by Sheila Dunning | Dec 23, 2014
A frozen perennial plant. Photo credit: Taylor Vandiver UF/IFAS Extension.
When you look out at your landscape nobody has to tell you that winter temperatures in Northwest Florida Afterwards, the temperatures warm up and you feel compelled to do something about it. You just need to “turn your back and slam the door”. “Conceal, don’t feel; don’t let them know”. Cold injury can affect the entire plant or just certain plant or parts such as fruits, flowers, buds, leaves, trunks, stems, or roots. Many plant parts can adapt to tolerate cold. Root systems in the landscape are seldom ‘frozen’ in Florida. “The cold never bothered” them “anyway”. While dead, unsightly leaves may be removed as soon as they turn brown after a freeze, the remaining dry looking stems serve as food storage and should be allowed to remain. If they are removed before the weather is warm enough for the plant to resume growth, the root system may not be enough to support the plant and it will die. So, “let it go, let it go, let it go”. “The perfect” landscape “is gone”. “The past is in the past”. “It’s funny how some distance makes everything seem so small”.Tropical plants and summer annuals do not adapt or harden to withstand temperatures below freezing, and many suffer injury at temperatures below 50°F (10°C). Subtropical plants can harden or acclimate (become accustomed to a new climate) to withstand freezing temperatures, and properly conditioned temperate plants can withstand temperatures substantially below freezing.
Recently planted, unestablished plants may be more susceptible to cold injury. One type of winter injury is plant desiccation or drying out. This is characterized by marginal or leaf tip burn in mild cases and totally brown leaves in severe cases. Desiccation occurs when dry winds and solar radiation result in the loss of more water from the leaves than can be absorbed and/or transported by a cold root system. Plant water needs should be checked after a freeze. Plants may have lost substantial moisture during a windy freeze. Plants will transpire (lose water vapor) on a sunny day after a freeze. Cold injured wood can be identified by lightly scraping the bark with your fingernail and examining the color of the cambium layer (food conducting tissue) just underneath. Green tissue indicates the plant is still alive at that point; black or brown coloration indicates dead or injured tissue. 
After a particularly harsh cold event, some plants may be very slow to recover, so some patience is required. “It will rise” with “the break of spring”. Branch tips may be damaged while older wood is free of injury. Delay pruning until new growth appears next spring to ensure that live wood is not removed. In the meantime, take Elsa’s advice and “let it go, let it go, let it go”. You may be “too relieved to grieve”. I hope I haven’t infringed on any copyrights by letting you know “It’s okay to put off the yard work in the name of plant physiology”.
Enjoy the holiday season!
For more information please see:
Treating Cold Damaged Plants
by Sheila Dunning | Dec 2, 2014
Camellias have been a part of the landscape in the Southeastern United States for over 200 years. They are native to Asia and were introduced near Charleston, South Carolina in 1786. The common name camellia refers to varieties and hybrids of Camellia japonica and to lesser known varieties of C. sasanqua and C. reticulata. The growing conditions in Northwest Florida are well suited for many camellia varieties. Camellias can serve several functions in the landscape including foundation plantings, screens, accent plants, background groupings and hedges. Maximum benefit can be achieved by mass plantings or groupings. Single plants should be focal point in beds rather than randomly placed throughout the lawn. Camellias flower in the fall and winter when their display of colorful blooms is most appreciated. During the remainder of the year their evergreen foliage, interesting shapes and textures, and relatively slow growth make camellias excellent landscape plants. Some camellia growers enjoy competing in flower shows and manipulate the flower buds to achieve larger and earlier flowers. This involves removing competing flower buds and applying gibberellic acid (a plant hormone). Individual cultivars can be selected for size and form ranging from small and irregular to large and upright. Texture and foliage color also differ among the various species and multiple varieties. Mid-season flowering varieties that bloom from November through January are best suited for Florida conditions.
