Zinnia leaves brown/yellow

5 years ago

last modified: 5 years ago

Hi everyone, this is my first time with enough sun to grow zinnias and I have an "urban garden" in a city in NJ, zone 6B-7A (depending on the source). No plants had grown there for years except shrubby cinquefoil, and a community landscape crew mulched it before I planted and otherwise pretty much leave it alone for me. So hopefully soil shouldn't harbor too much disease. I started these from seed indoors from a color mixed pack and they'd been doing great! I had some aphids at first which I usually killed by squishing them, but the plants got nice and big anyway and I haven't seen an aphid in forever. But for 1.5-2 weeks I've noticed progressive crispy brown leaves on this one plant (and yes, the powdery mildew on its neighbor). Anyone know? I googled pictures of the common pathogens that affect zinnias but it doesn't quite match anything I'd seen. We had 2 hot, fairly humid, but almost rainless weeks and I watered the veggies a lot, but very rarely watered the zinnias which seemed to thrive anyway. Could it be an underwatering problem? There are hot & sweet peppers growing behind them and over a foot before the curb. Just this one looks affected out of 9 plants, but the top looks alright. I appreciate anybody's thoughts or experiences!

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Comments (4)

windberry zone5a BCCanada
5 years ago
Not enough water IMO. Under watered plants always start browning at the bottom.
Leah S thanked windberry zone5a BCCanada
ken_adrian Adrian MI cold Z5
5 years ago
look on the back of the affected leaves ... for mites or other sucking critters ...

to my eye... when a leaf goes all white brown like that.. something has sucked all the juices out of them ... then track it up ... and see if its an ongoing issue ... or something that has already ebbed ...

the mulch does look dry.. take a tablespoon.. and dig a 3 inch hole near the plant.. and discover moisture at root depth ... and then water accordingly to fix that issue.. if any ...

it never fails to amaze me.. how problems can find plants that are stressed ... so... fixing the bug.. will not fix the original issue.. so we have to make sure to get the plant happy ....

it never hurts to tell us where you are.. big city name ... it just helps us understand the situation better ...

as to the mildew.. how do you water?? ... never wet the leaves in the evening.. unless you are sure they can dry before night... when mildew prospers ... and dont rely on lawn irrigation for your plants.. now that they have roots deeper than grass roots ...

ken
Leah S thanked ken_adrian Adrian MI cold Z5
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gardengal48 (PNW Z8/9)
5 years ago
Agree with windberry - it is a water issue. Nothing to do with pests or diseases.

Believe it or not, better watering practices can also slow or prevent the development of powdery mildew as well. PM tends to thrive when weather is warm, soil is dry and nighttime humidity high. A deep soaking at the root zone will eliminate one of the contributing factors. PM spores cannot survive in water either so spraying/watering the plants early in the day can help reduce the spread as well.
Leah S thanked gardengal48 (PNW Z8/9)
Leah S
Original Author
5 years ago
Thank you everyone! No clues on the back of the leaves. I water by hand using watering cans (with many refills) because this is one of the only sections of my neighborhood that is not part of the sprinkler system. I focus on the bases and try not to hit the leaves and have to loosen up the soil/mulch pretty regularly at the bases because beneath the top layer of mulch is a compact layer from years past that water will just run right off. My timing is erratic because my work schedule is. The soil quality is also very erratic - this part seemed pretty normal, other sections were full of clay. And some sections had old bricks and metal grates beneath them - urban gardening made me feel like an archaeologist. I amended areas around the holes on planting day with Black Kow but may have not done a big enough area. Funny enough the zinnias never looked droopy when all the other thirsty plants did. I will bump up the watering - fortunately my rain barrel got its first fill shortly after I posted that. Thanks for all your help!