Expert: C.L. Fornari - 9/26/2005

Question
I don't know if petunias are an annual or not.  I'll plant a number of petunia plants and they seem to do quite well.  Although, I always removed the dead blooms, I just read that I need to prune them back.  My problem is that something seems to make my plants wither and die one by one, as if the predator is moving from one plant to the next.  I haven't been able to visibly see any pests.  What pests like to attack petunias and do this?  How can I solve the problem?

Also, I have another question that I don't know if you can help me with.  I have a problem with spiders spinning webs over my plants and flowers, whether they're out in the open or on my screened in porch.  I don't like to use chemicals.  Do you know of any natural remedy, perhaps something I could spray on them and their webs to encourage them to leave the premises?  Many thanks for your help.

Answer
Gail,
Petunias are annuals, but not to worry in any case: people ask me all sorts of plant questions through AllExperts.  Different types (varieties) of petunias last for differing amounts of time.  I have had some petunias that last well into October (the Wave series) and some that give out in mid-August.  In general, in order for petunias to last a long time they need deadheading if they are the regular type  and not Wave or Superpetunias that don't make seeds.  You need to snip the stem that is just below the wilted flower, because the idea is to remove the developing seeds, not just the wilted flower.  Every two weeks you should also snip 2 or 3 branches back by half.  THis keeps the plants bushy and full, and encourages the new growth that has the most flowers.  You should also either use a time-release fertilizer when you plant or fertilize them with a liquid feed every two or three weeks.

In regard to your plants wilting, it is more likely disease not insects.  Plants that wither and die are usually either too wet or too dry - both can cause plants to show those symptoms.  If the petunias are kept too wet they get root rot that is caused by a fungus, and it is possible to move from plant to plant (insects usually attack all plants at about the same time, rather then moving down a line)  The other thing that can cause petunias to wither and die is mildew - a fungal disease that turns leaves grey and then they die.  This fungus comes from the soil and the weather conditions (humid but little hard rainfall) cause the fungus to thrive.  Some years a petunia might get mildew and some not.  Other things that can cause this are if the plants are getting hit with hot water as it first comes out of the hose (plants get cooked) or if they get a leaf fungus from being frequently hit with water every day....water plants deeply less often instead of everyday, and let the water cool before watering the plants.

Unfortunately there is nothing that will keep spiders off the screen porch except a frequent appearance of the broom.

all the best,
C.L. Fornari
www.gardenlady.com