Each year, around mid-to-late summer, gardeners often notice something unusual about the hibiscus plants they purchased in early Spring.

The new hibiscus plants had been compact, with dense foliage, and covered with blooms. Then, after a few months, the plants become gangly, with more stem showing between the leaf nodes. And the original lavish display of blooms that looked so great at the nursery is greatly reduced.

What happened? Growth regulator hormone treatment. Many (probably most) commercial nursery-grown tropical hibiscus are treated with growth-regulator hormones to produce more compact plants and more blooms. These are the compact bloom-covered plants that are often sold in local garden centers.

The treatment slows the growth of stems, resulting in dense, compact plants. Because little energy is devoted to foliage growth, the treated nursery-grown hibiscus often have lots of blooms. The compact plants take up less room in winter greenhouses, have a wonderful thick bushy appearance, and are easier to sell.

With a little careful observation, it is fairly easy to spot plants that have been treated. Look at a well established plant in your garden (at least a year old), and notice that the leaf nodes on the stems are spaced anywhere from an inch to several inches apart. That is normal growth for most untreated plants.

Plants treated with growth regulators will have shorter stems, with leaf nodes tightly bunched together. As the treatment wears off, the space between nodes will gradually become longer as the plant reverts to a normal growth pattern.

Eventually, the treatment will wear off, and the hibiscus plants will revert to ganglier growth, with fewer blooms each day than the brand-new plants at the nursery. Unless treated again, the plant will exhibit its natural growth characteristics. This can be annoying, if one expected the plants to keep that compact and colorful “nursery fresh” look forever.

Hobby growers who like to graft hibiscus cuttings don’t like treated plants because grafts from such plants do not take well, if at all. Among serious collectors, the use of growth regulators is sometimes discussed with considerable dislike, even anger. Although most growers believe that a plant will eventually “grow-out” of the treatment, a few hybridizers claim that treated plants will never propagate as well as untreated specimens.

Of course, the original nursery growers of the plants may not be especially concerned about whether it is more difficult for people to make copies of plants. In fact, using hormone treatment to make new varieties harder to propagate might conceivably be used as a strategy to delay other grower’s “copying” efforts.

However, many specialty growers who sell tropical hibiscus at AHS hibiscus shows avoid treating their plants with growth regulators, knowing that advanced hobbyists & hybridizers will recognize, and may not buy, treated plants.

For the average grower or gardener, the effects of growth regulator hormones generally disappear within one year’s growing season, and the plants should then grow & bloom normally.

Because the adult non-treated plants will eventually spread out, give new plants room for new growth. Crowding encourages mildew, and facilitates spread of insects and disease between plants.

And BTW, growth regulators are not just used on tropical hibiscus. They are commonly used on a very large percentage of commercially grown flowering plants. Growth regulators can even be sprayed on hedges and grassy areas, to slow growth and reduce maintenance.

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