Hot Weather Hibiscus

It's hot!

Early June has brought Houston temperatures in the mid nineties pretty consistently, several degrees warmer than the average for this early part of the month. And there isn't much that exotic hibiscus flowers like about temperatures in the mid nineties.

The plants, though, will grow vigorously through these temperatures if you can keep them adequately watered and keep some nitrogen and iron in the pots. Both leach out easily when you apply as much water as these temperatures warrant.

Using soluble fertilizers like Space City Hibiscus Food will provide the frequent snacks that exotic Hibiscus need during this season. Weekly is not too often, and add some magnesium sulfate once a month. If the veins are darker than the bodies of the leaves, some copperas is a cheap and easy way to replace the low iron.

Is there anything that can be done about the beautiful blooms that are missing or short-lived during such weather? Yes, there is.

Most obviously, those Hibiscus plants in pot should be moved now to shadier spots. Morning sun and afternoon shade is a precious commodity, as is the filtered light of pine trees or Drake Elms. You'll have a little less growth but more and better flowers. Very little direct sun is really necessary for summer flowers of Hibiscus rosa-sinensis here.

While the exposed foliage of most of these varieties can tolerate full sun, the roots are much less adaptable. Consider how unnatural it is to confine any plant in a pot for life. The lack of a normal root run means water and nutrients are drawn from a much, much smaller volume of soil. Add to that the elevation of summer temperatures found in container grown Hibiscus, and you have a formula for trouble.

In the natural state the shade of a bigger plant and leaf litter and all sorts of organic matter generally insulate the roots from the sun, and feeder roots can grow more deeply in response to summer heat. None of those benefits are present in our black plastic pots.

Yes, white pots would be better, reflecting radiant heat as they do, but they become a focal point in the landscape if exposed. A better solution is to insulate your roots. Placing your Hibiscus in a plastic pot of choice, it is inexpensive and simple to slip that growing pot inside a second pot which is identical or slightly larger, creating a dead air space between the two pots. Dead air is a good thermal insulator, and you can lower the temperatures in your Hibiscus plants' root zones dramatically with this method. We find that this translates to more blooms, less water loss, less wilting, and generally happier plants, especially in full sun.

You can insulate even more effectively by adding some inert, granular matter to the void between pots, perhaps calcined clay (cat litter), but just the dead air space can make a big difference, especially for container plants receiving afternoon sun.

Other growers insulate roots by nestling the plastic pots into a raised bed filled with pine bark or filled with healthy annuals or perennials which can shade the pots. Bachelors' Buttons, Lantana, summer petunias, and many other options can be used effectively. Avoid hosts to spider mites and consult a nurseryman for advice in this regard.

Some hobbyists dig holes in flower beds and nestle the pots directly into soil for the hot summer. It is harder to judge when to water with this method, but of course it will be less often than for a pot sitting on top of the ground. Moving the pot to a protected area for the winter is a guaranteed struggle, because roots will escape the pot drain holes and anchor the pot into the surrounding soil. Attempting to life out such a pot becomes a lumbar nightmare unless you cut the roots with a sharpshooter or other tool in advance of trying to lift it.

Several years ago pots were marketed that had copper sulfate painted on the inside, because that compound repels roots and can promote more thorough saturation of the soil with feeder roots in such a pot. One can find on the internet simple formulas for painting such pots yourself, if you are suitably adventurous. Pots of this sort reduce the problems associated with sinking a pot into the soil of a flower bed.

In recent days we have been religious about cooling off the hibiscus in the late afternoon by hosing them down with cool water from the garden hose. As that bathwater evaporates, it carries away lots of BTUs of heat energy, leaving the plants cooler and happier. More buds stay on and flower size and quality in sunny sites improves. It is a perfect opportunity to provide an extra measure of water for those rootbound containers which really want to wilt at 95°F. In addition, a daily hosing washes off dust and tree pollen and disrupts the life cycle of insect and mite pests, and lets you solve little problems before they become widespread challenges. We get a little of the water into all pots, but wet the foliage very thoroughly.

If you wish to make best use of your Hibiscus blooms in this hot weather, consider picking the flowers before the sun and heat fade them. Picking buds before you go to work will yield nice flowers before noon, and they will last well. Refrigerating picked buds the morning they were due to open, can delay their opening for a few days such that your fine flowers can open and decorate an evening or afternoon event the day you remove them from refrigeration. Slip the picked buds into a zip lock bag with a damp paper towel as moisture source to prevent dessication.

This month pay special attention to the varieties that continue to bloom and to those that do not. Our summers are so protracted that a non-performer in the heat is hard to justify space for. Ask your hibiscus friends for names of good bloomers in the summer heat, and consider replacing your hibernating varieties with better performers. Many doubles are notorious for doing a disappearing act in summertime.

Generally speaking, yellows, light pinks, and white blooms can tolerate full sun the best, and heat-absorbing dark colors need the most shade.

Finally, remember that your health is more important than your hobby, and protect your skin from sunburn and potential cancers with sleeves and hats and sun screen. Drink lots of water, avoid alcohol, and consider eating a banana per day to keep your potassium high enough to avoid the cramps associated with hot weather perspiration outdoors. You may feel that you need sports drinks that replace potassium quickly when heat stress is worst, but natural sources are wiser choices most of the time.

Be well, do good work, and keep in touch . .

Barry

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