Oleanders are a bushy, woody flowering plant commonly used in landscapes for screening due to their tall growth habit. Growing tall oleanders in any environment requires fertilizer, water and proper pruning. Oleanders grow best in the tropical climates of the West Coast and southern states such as Texas and Florida. They thrive in both dry and humid conditions, and withstand wind without complaint, which makes them an excellent choice for screens and wind breaks. Normally oleanders bush up and out six to 12 feet in both height and width, and can grow up to 20 feet in height in tree form.
Fertilize oleander plants three times during the growing season to stimulate growth, usually in April, June and August. Apply one pound of nitrogen-based fertilizer for every 1,000 square feet throughout the area where oleander is planted.
Remove any suckers that develop on the lower parts of the plant stems or from the roots to keep these growths from siphoning off the plant's growing energy and the soil's nutrients. Use hand-held garden clippers or shears and cut the sucker at its base. Make the cut at a 45-degree angle to allow water to run off the cut rather than sit as it would on a flat cut, because sitting water breeds disease. It's best to cut the sucker completely off with one cut to avoid jagged cuts that might hold water.
Pinch the flower stemps with your fingers, or clip off with clippers, to encourage the upward growth and retard the lateral or bushing habit of the oleander. Pinch or clip off any wilting or dead oleander flowers at the first or second node of the flower's stem as soon as the spent flowers are apparent. Young oleander plants are easy to pinch with the fingers but as the plant matures and the stems harden it is necessary to switch to clippers to clip off the faded flowers.
Engage in a three-year course of "rejuvenation pruning" to maximize straight upward growth. In the first year after planting wait until flowering has finished and then prune off at the ground one-third of all the oldest stems. After the plant's second year in the ground, again wait until flowering is finished and then prune off at the ground half of the remaining two-thirds oldest stems. Thin out new laterally growing shoots. After the third year's blooms are gone, prune off at the ground the remaining oldest stems from year one, and thin new laterally growing shoots. Make all cuts at a 45-degree angle using clippers heavy enough for the size of the stems to be cut off. In the first year, single hand clippers are sufficient but as the oleander plants mature and the stems thicken and harden it is necessary to switch to heavier, two-handed hedge clippers.
Water deeply and thoroughly at least every two weeks and immediately after fertilizing. Oleanders do not require a tremendous amount of water, so extra water will encourage quick growth. Watering immediately after fertilizing allows the fertilizer to settle into the soil and reach the plant roots, giving the roots quick access to the fertilizer's nutrients.