A WORD OR TWO ABOUT GARDENING

Some sunny garden color

In a previous article som e m onths ago the subject of color in the landscape w as introduced. On that occasion the focus w as on blue flowering , and it w as evident that, although there are a few spectacular plants to choose from , the range is lim ited. With yellow flow ering plants, the subject of this colum n, the choice becom es overw helm ing. From pale lem on, through bright golden to the glow of a m ore orangey yellow , these vibrant sunny colors and m ore can be found in the plants described below. Bright colors such as yellow suggest im m ediacy, shortening distances in the landscape – they are useful in foundation plants or those used to fram e an entrance. Avoid overuse in a sm all yard, especially around the perim eter w here creating a sense of depth w ould be m ore appropriate (blue/violet flow ering plants). In a larger yard, a bright yellow border w ould be ideal for an open expanse of turfgrass. In addition to and vines, space could also perm it the placem ent of one or m ore yellow flow ering . There are few m ore glorious sites than a leafless yellow tabebuia in full bloom against a bright blue, early spring sky. Even if the show is rather short lived, it is spectacular. Little w onder that a yellow tabebuia (Tabebuia chrysantha, el araguaney) is the national of Venezuela. This particular yellow tabebuia is uncom m on in M iam i-Dade, the silver trum pet tree (T. aurea syn. T. caraiba) being by far the m ost frequently planted species. The com m on nam e refers to the silvery scales present on the leaf surface. This tree has a reputation, locally at least, for being w eak rooted and prone to w indstorm dam age. To reduce the risk of trees toppling, avoid planting specim ens that are root bound, and sites that have poorly draining soil. In addition, w ell aw ay from roads and buildings, and prune out storm dam aged lim bs to avoid subsequent disease problem s. A third yellow tabebuia that is som etim es seen locally is the golden trum pet tree, T. chrysotricha, w hich is a som ew hat larger (30 – 40’), m ore open tree. It can be distinguished from T. aurea by having less corky bark and the presence of reddish brow n tom entum (fuzz) on the stem s, undersides of leaves and capsules (the pod-like fruit). Yellow tabebuias lose all or m ost of their leaves before bloom ing in spring, and should be kept dry during w inter. Flow ering w ill also be im proved by avoiding high nitrogen fertilizers and w aiting until after bloom ing to feed the tree. Closely related to the tabebuias w ith sim ilar yellow , trum pet shaped flow ers is the yellow elder (Tecom a stans). This 10-12’ fast grow ing, som ew hat straggly tree/ requires pruning to keep it tidy, and has pinnate leaves as opposed to the digitate leaves of the tabebuias. The plant is som etim es grow n as an inform al screen, but its m ain attribute is the im pressive late sum m er/fall show of brilliant yellow , sw eetly scented flow ers. Tecom a castanifolia is very sim ilar, but has a m ore erect grow th habit and is easier to train as a sm all tree. Both plants readily self- seed, and can be w eedy – rem ove volunteers as they appear. Another m em ber of the Bignoniaceae, M arkham ia lutea (m gam bo, from central Africa) is a 30 – 40’ drought tolerant, deciduous tree developing an attractive trim , pointed crow n. It has yellow , bell-shaped flow ers w ith a reddish brow n throat (the cultivar ‘Pierrii’ has a m aroon striped throat), occurring in term inal panicles from spring into sum m er. The tree is not particular as to soil, providing it is free draining. The bean fam ily () contains m any yellow flow ering trees/shrubs, of w hich the cassias are best know n. Taxonom ically they are separated into tw o separate genera: Cassia spp. are larger, often deciduous trees, and Senna spp. sm aller, usually evergreen trees and shrubs. The golden show er tree, Cassia fistula, w hich flow ers in late spring/early sum m er, can be used to continue the yellow them e of the yellow tabebuias. Golden show er trees grow to about 30 – 40’ and are considered the tropical equivalent of the , w ith fragrant, very show y, pendant racem es of pale yellow flow ers. The leaves are pinnate, com prising 6 – 16 unusually large leaflets (8x 3¼ ”), the fruit a long, thin, cylindrical brow n pod. The tree can be prone to root rots, so avoid poorly draining sites and root dam age. Leaf spot diseases are som etim es a source of concern, how ever this is a tem porary problem as the tree is briefly deciduous before flow ering in early sum m er, after w hich new leaves em erge. The Kenyan show er tree, Cassia afrofistula, w hich is sm aller, tends to form m ultiple trunks, w ith flow ers in upright panicles. The tree is evergreen, drought tolerant and has an extended bloom period from sum m er into fall. The Senna spp. trees flow er late sum m er to fall, though som e such as the desert cassia (S. polyphylla) can also flower on and off throughout the year. This particular tree, native to the Virgin Islands and Puerto Rico, is sm all (8 – 10’), relatively slow grow ing, w ith delicate