Question
what to do? I have these in flower boxes, cannot seem to keep them alive.  I water often, i water infrequently..i replace these little flowers OFTEN.  How can I keep them alive?
thanx!!

Answer
We are growing Vinca major here, yes?

This Vinca (Catharanthus roseus) ranks as one of the Top 10 Most Popular Bedding Plants in the country. It comes in different colors and sizes; it can take hot, dry areas, tolerates all kinds of soil and won't succumb to neglect.

I know, I know, those French-style plantings with vinca draped gracefully down the side of the boxes in front of the windows - charming, oui?

Note s'il vous plait that this delicate little darling of windowboxes can be a royal pain in the neck.

This is a "hardy" plant to the extent that it can take zero degrees Fahrenheit.  But if you are thinking that "hardy" means "flexible", it will wither and croak as fast as you can say Eiffel Tower.

Sounds already like maybe you've been there, done that.

Here we go: Vinca 101.

There are 3 kinds of Vinca: Creeping, Dwarf and Border.

Creeping Vinca is the one to grow in hanging baskets or trailing out of planters. It needs full sun to do best. This includes "Magic Carpet" Vinca.

Dwarf Vinca is a dense, small flowered plant that grows to a maximum of 1 ft tall. This group includes the "Little" and "Cooler" series. Dwarf Vinca is used for hanging baskets but some designers think it looks better in small planters because it does not drape like creeping Vinca.

Border Vinca has the biggest flowers (2 inches) and grows the fastest and tallest (14-20 in).  "Tropicana", "Heat Wave", "Pacifica" and "Victory" are Border Vincas. These are commonly seen in commercial landscapings with large planters.

Make sure you buy healthy Vinca plants which have not been stressed.  Reason: the fickle, slow-growing roots are the most vulnerable part of this plant; left to dry out to the point of wilting, Vinca roots rarely recover to pre-stress levels.  Buying your Vinca plants from a discounter or simply a retailer whose staff might be too casual about letting flats dry out -- or overwatering them -- may be the only reason your plants have not done well so far. Once Vinca roots are damaged, all bets are out the window.

Vinca is happiest in hot, dry areas with full sun, poor soil with a low pH (acidic) and great drainage, and hair-drying heat. Like petunias and zinnias, it finds rich soil an alien environment.  Unlike petunias and zinnies, it will not grow lots of leaves in response -- it will simply succumb.

Nor will Vinca tolerate humidity or moisture -- leaves and flowers must be kept dry and spells of London fog or drizzle are unbearable.

There's more.

Vinca is picky about its fertilizer.  It shows disdain for high Ammonia-based Nitrogen or Phosphorous fertilizers.  If you use a Nitrate fertilizers, make sure it is low in Phosphorus.

Let's look at your flower boxes.

Are they well drained?  If your Vincas had faces, would they look at those flower boxes and smile from ear to ear?  Would they clap?  Would they LOVE your flower boxes?

Because it is possible that those roots are giving those Vincas a Sequoia-size headache.

Shallow is bad.  No drainage is bad.  No drainage holes are fatal.

Remember, the roots are the achilles heel of this plant. If you treat them like the roots of any other potted plant, the whole Vinca will give you the silent treatment or worse just check out.  On the other hand, if you keep the plant dry, if you water just right, if you give it just the right sun and air, it will trail gaily in all directions and put on a lively, carefree show that is nothing less than... Magnifique!

Thanks for asking.

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Summer afternoon - summer afternoon; to me those have always been the two most beautiful words in the English language.
?Henry James