Ageratum and Coleus: shade or sun?

(Question)

I just read one of your articles entitled “Annuals for Shade” in which you list Ageratum and Coleus as examples of shade-happy plants.  Other online sources that I have read list these two plants as loving full-sun gardens.
Please can you clarify?

(Answer)

The vast majority of plants are not exacting in their cultural demands and can grow within a range of conditions.  As our guide Annuals for Shade states, “different annuals will tolerate different degrees of shade”.

Ageratum may need full sun for best flowering, but will tolerate and flower in light shade, where many other flowering plants refuse to bloom.  Therefore, if you have a lightly shaded spot in your garden, where more popular annuals like pelargonium and petunia will sulk, ageratum will give a much more satisfying show.  But if your goal is to have as many blooms as possible on the ageratum, then give it full sun (i.e. 6 hours of direct sunlight or more).  However, not all full sun conditions are created equal.  An ageratum in a cooler climate like Toronto will happily bask in full sun, but will suffer under full sun in a hot climate like Texas, where it should be provided part shade.  Therefore, to state that ageratum loves a full-sun garden is, at best, incomplete.

On the other hand, the statement that coleus loves full sun is again, not quite accurate.  Coleus, grown primarily for its vivid multi-coloured foliage, should not be sited in full sun, since too much sunlight can cause sun-scald with the leaves being bleached out, developing crispy edges or thin brown spots.  The more sun the plant gets, the thirstier it will be, so watering is vital.  Coleus is best grown in part sun to part shade, ideally getting morning sun and then protection with shade from noon through the hottest hours of the afternoon.  Dappled shade is ideal, not deep shade.

I hope this clears up the confusion.