Horticulturist Thomas Ogren, author of five books, including Safe Sex in the Garden and Other Propositions for an Allergy-Free World (Ten Speed Press, Berkeley, 2003; $15; www.tenspeedpress.com or 800/841-2665), has created a system to rank the allergy-causing potential of many widely used landscape plants. Below are some trees that Ogren has found to be pollen-free or close to it; all are great choices for fall planting in the West. Visit www.allergyfree-gardening.com for more information on allergy-free gardening.

Alpine totara ( Podocarpus nivalis 'Green Queen' and 'Little Lady')

Box elder ( Acer negundo 'Variegata')

Chinese fan palm ( Livistona chinensis)

Eastern red cedar ( Juniperus virginiana 'Canaertii', 'Chamberlaynii', or 'Pendula Virdis')

English holly ( Ilex aquifolium 'San Gabriel')

Narrowleaf ash ( Fraxinus angustifolia 'Flame')

Paul's Scarlet hawthorn ( Crataegus laevigata 'Paul's Scarlet')