How long do Zinnia seeds remain viable in the soil or mulch?

HighlanderNorthJuly 15, 2014

This is the 3rd year that I have been growing these Burpee zinnias from seed that, although advertised to grow to 30-36", usually grow to at least 5-6 feet tall every year I have grown them, regardless of how much sun they receive! They grow flowers of at least 4" diameter or a little larger, and the packs seem to include flowers of at least 7 different colors and shades of similar colors.

They got powdery mildew last year for the 1st time, in August after about 2 months of blooming, but although their leaves became whitish gray, they still continued blooming. That brings up question 1: How to prevent powdery mildew on zinnias? They are fairly tightly packed because they get larger than the packages claim, and wider as well. They also grow LOTS of large lateral branches that spread out all over! They have large, deciduous hibiscus in front of them, but no large plants on the other 3 sides.

Anyway, I mixed in 2 of these large Burpee cactus flowered zinnias with the other variety, so there are about 8-9 plants in front of the house, and they have been blooming for nearly a month now, and are already between 4-5 feet tall!

Back on topic: Last year's crop dropped countless seeds onto the bed they are planted in, and the bed was re-mulched this year in early May right after planting the zinnia seeds there. But I dont yet see but 1 or 2 plants that apparently have grown from the seeds that fell last year, and no other seedlings anywhere! I do have zillions of these white-flowered Daturas that are popping up all over the place, from seeds that dropped from their flowers last year, but no zinnias.... So, if they arent 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?

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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.

(not associated with any product or vendor mentioned or linked)

    Bookmark   July 15, 2014 at 4:15AM
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docmom_gw Zone 5 MI(5)

I suspect that any zinnia seed that falls to the ground and gets rained on will germinate immediately, but then is killed by cold temperatures in fall/winter. Therefore, in cool climates there are very few seeds left by spring. Also, mulching prevents any light from reaching the seeds, so they probably mold from the moisture and dark. I always save seeds from my zinnias and start them in small pots in early spring. Once they are large enough to not be lost, I plant them and spread fine mulch around them to minimize weeds and preserve moisture.


    Bookmark   July 15, 2014 at 10:25AM
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To zen man: I forgot to mention that I had applied some Bayer 3 in one rose and flower, and I applied it to the roots by mixing with water and pouring it on the soil, as opposed to any spray application of pesticides because I also am essentially aiding the local praying mantis population by monitoring their egg sacks and relocating them if they are on branches that are pruned off in the fall. I don't want to kill them or effect the bee population. I really didn't want Ty use imidicloprid, but I also had some insect issues as well. I want to only apply natural remedies from now on..

I also apply the miracle grow or the Vigoro brand. The Bayer 3 in one was applied 2 weeks ago.

    Bookmark   July 15, 2014 at 2:22PM
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ken_adrian Adrian MI cold Z5

I have been growing these Burpee zinnias from seed that, although advertised to grow to 30-36", usually grow to at least 5-6 feet tall

==>>> you are not growing what you started with.. as to cultivar status ...

you are growing genetically mixed seed ...

meaning... you are growing the grandchildren.. they dont look like grandma and pa ...

and that is why they are now taller ... and any other trait which is different ...

Z seed doesnt winter over for me in z5 MI ... go figure...


    Bookmark   July 15, 2014 at 4:45PM
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To Ken_adrian: I am not growing the next generation from last year, or the previous year's plants. Each year I buy a new seed pack, or like in the case of this year, I just used the 2nd half of the seed pack I bought last season. Only 2 of the 9 or so zinnias growing now are even possibly from last year's crop. But the thing is, there are 2 local stray cats that live in 2 sheltered cat boxes right there on the property near the zinnias. They were apparently dropped off a few years ago by who knows who, and we have essentially taken care of them by having them spayed/neutered so they dont continue having more and more kittens, and they are fed twice a day. But they are 100% outdoor cats that will NOT come indoors, because they dont want to, and because there are already 2 cats here who live indoors and one of them was badly injured by 1 of the strays.

Anyway, the point is, these 2 strays use the mulch bed as their personal litter box, and we cant seem to stop that from happening. So, even though I created a roped off area for the zinnia seeds to grow in that front bed, the cats still got in there and repeatedly raked up the mulch and some of the soil underneath of it in order to cover their poops! In the process, some of the zinnia seeds and even little seedlings had been dug up by the cats when they used it as a litter box. So I had to replant some new seeds 2-3 times this spring. I even sprayed this hot pepper based animal deterrent spray to keep them out of the seed bed, but it wears off every time it rained.

As a result, I guess its possible that the 2 separate zinnias that are coming up a few feet outside of the main zinnia site are actually just seeds I had planted from Burpee seed packs earlier this spring, but had been 'relocated' by the cats....Or they could be from last years seed drop, but the more I think about it, the more I doubt that because they are the only ones that came up, even though countless seeds were dropped last fall.....

    Bookmark   July 15, 2014 at 5:16PM
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