Expert: C.L. Fornari - 6/26/2010

Question
Hi,

In April I finally got around to purchasing a windowbox for my front window and some cheap-and-cheerful trailing blue Lobelia plants from a local store.  I planted them in good, composted soil and feed and water regularly.  

It is now the end of June and, whilst they have tripled in size (if not more) there aren't as many flowers as I expected; just lots of green shoots, with a small sprinkling of blue flowers and a few shoots waiting to bud.

I was hoping that it would be a "waterfall" of blue flowers.  Do you know whether it would just be a case of biding my time or whether I'm over-watering them perhaps or they are just not very "good" plants?  They get some direct sunlight during the day (when it's sunny!)

I'm in the UK, and the weather has been surprisingly good lately, with high temperatures.  I water them generously every evening.

Thanks for any help you can give in putting my mind at rest.

Answer
Gavin,
Trailing Lobelia is kind of a heartbreak plant, unless you live in Alaska. First it breaks your heart because the blue color is so beautiful - then because once it gets hot, and if it's in too much sun or shade, it stops blooming.  If the temperatures are above 23c then these plants stop blooming. If they get less than 3 to 4 hours of dead on sun, they stop blooming. And if they get all day sun and it's hot they stop blooming.

If your plants are getting the 3 to 4 hours and it hasn't been above 23 C in general, than perhaps it's a matter of fertilization - water the plants well and then give them a liquid fertilizer, either one with numbers that are fairly equal (10-10-10 etc) or one that has a slightly higher first number - most annuals are Nitrogen hogs.

I hope this helps,
C.L.