Warm fall temperatures may prevent early varieties from flowering properly. Late-blooming selections may attempt to send out new leaves before the end of the flowering period which results in “bullnoses”. Bullnosing is characterized by poor quality flowers which do not open fully and may even drop while still tight buds. Extended dry periods while in the bud stage can make the condition more likely. While flowering, camellias need 1 inch of water applied each week. Camellias perform best in partially shaded locations which are enhanced by good drainage and air movement. Fertile, acidic soils high in organic matter are preferred. The soil must be well-drained because camellias will not grow in wet areas. Do not plant them in areas with a high water table and/or hard-pan. This will result in a shallow root system which is more susceptible to injury during dry periods. Camellias should be installed where cold air can move in and out freely, but the area should be protected from strong northwest winds. Plantings under established trees or in areas that has structures to block the wind are usually injured less by cold temperatures. These conditions enable the plants to gradually thaw or warm in the morning before being exposed to direct sunlight. Dense shade may result in sparse foliage and poor flowering. Camellias exposed to full sun may appear yellow-green, but may yield more flowers. Either situation is stressful to the plants and can lead to pest problems. Tea scale is the most common insect on camellias. Scales generally feed on the underside of leaves and may not be noticed until large populations have developed. Symptoms include very small elongated white and/or brown raised “flakes” on the underside of leaves that turn yellowish in color. Tea scale can be controlled with horticultural oil, sprayed after flowering finishes but while temperatures are sill cool, in late winter.
by Sheila Dunning | Nov 4, 2014
Since 2005, multiple varieties of Diascia have added to the U.S. fall market of winter flowering plants. Its delicate flowers are far from ordinary though. In the early part of the last century most British gardening encyclopedias listed just one diascia – Diascia barberae – derived from seed collected by Col. J. H. Bowker and sent by Mrs. Barber to Kew Gardens, England, in 1870. Annual and perennial diascias had, of course, already been discovered and classified by several botanists visiting South Africa much earlier. The dainty, little annual, Diascia barberae, is not a very showy flower, but one which will appeal to the true flower lover. The flowers are rosy pink with yellow-green spots in the throat. The flowers are lipped, being related to the Snapdragons, but have two spurs on the lower lips, and are sometimes called twinspur. It was not until John Kelly was given a plant called Diascia cordata by Edrom Nurseries in 1971 that anything notable happened to diascias again. He took pollen from his Diascia cordata and applied it to one flower of Diascia barberae. Of the nine seeds he obtained, just one was worthy of attention. He named it Diascia ‘Ruby Field’ (not for the color of the flowers, but for a lady who devoted her live to the long-term care of deprived children). Despite the popularity of this new, hardy hybrid, little more happened with diascias for yet another decade. The boom in the diascia trade began only recently. Today’s diascia offers larger flowers, larger plants with a more open growth habit and colors ranging from scarlet through salmon and coral into pink. They bloom throughout the cooler weather and may behave as a perennial in warmer sites. But, the uniqueness of their flower structure and ecological role are as fascinating as the flower is beautiful. 
The common name of twinspur refers to the two downwardly pointing spurs found on the back of the flower. The spurs contain an oil which is collected in the South Africa wild by Rediviva bees. The female bees have unusually long, hairy forelegs that are used to collect the oil to feed her larvae. However, the Greek origin of the Diascia name doesn’t refer to the spurs, but rather the two sacs found in the upper part of the corolla. The flower petals help the bees to 
orient themselves to the oil glands of the spurs. While North Florida isn’t home to the Rediviva bee, we can grow Diascia and it is a wonderful opportunity to show the unique connection insects and plants can have. Look for other specialized flower structures and you will find other animals that fit them perfectly, even within the species found in the Panhandle.
by Sheila Dunning | Sep 23, 2014
Photo Credit: Candy Butler, Floridata.com
Looking to add something to brighten your landscape this autumn? Firespike (Odontonema strictum) is a prolific fall bloomer with red tubular flowers that are very popular with hummingbirds and butterflies. Its glossy dark green leaves make an attractive large plant that will grow quite well in moderate shade to full sunlight. In frost-free areas firespike grows as an evergreen semi-woody shrub, spreading by underground sprouts and enlarging to form a thicket. In zones 8 and 9 it usually dies back to the ground in winter and resprouts in spring, producing strikingly beautiful 9-12 inch panicles of crimson flowers beginning at the end of summer and lasting into the winter each year. Firespike is native to open, semi-forested areas of Central America. It has escaped cultivation and become established in disturbed hammocks throughout peninsular Florida, but hasn’t presented an invasive plant problem. Here in the Panhandle, firespike will remain a tender perennial for most locations. It can be grown on a wide range of moderately fertile, sandy soils and is quite drought tolerant. Firespike may be best utilized in the landscape as a mass planting. Plants can be spaced about 2 feet apart to fill in the area quickly. It is one of only a few flowering plants that give good, red color in a partially shaded site. The lovely flowers make firespike an excellent candidate for the cutting garden and is a “must-have” for southern butterfly and hummingbird gardens. Additional plants can be propagated from firespike by division or cuttings. However, white-tailed deer love firespike too, and will eat the leaves, so be prepared to fence it off from “Bambi” if they are a problem in your neighborhood.