foliage and sm all clusters of yellow flow ers. It is an excellent choice for a sunny, dry spot in a sm all yard, and like other sennas, tends to becom e shrubby. Prune out the num erous shoots that develop from the root crow n to retain a tree-like grow th habit. The glaucous cassia (Senna surattensis), w hich form s a m ore substantial sm all tree (12 – 15’), is com m only seen in south Florida and frequently used to landscape local m alls. This tree, like several other sennas, is also a favorite w ith caterpillars (sulphurs), and on occasion feeding can dam age flow ering shoots (not a problem for butterfly aficionados!). Com pared to the desert cassia, the glaucous cassia has a denser canopy, often becom ing top heavy, rendering it liable to toppling in w ind storm s. How ever, it is otherw ise a reliable tree, and rem ains attractive year round. Other sm aller sennas are used as shrubs: for instance the candlestick cassia (Senna alata), a 4- 10’ shrub w ith erect spikes of yellow flow ers, and Baham a senna (S. m exicana var. chapm anii), a native, large shrub w ith flow ers in flat panicles. Both of these sennas flow er during the w arm er m onths of the year. Staying w ith trees in the Fabaceae, m ention should be m ade regarding the confusion surrounding the yellow poinciana. There is indeed a yellow flow ered variety of the royal poinciana (Delonix regia) available as D. regia var. flavida. As the tree often does not com e true from seed it needs to be grafted, a fact that contributes to these being expensive and of lim ited availability. There is also another species, Delonix elata, w hich has m uch paler alm ost w hite flow ers and is even rarer in local landscapes. To add to the confusion the nam e yellow poinciana is also applied to various Peltophorum spp. (35 – 45’ evergreen trees), in particular P. dubium . The flow ers are a vibrant yellow , differing from D. regia var. flavida in having crum pled clustered in a m ore upright spike. Peltophorum pterocarpum is better know n as the copperpod, the nam e referring to the copper red seed pods. All of these trees are fast grow ing w ith shallow surface roots, w eak w ood and develop poor structure unless correctly pruned. They are show y trees, but best planted w ell aw ay from sidew alks and buildings. Another group of show y, yellow flow ering shrubs/trees from the Fabaceae are also som etim es referred to as poincianas. These are the caesalpinias, of w hich the dw arf poinciana (Caesalpinia pulcherrim a) is probably the best know n, though locally less in evidence than 20 -30 years ago. This is an open, som ew hat prickly, shrubby plant, w hich bloom s on and off throughout the year producing flow ers w ith crim son petals edged w ith yellow . A selection w ith all yellow flowers, C. pulcherrim a var. flava, is also available. Caesalpinias are suitable for open sunny areas, able to survive poor soil and drought – a good choice for xeroscapes. The divi-divi (C. coriaria - the signature tree of Aruba) survives exposed beachfront locations w here, in response to the prevailing w ind, it develops its’ characteristic lopsided, contorted, flat topped appearance. In m ore sheltered situations the divi-divi can grow to m ore than 20’ w ith very attractive, delicate foliage and sw eet sm elling cream y yellow flow ers. Nom inally evergreen, the tree drops leaves as tem peratures approach 40ºF. M ore substantial than the divi-divi, the bridalveil tree or granadillo (C. punctata syn. C. granadillo) is outstanding as both a m edium size (30 -35’) shade and flow ering tree. In addition to the golden yellow , sum m er/fall flow ers, the tree develops a full open canopy w ith crim ped, com pound leaves and an attractively m ottled grey/brow n trunk w ith peeling bark. This tree is a good alternative to one of the Peltophorum spp. above. While the flow ers are not quite as show y, it develops a m ore pleasing form and is m uch less prone to storm dam age. Before leaving the bean fam ily, tw o other trees should be m entioned. The first, Jerusalem thorn (Parkinsonia aculeata) is an airy, sm all, deciduous tree w ith w ispy green stem s, num erous spines and com pound leaves com posed of m any tiny leaflets. It is covered with clusters of yellow flow ers, spring - sum m er. Once com m only seen, it has largely fallen out of favor locally, being m ore at hom e in an arid clim ate. The tree is prone to root rots and die-back in south Florida. M ore suited to local conditions, the Jam aican rain-tree ( ebenus), is, slender, spiny, but larger (20 -25’) w ith, ragged peeling bark. The long drooping branches are covered w ith sm all sessile leaves - show y orangey yellow flow ers appear during the w arm er m onths in response to heavy rainfall. Vera w ood, Bulnesia arborea, is increasingly popular as a choice, m edium size, yellow flowering tree. It is in the sam e fam ily as lignum vitae and like that latter tree produces very hard, dense w ood. The paired flowers are golden yellow to alm ost orange, w ith spoon-shaped petals, the com pound leaves com prising 9 pairs of obliquely set, curved leaflets. This, but m ore particularly the opposite