The color yellow heralds spring for our northern gardening friends, who eagerly watch for the first signs of the season in the early blooming forsythia bush and the cheery crocuses that poke their heads from the chilly soil. Those favorites won't grow in our subtropical climate, but yellow flowers can still brighten your garden this spring and throughout the year. The yellow trumpet-shaped flowers of the allamanda burst open to mark the beginning of the warm season in our area. Allamanda (Allamanda cathartica) blooms profusely throughout the year, except for its winter break. One of the most popular yellow-flowering ornamental plants for Florida, allamanda is also one of the easiest to establish in a sunny or part-sun garden.
Meet the allamandas
A variety of woody, evergreen plants in the Allamanda genus can be grown as ground cover, for hedges and screens, as upright shrubs and as vines on fences and other structures. Some produce blooms all year. Others have more limited blooming periods. Specialty growers carry several hybrids in a variety of colors: cherry, white, peach, chocolate, cream and golden orange.
Allamanda is rated for use in USDA zones 9 through 11, although homeowners in northern and inland counties should be careful to provide protection on especially cold nights for this Brazilian native, which grows wild throughout the tropics. Super-hardy and fast-growing, Allamanda cathartica is considered an invasive species in Queensland, Australia.
In Florida, a native yellow allamanda vine (Urechites lutea) will climb over just about anything that gets in its way. Planted in sun or part shade, it blooms throughout the year and tolerates fairly horrid conditions, including salty air, drought, sandy soil and neglect (other than regular pruning to keep its growth in check).
Ornamental allamanda plants, on the other hand, are easier to tame but less forgiving of complete neglect. They don't like shade or frost. Experts recommend planting them in well-drained, moist soil rich in organic matter, but they'll do fine in just about all soils. Pests typically aren't a problem, and the plants are drought tolerant, although you should provide some water during extreme dry, hot periods.
Select plant with care
Because there are such different forms of allamanda, be careful when shopping at the garden center to make sure you get the plant you really want. Select only a plant with the complete botanical name, such as these.
• Allamanda cathartica, commonly called ''Yellow Bell,'' ''Golden Trumpet'' or ''Buttercup Flower,'' is grown as a full-size shrub or vine and produces yellow flowers in warm months. The variety ''Cherries Jubilee'' produces lavender-red flowers in the warm months and can be grown in a container or above-ground planter, as a ground cover, cascading down a wall or in a hanging basket.
•Allamanda neriifolia, also called ''Bush Allamanda,'' can grow up to 6 feet as a shrub and produces yellow blooms throughout the year. It does not climb structures like a vine. 'Compacta' is a dwarf variety.
• Allamanda violacea is commonly called ''Purple Allamanda'' and can be grown as a vine or climbing shrub. Year-round blooms are reddish-purple, fading to pink.
Allamanda's cousin — mandevilla — looks very similar with its trumpet-shaped flowers and deep green leaves, but it's not nearly as hardy, especially during hot, humid weather, says Dennis Dreier, general manager of the 70-acre wholesale Florida grower Altman Specialty Plants in Loxahatchee, which supplies Target stores with its flowering plants.
Allamanda produces its flowers on new growth. Time your pruning appropriately so you don't diminish flowering, particularly with plants that don't bloom all year long.
Except for the Allamanda neriifolia shrub, all other allamanda plants are poisonous to humans (not pets) and produce a toxic milky sap when cut. Wear protective clothing — gloves, long-sleeve shirt and long pants — when pruning or you may develop a burning, itchy rash and possibly blisters. I made the mistake of wearing a short-sleeve T-shirt while pruning Allamanda cathartica and ended up with drops of the white sap on my arms that required cold compresses for the intense burning, plus Benadryl to calm the itch.
Horticulturists claim the sap has antibacterial and anticancer properties, but I'd rather wash with antibacterial soap and eat my veggies.
Yvonne Swanson is a freelance writer in St. Petersburg and a master gardener for Pinellas County.