Design or redesign a landscape

Estimate the water needs of landscape plants

Photo: Close-up of flowers

Determining a factor for landscape plants other than turfgrass, part 2: Observation-based approach

Assigning a species factor, KS

The species factor (KS) in the equation for calculating KL accounts for the fact that different species have different needs for water. Based on field observations, horticulturists have evaluated the water needed by various species of landscape plants.

Observation-based estimates adapted from two of the most comprehensive lists currently available are included in Table 3, which covers trees, Table 4, covering palms, Table 5, for shrubs and vines, Table 6, for ground covers, Table 7, for perennials, and Table 8, for agave, cacti, succulents, and yucca. Use these tables to assign an appropriate species factor (KS).

Note that these estimates are for established species. Also note that, if the Ks recommended in one of the tables for a species is less than 0.1, the species needs no irrigation once established, except perhaps during drought years.


You want to assign a KS to the bougainvillea in your Pomona, California, landscape.

  • You refer to Table 6, noting that for inland areas of coastal southern California bougainvillea has a KS ranging from 0.25 to 0.30 according to one source and a KS ranging from 0.10 to 0.30 according to the other source.
  • You choose a mid-range value of 0.25 for now.
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