by Sheila Dunning | Aug 19, 2014
Pine bark beetles are frequent pests of stressed pines in the southern United States. The five most common southern pine bark beetle species include three in the genus Ips. Ips beetles usually colonize only those trees that are already stressed, declining, or fallen due to environmental factors. Infestations may occur in response to drought, root injury, disease, lightning strikes or other stresses including flooding.
Ips calligraphus usually attacks the lower portions of stumps, trunks and large limbs greater than 4” in diameter. Early signs of attack include the accumulation of reddish-brown boring dust on the bark, nearby cobwebs or understory foliage. Ips calligraphus can complete their life cycles within 25 days during the summer and can produce eight generations per year in Florida. Newly-emerged adults can fly as far as four miles in their first dispersal to find a new host tree, whichever one is the most stressed.
Most trees are not well adapted to saturated soil conditions. With record rainfall this past April, the ground became inundated with water. When the root environment is dramatically changed by excess moisture, especially during the growing season, a tree’s entire physiology is altered, which may result in the death of the tree.
Water saturated soil reduces the supply of oxygen to tree roots, raises the pH of the soil, and changes the rate of decomposition of organic material; all of which weakens the tree, making it more susceptible to indirect damage from insects and diseases.When the ground becomes completely saturated, a tree’s metabolic processes begin to change very quickly. Photosynthesis is shut down within five hours; the tree is in starvation mode, living on stored starches and unable to make more food. Water moves into and occupies all available pore spaces that once held oxygen. Any remaining oxygen is utilized within three hours. The lack of oxygen prevents the normal decomposition of organic matter which leads to the production and accumulation of toxic gases such as carbon dioxide, methane, hydrogen sulfide and nitrogen oxide. Additionally, within seven days there is a noticeable root growth loss. Roots only develop when soil oxygen levels are at 5% -15%. Over time, the decaying roots are attacked by pathogens. The loss of root mass from decay and fungal attack leaves the tree prone to drought damage. After only two weeks of saturated soil conditions the root crown area can have so many problems that decline and even death are imminent.
When a tree experiences these anaerobic soil conditions it will exhibit symptoms of leaf loss with minimal to no new leaf formation. This usually appears two to eight weeks after the soil dries out again. Many trees will not survive, especially the more juvenile and mature trees. However, well established trees may still decline several years later, if they experience additional stresses such as drought or root disturbance from construction.
There is little that can be done to combat the damage caused by soil saturation. However, it is important to enable the tree to conserve its food supply by resisting pruning and to avoid fertilizing until the following growth season. Removal of mulch will aid in the availability of soil oxygen. Basically, it is a “wait and see” process. While water is essential to the survival of trees, it can also be a detriment when it is excessive, especially for drought tolerant pine species such as Sand Pine, which is prevalent throughout the coastal areas.
For urban and residential landscape trees, preventative strategies to avoid tree stress and therefore reduce the chances of infestation include the following:
1) avoiding compaction of, physical damage to, or pavement over the root zones of pines,
2) providing adequate spacing (15-20ft) between trees,
3) minimizing competing vegetation beneath pines,
4) maintaining proper soil nutrient and pH status and
5) limiting irrigation to established pine areas.
When infested trees are removed, care should be taken to avoid injury to surrounding pines, which could attract the more harmful pine bark beetle species Dendroctonus frontalis, the Southern Pine Bark beetle.
There is no effective way to save an individual tree once it has been successfully colonized by Ips beetles. In some cases, the application of an approved insecticide that coats the entire tree trunk may be warranted to protect high-value landscape trees prior to infestation. UF/IFAS Extension can assist with recommendations.
