Growing Concerns 245: Hibiscus buds falling and deer taste buds changing

I was given an indoor hibiscus. It flowered beautifully the first three months. After that buds would form and then fall off, unopened. It's going on two years and it has not bloomed again. The foliage is healthy -- dark, shiny leaves. I repotted it to a larger pot, set it outside in summer, even pruned it and still no blossoms! I fertilized my plants with every watering, and the humidity in my home during winter is 40%. Should I give up? - D.B. -

Tender hibiscus -- hybrids of Hibiscus rosa-sinensis -- are reliable flowering houseplants when given full sun, steady water, a well drained potting mix, and occasional fertilizer. They dislike change, however. Let the potting mix get too dry, the temperature change too rapidly, or the light levels fall off significantly for a few days and flower buds will abort.

Purdue University researchers looked at a common bud-drop situation -- plants in transit from greenhouses to retail location, which must spend several days in very low light. If in flower or bud, these plants drop 20% of their buds right away. Even if the plants were returned to optimal growing conditions right after the move, bud drop continued for five to ten days for a total bud loss of up to 93%.

That study concluded that even though bud drop was unavoidable after a significant change in growing conditions, good light levels before the change could reduce the loss. For hibiscus, that's just under 5,000 foot-candles. On a sunny, summer day there may be over 10,000 foot-candles of light outdoors. Indoors that same day, within three feet of a south facing window there may be only 1,000 to 3,000 foot-candles available.

 So think about changes your hibiscus has experienced and what you can do to reduce them. Do you move it periodically? A fixed location would be better. Does the plant ever dry down between waterings? That's stressful for a species adapted to constantly moist but well drained soil. Is it in a drafty spot, where temperature or humidity can fluctuate drastically? If some changes are unavoidable, increase light level with supplemental grow lights. Aim for at least twelve hours of light each day.

You may also want to revise your fertilizer regimen. Hibiscus likes a fertile soil, but to promote flower over leafy growth some growers swear by a formula that provides less nitrogen, more potassium, and includes micronutrients. Look at what you're using to see how it measures up -- nitrogen is the first number on the fertilizer label, potassium the third, and the presence of micronutrients is indicated by the words "with trace elements" or "with micronutrients".

 

I recently planted a new bed of purple-leaf sandcherry and black-eyed Susans. They became deer food in a matter of days. Is there anything that works to keep deer from destroying what's left? Are there any large flowering perennials that taste terrible so the deer will avoid them? - L.C. -

Every list of deer-proof plants we've seen has included at least one plant that we've known deer to eat, which is why we believe that each deer develops its own list. Add several deer in an area, each conducting personal taste tests, to the fact that even one deer-sized bite on a new perennial is a significant loss, and you'll understand why we don't bother with "deer proof" plants. We rely on fences such as the 90-inch tall, lightweight black mesh used at many botanical gardens. It's available for the public in stores and on the internet.

We've also heard great things about Tree Guard. Several gardeners in a position to use and compare products in a wide range of sites have told us that this repellent can significantly reduce deer browsing.  We have recently found this product sold online at www.conservationservicesinc.com/.