Hardy hibiscus zone 4

Tuesday, May 8, 2018 Perennials

Hardy Hibiscus for Northern Climates

l will never forget the first time I saw tropical hibiscus in the landscape. It was on a trip to Hawaii years ago where I saw huge beds of sunny yellow hibiscus shrubs clustered around an outdoor spa. It was a sight so beautiful that I remember it vividly to this day.

But sadly, living in Iowa at the time, I knew I could never duplicate that look in my home garden. Sure, I do grow tropical hibiscus in pots during the summer (they love Iowa’s hot, humid climate), but come fall, they fold up shop after the first frost blackens their foliage. (Note: you can save tropical hibiscus if you move them inside during the winter; see how.)

Then, one day, I was visiting a public garden in Chicago and stumbled across my first hardy hibiscus, Disco Belle Pink (in photo at left). It had huge, dinner-plate sized blooms with white and pink petals and a red eye. You couldn’t miss it even though it was planted in a huge mixed bed of other perennials. On top of that, they told me it was winter hardy even in Chicago! I don’t know where I’d been all my life, but clearly I was missing out on hardy hibiscus.

Since then, I’ve always included hardy hibiscus in my garden. All they need is full sun and hot weather. In fact, once the summer heats up you can almost watch these flower factories put out new growth. The plants do get pretty large, often becoming 4 feet tall and wide, so you need to give them plenty of elbow room in the garden. In photo below, for example, a hardy hibiscus is almost as large as a mature Limelight hydrangea.

Hardy hibiscus flowers are usually some variation of pink, red, or white with big, showy leaves that are either bright green or maroon. Some top picks include: Disco Belle Pink, Luna Rose, Mars Madness, Midnight Marvel, Peppermint Schnapps, Mocha Moon, Luna Pink Swirl, Luna Red, and Luna Blush.

In the North, hardy hibiscus dies back to the ground after the first freeze, but once warm weather returns in the spring they pop out of the ground like a Jack-in-a box. The plants are also resistant to insects, diseases, and hungry deer. It’s a must-have perennial for anyone who loves big, easy-care flowers.

Written by:
Doug Jimerson

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Dear Carol: My wife and I received a potted hibiscus tree that is 4 feet high and has bloomed continually all summer. My question is how I winterize this plant. We have an unheated garage and breeze way so temperatures are the same as the ambient air outdoors. We have a basement which may go down to 50 degrees F however no sunlight. — D.B., Hagaman.

Dear D.B.: Tropical hibiscus (Hibiscus rosa-sinensis) trees are great patio plants with showy flowers. They are hardy to USDA zone 9 or 10, minimum winter temperatures around freezing, as in south Florida, south Texas, and the Caribbean. The leaves will be damaged below 40 degrees or so.

You have a couple of choices if you bring the hibiscus indoors for the winter. The first is to move it indoors soon, before you turn the heat on. Keep it in a heated room in a brightly lit window. It will continue blooming for a while, and then will probably stop flowering and drop some leaves — maybe a lot of leaves. Don’t panic. This is a normal adaptation to the low light and dry air indoors. Keep the soil moist but not wet.

In the spring, when the days start getting longer, the plant will perk up and start showing new growth. Then you can cut it back to strong new outward-facing leaf buds and start fertilizing it lightly. After danger of frost, maybe in mid-May, you can move it outdoors again.

Tropical hibiscus are native to Asia but are grown as ornamentals in warm places all around the globe. The major species has single red flowers, but hybridizers have produced varieties in an array of colors, white, pinks, yellows and oranges. There are full double flowers as well.

Before you bring the plant inside, prune off any dead, damaged or diseased leaves or twigs. Inspect the plant carefully for any insects. Moving in and moving out are best done gradually to help the plant adjust. Move it in for a few hours, then out, then in for longer the following day. Do this for several days. Reverse the process in the spring.

The second method is to force the plant into a sort of semi-dormancy. Leave the plant outdoors until the temperatures are in the 40s at night. Then bring it into the cool dark basement. It is important to keep the plant cool. If the temperature warms up it will try to grow, and with no light it will die. Do not let the soil dry out completely; keep it barely moist so the roots don’t dry up and shrivel. This is a little iffier because tropical hibiscus do not normally have a dormant period. They grow all year around in their delightful natural habitat.

Two other possibilities. Let the plant freeze and buy a new one next year. They come up by the truckload from growers in Florida every spring. Or, load the hibiscus and yourself into the minivan and drive to a nice warm place for the winter. Keep the hibiscus on the balcony that overlooks the Gulf. It will enjoy the sea breezes. This option is sounding better and better to me, even though I enjoy winter.

Carol Bradford gardens in Syracuse. Send your questions and location to her in an email.

Help for Hibiscus Damaged by Cold

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Hibiscus Plant Care

Nothing feels more tragic than seeing your beautiful hibiscus garden get decimated by freeze damage. Tips of branches wilt and die, and the poor plants can end up looking like dead sticks covered with wilted leaves. What do you do?

Provide Warmth

If your plants are in pots, bring them inside. Warmth is the first and most important thing you can do for your plants. Ideally they should come into a bright room but not in direct sunlight. If you don’t have the ideal situation, bring them inside anyway. Warmth is more important than the type of sunlight! Use Houseplant Formula on your plants all through the winter and spring. It is our best possible formula for sick plants and will pull your hibiscus through the stress they have undergone more quickly than anything else you can use.

If your plants are in the ground, then provide some warmth for them outside. String Christmas lights around the plants, the old-fashioned incandescent type if you still have them. They provide more heat than the new LED lights. Be sure to use outdoor certified lights and outdoor extension cords. Then cover the plant and lights with freeze cloth, which you can buy inexpensively at any garden center or hardware store. You don’t need to remove the lights and freeze cloth. Just leave them on until all danger of frost is past.

