Weekly Home Horticulture Column
Archive - 2004, 2005, 2010, 2011, 2012, 2013
Q. The tree pollen from our trees is starting to fall. It is coating my car and our deck. Which trees is it coming from, and is there anything we can do?
A. It seems that we go directly from winter season to pollen season within just a few days.
I noticed on the news that the pollen index is considered very high for our area, and it probably will be for the next several weeks. If you have strong pollen allergies, you may already be hiding indoors and upping your allergy medication.
The pines and the oak trees are the main culprits in our urban forest that are producing all the pollen. These trees are wind-pollenated, and are known to produce copious amounts of pollen that can travel as far as three miles or more under the right conditions.
Pollen quantities will vary from one tree to the next, and from one season to the next, as well. Weather also has a big influence on the pollen count. Rain dampens the pollen and prevents it from flying in the air. Cold weather can slow pollen production and windy dry weather keeps the pollen flowing all over town.
A survey done by the University of Florida Forestry department found that trees most likely to produce a high amount of pollen in the Gainesville area are laurel and water oaks, loblolly and slash pines, as well as sweet gums and cherry laurels. If you are negatively impacted on days with high pollen counts, you can use a few strategies to stay more comfortable. Restrict your outdoor activities during days with high winds and low humidity. Shower after spending time outdoors to remove pollen from your hair and skin. Don't use trees that have a high pollen count in your landscape; trees like magnolia, tulip poplar and red maple would be better choices.
For more information about trees and pollen, visit the University of Florida IFAS extension website www.solutionsforyourlife.com.
Q. Last spring, we planted a few canes of sugarcane just to see if it would grow. It grew really well and we love it as an ornamental grass. But is has died back in the freezes. Will it come back, and should we prune the dead canes off?
A. Sugarcane grows really well in North Central Florida. It was often grown in the homesteads of early settlers for cane syrup and as a sweetener. Normally, the canes are harvested in late November to early December before a hard freeze kills them back. The roots are perennial, and soon new shoots will appear at the base of the old ones.
It is fine to prune the old canes off once the temperatures warm up. Fertilize the cane patch with a balanced fertilizer like 8-8-8 at least once during the growing season. Irrigate one to two times a week to provide about 1 inch of water.
You will grow an ornamental and edible grass that is beautiful to look at and sweet to eat. For more information about gardening, contact the Alachua County Master Gardener office at 352/955-2402.
Q. Is it too late to prune my crape myrtle tree? It is sort of a small tree, and I am not sure if I need to prune it or not.
A. In North Central Florida, we usually prune crape myrtle (if needed) in January or February, so you still have time to prune your tree. If the tree is small, you may not need to prune at all. Generally, we prune to maintain the size and shape as well as to increase flowering.
Crape myrtle produce flowers on the new growth, so a late-winter pruning for them is fine. When you prune this month, evaluate the shape of the tree: Do you want a multi-trunk tree or a single-trunk tree? Since your tree is small, you can easily correct any problems with the shape or the growth habit of the tree. If you want a multi-trunked specimen, select the three or four strongest trunks and prune the smaller side suckers down to the ground. This will provide more vigor to the primary trunks.
Do not over-prune the top of the tree or commit "crape murder." Everybody has seen this practice where overzealous pruners cut them way back.
This destroys the beautiful cascading form that the crape myrtle tree is known for. Removing more than one-third of the plant at any given pruning is stressful for the tree. Instead, give a gentle pruning by only pruning back the branch to a point that is about as wide as your thumb, or a 1-inch diameter. This encourages healthy growth and more blooms for the late spring.
For more information about crape myrtles and pruning them, visit the University of Florida/IFAS Extension website at www.solutionsforyourlife.com.
Q. I know it is time to treat the trouble spots in my St. Augustine lawn for crabgrass. While I was out shopping for a weed killer, I noticed a product that was made of cinnamon bark that said it would kill crabgrass. Do you think it will work?
A. February is the month to apply a pre-emergence weed killer for crabgrass. Crabgrass is an annual weed that doesn't start sprouting until the summer. So, if you had a crabgrass problem last year, treat with a pre-emergent herbicide in February to prevent the germination of the seeds.
Quick reviews of the cinnamon-bark product lead me to believe it is used on green and growing crabgrass, and doesn't have any pre-emergent effect on the seeds. The product information states that with a couple applications, it will get rid of the crabgrass.
An extension agent colleague in South Florida tested the product last year and found that the cinnamon-bark herbicide only burned the top of the crabgrass, and the plant re-sprouted from the roots. I really like the idea of a natural approach for this recurring summer weed, so maybe the formula can be improved.