arrangem ent of the leaves and the fruit (a 5-w inged capsule), distinguish vera w ood from legum inous trees such as cassias, w ith w hich it is som etim es confused. Grow th is initially m oderate, but slow s as the tree reaches its locally m atures height of 30 -35’. Avoid planting root bound specim ens w hich establish poorly and are m ore liable to fall over in a w ind storm . Established trees are drought tolerant, low m aintenance tree and quite w ind resistant if correctly pruned during early developm ent. The yellow Geiger tree ( lutea) is even m ore tolerant of drought, but difficult to train as a tree unless started from seed. The flow ers are yellow , sim ilar to the m ore fam iliar orange Geiger, but the leaves sm aller, w ith crenulate m argins. A plus factor: unlike the orange Geiger, C. lutea leaves are not disfigured by Geiger tree beetles. One final tree, the golden rain-tree, Koelreuteria elegans (Sapindaceae), is at present m ore conspicuous for the coppery pink, inflated seed capsules. Prior to this in late sum m er it is covered w ith pyram idal spikes of yellow flow ers. This 30 -40’ tree adapts w ell to poor soil providing it is free draining – root rots can be a problem . It has w eak w ood (prune correctly to m inim ize potential storm dam age), and is on a w atch list as possibly invasive (produces m any seedling volunteers). There are several vines are w orth m entioning. The chalice vines (Solandra spp.) are vigorous w oody vines (20 – 30’) that require a sturdy trellis or pergola. The flow ers are fragrant, large and cup shaped w ith a flared lip, pale yellow (S. longiflora) or golden yellow (S. m axim a), and are in evidence sum m er into fall. Where pruning is necessary, cut back heavily once flow ering ceases. The yellow allam anda (Allam anda carthartica) is less vigorous, ideal for covering a fence w ith bright yellow trum pet shaped flowers. A num ber of large flow ering cultivars are available of w hich the ‘Hendersonii’ series are m ost often seen. Grow in full sun using enriched soil, watering during hot, dry, w eather, w ith m ajor pruning in early spring (caution, sap can cause derm atitis). On M iam i-Dade’s calcareous soil, foliar applications of m anganese m ay be needed to correct leaf yellow ing. If a m ore shrub like plant is desired prune m ore frequently, but it is easier to use the related bush (dw arf) allam anda, A. schottii. For a m ore slender w oody vine, Brazilian golden vine (Stigm aphyllon ciliatum ) provides glow ing yellow , butterfly-like flow ers through sum m er into fall. Grow in full sun w ith som e afternoon shade. Thryallis (Galphim ia gracilis) is a sm all (3-5’) shrub that bloom s for m uch of the year w ith clusters of sm all yellow flow ers. This is a useful source of yellow in the landscape for areas that are shaded for part of the day – stem s are brittle so choose a site protected from strong w inds. A num ber of yellow flow ering plants in the are available, and w ill stand som e light shade. Less shrub and m ore herbaceous perennial, all of these plants have a tendency to becom e leggy, and benefit from pruning after flow ering. Best know n is yellow candles (som etim es offered as golden shrim p plant), , w hich produces cone-like spikes of w hite flow ers, w ith show y golden yellow bracts. The true shrim p plant, brandegeana, is available as cv. ‘Yellow Queen’ w ith bright yellow bracts. Not as fam iliar is the giant yellow shrim p plant (often listed as Barleria m icans, but probably B.oenotheroides), w hich appreciates som e partial afternoon shade from hot sum m er sun. Related to the barlerias, Ruttya fruticosa - jam m y m outh) is infrequently seen in local landscapes but ‘Scholesei’, a yellow flow ered cultivar, is som etim es available. The is a spike, w ith unusual flowers having the petals fused into a protruding upper lip and a curved low er lip w ith a brow n blister like blotch in the center. Eventually becom ing a 10 -12’ spraw ling shrub, it can be cut low as a ground cover, or pruned into a sm all bush, and w ill take dappled shade. Where there is m ore shade (bright light) try the yellow flow ered cultivar of crossandra, Crossandra infundibuliform is cv. ‘Lutea’ – provide evenly m oist soil. Finally tw o sm all shrubs, the first of w hich, sage rose (Turnera ulm ifolia), is quite com m on in local landscapes. It produces a profusion of short-lived, 2”, bright yellow flowers throughout the w arm er m onths of the year. The leaves are glossy and have a strong resinous odor w hen bruised. Apart from pruning to prevent it from becom ing straggly, this plant requires little attention. The one caveat: a definite tendency to becom e w eedy in the landscape. With w inter approaching the final plant, Reinwardtia indica (yellow flax), w ill provide brilliant yellow flow ers Decem ber to M arch. This is a soft stem m ed, low shrub rather undistinguished until it bursts into flow er early in early w inter. Provide full sun and a m oist but free draining soil - it can be difficult to m aintain through a south Florida sum m er but it is w ell w orth the effort.

John M cLaughlin October 19, 2004