geranium, david phlox, stokeosia, hosta - Knowledgebase Question

kalamazoo, MI
Question by dfgquilter
August 11, 2008
Hi. ... several quick questions.
My little geranium was doing fine in hot sun. All of a sudden it stopped puttin up new shoots. What would cause this?

David phlox... Does it encourage new blooms to pick off all those tiny old ones?

Do Stokeosia need full sun and should they be mulched all yr. or just in winter?
Is there a hosta that will stay pretty in the hot sun ? Or, which is the best for sun? I have a few in sun and I should get the best kind for that.
Thanks so much for all your detailed help!

Answer from NGA
August 11, 2008


Geraniums will stop growing and blooming if the weather is too hot but will resume when they aren't so overheated. Just continue to give your geranium good care and it should recover.

In my experience, David Phlox only produces one flush of blooms each year. After blooming, cut off the spent flowers taking a few of the upper leaves with them to prevent disease. (Overcrowded plants can develop fungal diseases.)

Stokesia thrive in full sunshine and mulching will help slow water evaporation in the summer and help protect the roots during the winter months. I'd mulch them all year around.

Hostas are usually termed 'shade-tolerant' plants, meaning they will grow in shade or partial shade. But shade might not be their ideal growing condition. Some hostas need a period of full sun to look and perform their best.

It is not recommended that any Hosta be in full sun all the time, but many Hostas are more vigorous and display their most vibrant colors if given at least some sun exposure. Here's a quick rule of thumb:

Hostas with yellow leaves or fragrant flowers can stand more sun than Hostas with green, blue or white leaves. There are, of course, always exceptions and you may know of a Hosta that is basking and thriving in full sun, but that is not rule.

In general, yellow hostas need to be planted in a sunny location to keep their yellow color vibrant. Without at least a couple of hours of full sun, the yellow color will fade to green, or worse, look like a green leaf that is yellowing.

Similarly, fragrant hostas, those in the species H. plantaginea, need exposure to sun to develop their flowers. H. plantaginea is one of the most heat tolerant Hosta species.

Keep in mind, the heat experienced in a full sun location can vary from area to area and even during different times of the day. Full sun in the morning hours will not be as intense as full sun at noon. While yellow and fragrant hostas need some sun exposure, they do not like to bake or fry in the sun. So if your site is extremely hot or dry, you will need to keep any hostas sitting in full sun well watered.

The green, blue and white foliage hostas will grow in shade or partial shade ( no Hosta is going to thrive in deep shade). They all need some sunlight to photosynthesize. The shade tolerant varieties seem to do best in an exposure of morning sun and afternoon shade Too much sun exposure will result in burned leaves, starting from the edges inward. They will look brown and dry, like the leaves in the photo to the right.

Blue hostas require the most protection from the sun. This is because the blue color is actually a waxy coating on the leaves. The leaves themselves are a shade of green. The waxy coating gives them a blue tint. In full, hot sun, this waxy coating melts and exposes the green leaf underneath, changing the color of your plant from blue to green. It could also expose the leaves to burning. Spraying the leaves with a pesticide or fertilizer can also cause the waxy coating to melt.

Unfortunately, only trial and error can tell you which Hostas with white variegation can tolerate full sun without burning. The thicker the leaves, the more tolerant they will be of full sun. White variegated Hostas with thin leaves, like 'White Christmas', should be confined to partial shade to maintain their best appearance.
Another problem with white variegated hostas is that the leaves are white because they have minimal amounts of chlorophyll. In full sun, the chlorophyll levels can increase and cause the leaves to pick up a green cast and look less variegated. So only morning sun is recommended for white variegated hostas and the thinner the leaves, the less sun.

You can follow the rules and choose the recommend plants and still not have success. The only real gauge for how sun tolerant a plant is, is how it is performing. There are two clear signs that tell you your Hosta is getting too much sun:
Browning on the tips or outside edges of leaves; Dull color or faded spots on leaves.

If your Hosta plants aren?t doing as well as you would like, don?t be afraid to move them. Hostas are strong plants ad can withstand digging and replanting.

Hope this answers all your questions!

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