In the meantime, treat your crabgrass trouble spots with an herbicide that contains pendamethalin (Halts crabgrass killer or Pendulum) to keep the crab at bay.
Give the UF/IFAS Alachua County Master Gardeners a call to help with weed issues at 352/955-2402.
Q. I have been overrun with air potato vines for many years. They grow on the back side of my property and in a spot that is next to a natural area. This past fall, I noticed lots and lots of holes in the leaves, and the vines seemed weaker. This must have been the work of the air potato beetle, right? I am worried that now that the vines have died down for the winter, this bug will come after my landscape plants. Should I be concerned about it?
A. This is the time of year that the invasive air potato vines die down, and it is the best time to pick up and destroy the bulbils or the "air potatoes." The city of Gainesville will host the Great Air Potato Round-Up in many of our local parks and natural areas this month. During the roundup volunteers pick up thousands of pounds of the potatoes to prevent the further spread of this invasive exotic vine. This year, there may be fewer potatoes collected because of the newly released air potato beetle (Lilioceris cheni).
Air potato vine (Dioscorea bulbifera) was an ornamental plant that was introduced to Florida in 1905. Since then, it has escaped from cultivation and grows unchecked in natural areas as well as Gainesville backyards. The vines can reach heights of 60 feet, and it will cover and smother the trees and shrubs it grows on. The vines are spread by an inedible bulbil, or air potato.
In Florida, nothing eats the leaves of the vine or the potato, so the vines spread aggressively — until now. Scientists have discovered a small beetle that feeds only on air potato. It was found in Asia where the vine is native, too. After extensive testing by the USDA/ARS, and the Florida Department of Agriculture, these beetles were found to only feed on air potato. The insect will not complete its life cycle on any other host plant. They feed almost entirely on the leaves of air potato vine, and sometimes on the bulbils. The beetle larva, as well as the adults, feed on the newly developing leaves, and this really reduces the plant growth and its ability to spread. Extensive damage usually is noticed on a stand of air potato vines within three months of release of the beetles.
The beetles do not die out in the winter, nor do they look for other things to eat. The adult beetles will go into a hibernation of sorts. The beetles will hide out under leaf litter or mulch. In the spring, the overwintering adults will emerge, and the females will start laying eggs. The young beetles will keep eating the air potato vines.
The beetles will not be released to the public for a couple of years yet, but they will be available at some point. For more information about the air potato beetle, visit the University of Florida IFAS Extension website at www.solutionsforyourlife.com.
Q. Several of my plants, like hibiscus, ginger and pentas, were burned back during the freeze. What should I do now? Should I prune them back or pull them up?
A. The cold temperatures of January can burn back some of our favorite plants in North Central Florida.
We recommend covering these plants with frost cloths or fabric that extends all the way to the ground. If it is going to be windy as well as cold, you should weight the clothes down so they do not blow off. Tropical and subtropical plants such as hibiscus and pentas should be covered when temperatures drop below 32 degrees. Plants like citrus and cold-weather vegetable crops (broccoli and collards) can stand temperatures slightly lower without protection. But, if it is going to be a "hard freeze" (below 28 degrees for more than five hours), you should protect your citrus and veggies, too.
The roots and lower portions of hibiscus, pentas and ginger will more than likely survive freezing temperatures, so pulling them up should not be necessary. The freeze damage should not be pruned back until you see new growth emerging later in the spring. If you prune the plants back now, it could stimulate new growth that might be further damaged by the cold. If it is possible to postpone clipping the plant back, try to hold off until at least March. If new green leaves start to grow from the stems, cover them with frost cloth to prevent further damage.
For more information about cold protection on plants, visit the University of Florida IFAS Extension website at www.solutionsforyourlife.com, or call the Alachua County Master Gardener Volunteer at 352-955-2402.
Q. I heard that Arbor Day is this month, but I know for a fact that Arbor Day is on April 25.
A. You are correct on both accounts. Florida's Arbor Day is always the third Friday of January. National Arbor Day is in April.
January is a good time to plant trees. You can celebrate by planting a tree in your yard or community. Consider strong trees like the live oak, bald cypress, winged elm or cabbage palm. Also flowering trees like crape myrtle, magnolia and dogwood can be planted now.
Gainesville is a designated Tree City USA. To keep this designation, the city must have an active tree board, a tree-care ordinance and community forestry program, and have an Arbor Day observance event. This year marks the 30th anniversary of Tree City USA for Gainesville. The Arbor Day celebration will take place 11:30 a.m.-1:30 p.m. Jan. 16 at The Depot Park. There will be speakers, music and a shade tree give-away.
For more information about the event, contact Ella Brooks at 393-8181, or Earline Luhrman at 393-8188.
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Air Potato Beetle
Cold Damaged Plant