Answer: The Kaffirboom Coral Tree (Erythrina caffra) is a large, spreading, semi-evergreen tree native to South Africa. At a mature height of 40'-60', with equal spread, you can expect the roots to extend at least as far out as the canopy. For this reason, I'd be concerned. While you may not have trouble with the drainfield for years, you can reasonably expect the roots to invade the drainfield, which will provide a rich source of nutrients and moisture. If your trees are young, you have an opportunity to relocate them before they do permanent damage to your drainfield.
There are really no recommended trees or shrubs to plant near your drainfield. Turfgrass is the best groundcover and shallow-rooted herbacious annuals and perennials are acceptable plants for near a drainfield.
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