Starting a Fertilization Program
Before starting a turf fertilizer program, a soil test should be done to determine existing fertility and pH levels of the soil. The soil test will show the level of available phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). These major elements are essential to normal plant growth and should always be present in adequate amounts. Nitrogen (N) is usually not determined in a soil test because most soils are inherently low in nitrogen because it is readily leached through the soil profile. However, N is the most important nutrient for plant growth and therefore must be continually supplied in a turf fertilizer program.
The first step is to correct deficiencies of any element identified in the soil test results. Soil testing is available from commercial laboratories or the CTAHR Agriculture Diagnostic Service Center at UH-Manoa (beyond Oahu, contact the nearest CTAHR Cooperative Extension Service office). Fertilizer recommendations are given as a part of the soil test report.
Hawaii lawns are basically Warm-Season turfgrasses. Although there are some companies selling Cool-Season turfgrasses that have been specifically adapted for Hawaii's tropical climate-- they have not and these grasses will not survive the warm weather.
Many areas in Hawaii are exposed to salt spray, located over shallow water tables with high salt content, or irrigated with brackish water. Salt tolerance is therefore of great importance in these areas. Fortunately, there are several grasses that have a good degree of tolerance of salinity. If a shallow salt water table or poor-quality irrigation water is the problem, however, salinity may build up to levels that are higher than even the most tolerant turfgrasses can survive. Periodic leaching with fresh water is necessary to flush the salt from the surface soil in these areas.
Grasses well adapted for these conditions include Seashore Paspalum and St. Augustinegrass and to a lesser degree Zoysia Japonica.
Water restrictions are becoming more prevalent on the islands and some thought should be given to installing turfgrasses that have some drought tolerance. Those grasses include Buffalograss, Bermuda grasses, and Zoysiagrasses.
Hilograss (invasive weed)
Both popular grasses on the islands feature dense growth, spread by stolons and underground rhizomes. Although available in seed, the preferred method of planting is sod or plugs. Plugs can take up to 5 months for establishment depending on the season planted.
El Toro: 7 - 14 day for optimum growth and appearance at a height of 1/2"
Seashore Paspalum: 5 - 10 day for optimum growth and appearance at a height of 3/4"
NOTE: the extremely low mowing heights require a rotary mower
Both grasses have thatch, but Seashore Paspalum has a more rapid buildup of thatch and may require verticutting to control this thatch. Mowing this grass on the low end of mowing heights will help reduce thatch buildup to a certain degree.
Weed Control & Herbicides
El Toro: will tolerate many of the post-emergent herbicides commonly used for treating weeds
Seashore Paspalum: is very sensitive to post-emergent herbicdes