Another way to provide warmth if your hibiscus are up against a house or fence is to tack plastic over them and fashion a mini greenhouse.

If a freeze catches you by surprise and your hibiscus are uncovered outside, turn sprinklers on them and leave them on all through the freezing night. Turn the water on high enough that it will sprinkle each whole hibiscus plant and really soak the whole plant. In the morning, your plants will be covered in ice ~ a scary sight for sure! But even ice helps insulate plants and keep them warmer in a freeze.

As long as there is danger of frost, resist the urge to prune your plants or remove the wilted leaves. Provide warmth and leave the plants alone for now.

Growth Enhancer and Fertilizer

Growth Enhancer can work wonders for cold-damaged plants! If you haven’t tried it yet, this is the time to try it. It is the first line of defense for any sick, damaged, or stressed plant, and if there is anything left to save in your plant, Growth Enhancer will save it. Don’t forget to keep using fertilizer too. Even if the top part of the plant is not growing, the roots need to keep growing underground, and the more vigorous root growth is, the more hormones your plant will churn out, and eventually the more top growth you will see. So continue to use both Growth Enhancer and fertilizer all through the winter months. Or if you prefer, you can simply use Houseplant Formula. It has both fertilizer and Growth Enhancer, along with many other nutrients, in the optimum doses for sick or stressed plants.

Now it’s Spring ~ Time to Clean Up and Prune

Be sure to have plenty of water-free hand cleaner with you because you will need to sterilize your pruners after every cut into damaged wood. Once you start pruning, you’ll also need to collect all dead, possibly diseased wood and put it in a plastic trash bag. You want to send all bad wood off to the dump in plastic bags rather than leave it lying around where it can spread disease back to your healthy hibiscus plants.

Checking for Live Wood

First check your plants for dead stems and branches. The test is simple enough. Working from the tip of each plant stem down toward the base, use a strong fingernail or a small knife to make a small scratch test (1/4-1/2 inch long). Scrape away a tiny bit of the brown outer bark of the stem that you are not sure about and look at the color underneath. A live branch will be bright green underneath the bark. If the branch is brown or light tan, it is dead. Some dead stems may be rotten, soft and squishy to the touch. There’s no need to do a scratch test on stems that are soft and squishy – they are clearly rotting and dead. Just keep working your way down the stem, doing scratch tests, until you find the point where scratching away the bark reveals bright, healthy, green plant tissue underneath. Plant tissue that is dull green with brown mixed in is not likely to live, so keep moving your way down the branch until you find a bright green patch. Now that we know where the live wood begins, it’s time to remove the dead wood.

Removing the Dead Wood – Two Strategies

Deeply Pruned Hibiscus Branch
Cut has clean, white wood inside bark.
New growth is sprouting below.

When cutting dead or dying wood from the plant, there are two strategies to choose between. The first is to find the highest spot of clean, live wood on a stem and then cut the stem 1/4 inch above the next visible node down from that spot. This will eliminate the ugly, dead wood and keep any disease from spreading downward. When you make the cut, the inner core of the stem should be clean and white, not streaked with dark stains. If it isn’t, then move further down the stem and keep cutting until you find good, clean, white wood. Keep in mind that the stem is likely to branch out from the node nearest the cut or from the 2-3 nodes just below the cut. Sometimes this is just fine, but other times that might make for a funny-looking plant with stems branching out near the top but not the bottom.

The second pruning strategy is to shape the plant while removing the dead wood. You start the same way, by finding the point where the wood is clean, green, and white. Instead of cutting just above the first clean, healthy node, the cut is made further down, just above a node that is pointing in the direction you would like a stem to grow. Be sure and cut 1/4 inch above the node, so that there is room for the new stem to sprout. If the cut is too high, the remaining wood above the node may rot. If the cut is too close to the node, you may remove the special plant cells that would have sprouted into the new branch. In this second pruning strategy, you remove more wood than is necessary to eliminate the dead wood. Some of what is removed will be white and clean but the idea is to force more stems to sprout lower down on the bush, to help it achieve a full and attractive appearance. You may cut away as much as 2/3 or even more of a branch in order to do this. Don’t be afraid to prune back many of the stems severely. The plant will re-grow with more branches than ever before and look fuller than ever before. More branches mean more flowers, too!

Some of the dead wood on a hibiscus bush will just be twigs. Remove the dead twigs as close to the branch they were growing from as possible without damaging that branch. Throw them in a trash bag in order to dispose of them.

Helping Your Hibiscus Come out of Dormancy

After cleaning up your hibiscus by removing all dead wood and pruning some branches for shape, what do you do? It will take several weeks, depending on weather, before your hibiscus will come out of dormancy and new growth will come back. During that time keep the hibiscus evenly moist if possible, and keep fertilizing and using Growth Enhancer.

To speed up the start of new growth, you can additionally spray your plants with Wake-Up Spray. Spray as often as daily until each new growing tip has its first set of real leaves, then cut down your spraying to once per week for 2-3 weeks more, then stop using Wake-Up Spray and let the Growth Enhancer and fertilizer do their work alone.

Hibiscus thrive on attention, and many of the cold-damaged plants from a cold winter will come roaring back to bloom again in the summer if they are given a little tender loving care as they recover from winter. As the temperature warms and summer approaches, increase your fertilizer and water, and add in Hibiscus Booster to increase growth and get your plants fully ready to start blooming. Stay vigilant for insect attack or use routine treatments on the plants as a preventive.

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