Fall Planting on the Palouse

by Pat Diaz, from the October 2004 Newsletter

Autumn is a great time of year to set out permanent plants in the Palouse region. Because spring is so temperamental and often short, spring-planted transplants can be exposed to freezing temperatures one day and hot summer weather the next. Plants put into the ground in fall have a better survival rate as they can become more established before the temperature extremes of spring and summer hit. In order to achieve strong root growth, however, you should get the plants in the ground before the ground freezes. October is usually the perfect month to get your permanent plants in the ground as well as your bulbs. First we’ll discuss where and how to plant and then finish up with good plant suggestions.

Location is an important consideration when choosing spots to plant your permanent plants. East- and north-facing exposures are good places for flowering trees as they have less chance of breaking dormancy and having blossoms damaged by late hard frosts in the spring.

To plant perennials from 4-inch pots, dig a hole the same depth as the container and 1-2” wider. Separate the roots and cut off any rootball coil that might be at the bottom. Place the plant so that the top of the rootball is even with the soil surface and firm the soil around the roots, watering gently. Spread a 3-4” layer of coarse compost or mulch over the root zone but don’t let it touch the crown of the plant.

To plant trees and shrubs that have been in containers, dig a hole twice as wide as the rootball and leave a little mound in the bottom of the hole for the tree/shrub to rest on. Again, have the rootball be at the same level as the surrounding soil. Backfill with amended soil and firm around the plant. Make a surrounding berm to form a watering basin and water slowly and deeply. Spread a 3-4” layer of mulch over the root zone.

TREES
There are some excellent choices of flowering trees to plant in the fall, including the native serviceberry. Some of the more popular trees include the crabapple Malus ‘Coralburst’, Eastern redbud (Cercis canadensis), European mountain ash (Sorbus aucuparia), Goldenrain tree (Koelreuteria paniculata), Ornamental pear (Pyrus calleryana), Pagoda dogwood (Cornus alternifolia), ‘Princess Kay’ plum (Prunus nigra), Russian hawthorn (Craetaegus ambigua), and Serviceberry (Amelanchier x grandiflora – ‘Autumn Brilliance’). All but the Russian hawthorn require moderate water while the hawthorn likes low water.

SHRUBS
Good choices for flowering shrubs include Apache plume (Fallugia paradoxa), Austrian copper rose (Rosa foetida ‘Bicolor’), Daphne x burkwoodii ‘Carol Mackie’, Dwarf chamisa (Chrysothamnus nauseosus) False indigo (Amorpha fruticosa), Fernbush (Chamaebatiaria millefolium), Golden currant, (Ribes aureum), Mock orange (Philadelphus lewisii), and Western sand cherry (Prunus besseyi). We have the latter three in our garden and they’re doing really well. Those requiring very low water are the Apache plume, dwarf chamisa, and fernbush. Those that like low water are the Austrian copper rose, false indigo, golden currant, and sand cherry. The remainder like moderate water.

GROUNDCOVERS
Good groundcover choices include Dwarf periwinkle (Vinca minor), Ice plant (Delosperma nubigenum), Rock soapwort (Saponaria ocymoides), Snow-in-Summer (Cerastium tomentosum), Speedwell (Veronica pectinata), and Woolly thyme (Thymus pseudolanuginosus). The periwinkle, speedwell, and thyme are fire resistant and like low water while the others prefer moderate water.

ORNAMENTAL GRASSES
Good grass choices include Blue oat grass (Helictotrichon sempervirens), Feather reed grass (Calamagrostis x acutiflora), and Little bluestem (Schizachyrium scoparium ‘The Blues’) which like low water, and Fescue (Festuca idahoensis ‘Siskiyou Blue’) and Maiden grass (Miscanthus sinensis ‘Morning Light’) which like moderate water.

PERENNIALS
There are many perennial choices that are good for transplanting in the fall. They include: Desert four o’clock (Mirabilis mutiflora), Provence broom (Cytisus purgans ‘Spanish Gold’), Sundrops (Calylophus serrulatus), Winecups (Callirhoe involucrate) which like very low water; English lavender (Lavandula angustifolia), Jupiter’s beard (Centranthus ruber), Mullein (Verbascum bombyciferum ‘Arctic Summer’), Ozark sundrops (Oenothera macrocarpa incana ‘Silver Blade’), Purple prairie clover (Petalostemon purpureum), Rocky Mountain penstemon (P. strictus), Salvia nemorosa ‘East Friesland’, Statice (Limonium gmelinii), and Yarrow (Achillea ‘Moonshine’) which like low water; Aster x frikartii ‘Monch’ and Golden columbine Aguilegia chrysantha (A) like moderate water. The lavender, columbine, and Jupiter’s beard are all fire resistant.

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