling off a sweater, I can safely assume that the seeds are dry enough. ;-) A good rule of thumb is the break test; if a seed breaks cleanly when bent, or shatters when struck with a hammer, it should be dry enough for frozen storage. If it bends, breaks incompletely, or just crushes when struck, it may need more drying. Regarding the removal of frozen seed... IMO the best method to ensure the safety of a large lot of frozen seed is to pre-package it in small small quantities. This could be small sealed plastic bags, within a larger sealed container (such as a freezer bag or mason jar). That way a single packet can be quickly removed for planting or exchanges - while still in the freezer - without thawing the whole container. I should also add that at this time of year, the same precautions that apply to properly warming frozen seed, also apply to seed received frozen in the mail. As tempting as it may be to eagerly tear open that package, try to wait until the package/envelope warms to room temperature.

aw, Ken... a voice from the other side of age-related brain damage... I've got a jug of engine coolant in the garage. It is open. When you use engine coolant, it is mixed 50-50 with water... but, of course, when you need it and open a new jug, the stuff in the jug is undiluted... and can't be diluted to the correct amount until that jug is half-empty. And, of course, this always happens when you are leaving for a trip or going to a funeral or getting married or something, so you pour some into the reservoir and then dump in some water, shooting for about 50-50. You also don't have an indelible pen (or any writing implement)in your pocket, so you promise yourself you will remember and head off to your great aunt's bat mitzvah... and promptly forget until the next time you need engine coolant. I've got four sprayers so I can use one for really bad kill-everything herbicides and one for Round-up and the other two for whatever... and you'd think I could keep straight which was which... and you'd think that I'd immediately mark them with an indelible (I first typed inedible - that too...)pen, but every year I have to go through the "now which was this again???" two-step. I think I have 8 shovels. Short of painting one with a black skull and crossbones, there is no way this old brain of mine is going to keep a specific "shovel of death" tucked away in the shed. Add to that that I have a co-Idiot gardener... I think we'd better concentrate on cleaning up!