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Annuals/petunia problem


QUESTION: I simply cannot get my petunias to bloom 3 weeks after bringing them home. They are in large pots which I keep well-drained, and I have been deadheading them when I think of it. I do have a real problem with slugs on my front porch; I can see the slimy trails! When I bought them about a month ago they were gorgeous and lush, but little by little they have gone to nothing. I probably need to deadhead more but it really doesn't seem to help. Maybe its the slugs? They are supposed to be such an easy plant, but for me they're not, even in previous summers. Would appreciate your help. I live in zone 7B, NC.

ANSWER: Petunias are the perfect summer plant, provided you have the light to grow them, and you deadhead.  (Slugs, yes, can ruin everything.  But a strip of copper tape (easy to find on will block them from raiding the refrigerator at night.)

Deadheading Petunias takes dedication, which you clearly have.  What a shame then that your hard and diligent work has not paid off.  I wonder therefore -- please let me know -- if these plants are not getting enough sun.

Petunias have a basic need for ENORMOUS amounts of sunlight.  This short speech from Purdue's Consumer Horticulture website will spell out the basics of current science:

Note they point out that plants are able to make use of only "1%" of the sunlight that reaches their leaves. Even I did not know that. I suspect that what they are trying to say is that plants use only the BLUE and a small amount of RED light; the rest is fluff.

Researchers love to work on Petunias. They have important relatives (Potatoes, Tomatoes, Flowering Tobacco, Eggplant) and are easy to work with.  Research on Petunias has found that their leaves are loaded with Chlorophyll-a, C55H72O5N4Mg, which is very blue-green, and   Chlorophyll-b, C55H70O6N4Mg, which is yellow green. You have to feed these Chlorophylls photons.  Let there be light, if you are growing Petunias.

There is also something else to consider, next time you pick these up at the store.  As you know, "photoperiod" is an important factor for some plants and not others.  This has nothing to do with the brightness of light, whether you grow your plants in sun or shade.  Photoperiod is the LENGTH of the day.  Wave Petunias, the current state of the art for this species, will bloom regardless, but the bloom MUCH quicke rif you cater to their need for 14-hour days.  This is how the grower got them to flower before you bought them.  Like spoiled children, the Petunias your purchased were indulged and pampered and then they were force-fed to the point where they would look exquisite for a brief time, just long enough to get you to put them in the shopping cart and take them home.

The effects continued for weeks.  But the luxurious lifestyle your Petunias led is over.  They are in the real world now, and the fact that you go to the trouble to dead head them makes this a good deal for them.  Because most people do not have the knowledge, and even fewer have the time to put up with this.  (I do too but I love the fragrance.)

So you can figure there is going to be a transition period.  They need to rest.  Think of it as literally too much of a good thing that you Petunias got before you brought them home.  They must adjust.  They cannot flower while they do this.  Their resources are depleted.  The well is dry.  You cannot get blood out of that stone.


So let's recap.  You need to give your Petunias light -- as in, if you spend 15 minutes in that light and you get a burn, the Petunias will be SO HAPPY to hang out with you in that kind of sunlight.

Continue to deadhead.

Tape away the slugs.  Do not fertilize.  Soil should be poor.  Most important, move them if you can to a location where the sun shines so intensely, you may as well be at the beach.
Keep me posted and you are welcome to post a followup.


---------- FOLLOW-UP ----------

QUESTION: My petunias get full sun, so I think I'm going to cut my losses and go with something else in the future. Thanks again for your fine info!

Your guess about slugs -- based on the slimy evidence they leave behind -- makes them a likely suspect.  But you haven't said anything about these plants losing leaves.  This is easy to check:  Go out there just before bedtime with a flashlight and check.  You don't even have to look under the leaves.  Simply stroke the plants in the dark with one hand and see if there's anything cold and wet.  Slugs are voracious vegetarians when it comes to Petunias, which have small leaves compared with other garden plants.  Where a slug will chew a hole in an impatiens leaf, it will eat the entire leaf of a Petunia.

Beer dishes are touted as effective ways to control slugs, but I fail to see how this can make any real dent in a population that is likely in the thousands.  Yes, the thousands.  You want to decimate the snails and even getting 25 a night -- a high number for a single dish -- is simply not going to work.  Copper tape is a better choice.

Slugs will likely go after anything you plant there, so consider slug control seriously.

Now, suppose it's not slugs that are the problem?  Petunias are highly susceptible to Beetles and Aphids.  Potato Flea Beetles -- Epitrix cucumeris -- are mini-bugs that look like black specks.  They hop around and eat round holes in the underside of Petunia leaves.  They jump like fleas when disturbed. However, whether or not you are dealing with Potato Flea Beetles depends on the weather in your neck of the woods.  In these parts, Flea Beetles don't hatch until mid-June and it's another 10 days before they start doing damage.  You did not mention your location.  If you are dealing with this problem in the same approximate latitude as New York City, look for the little black dots.  Here's a photo of a leaf with the telltale little hole and the bug itself:

You have not mentioned fertilizing, nor did you describe the soil these are growing in.  It is very important NOT to give vitamins and minerals to Petunias.  They respond by growing leaves, roots and stems.

I'm really curious about this.  Keep me posted,



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Decisions, decisions... If you can't make up your mind which Annuals to grow, you're not alone. Problem with your new flowering Annuals flats? I`ve been there, done that. Petunias, Sweet Alyssum, Larkspur, Marine Blue Lobelia -- they all grow here at my house on Garden Street on Long Island, N.Y.. Cutting and Cottage Gardens, Sun and Shade Gardens, White Gardens and Night Gardens, I`ve done them all. Annuals are the perfect summer flower, bursting with color June through fall's first frost. I can`t speak on Cactus or tender Tropical Plants -- they don`t grow outside in my Zone 7. I`m no Farmer, so I cannot guide you on Fruits and Vegetables. But whether it`s an Annual you want to start from seed, mail-order or pick up at your local garden center, I can help you grow amazing blooms this Summer. Yes, together, we can turn your neighbors green with envy.


I have a lifetime of gardening behind me here on the North Shore of Long Island. While I have degrees in related fields, there's nothing like hands-on work to build real knowledge. I stay on top of current science -- there's a boom in research, and Kingdom Plantae is filled with surprises. By the way, I really do live on Garden Street.

Gannett newspapers, The New York Times, and hundreds of others - but not on Annuals.

B.A., botany; graduate credits in European Intellectual History and Political Science; minor coursework in related fields, docent training at our local botanical gardens (required for volunteers). I'm currently working on an advanced biochemistry degree.

Awards and Honors
I could tell you, but then you'd know who I am.

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