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Weed it and Reap – Fall Planting

By: Elizabeth Dickey, Education and Visitor Engagement Director | 10/07/2020

Fall is a wonderful time to add new perennial plants to your landscape.  Fall plantings adjust to their new surroundings, getting set to actively grow in the spring. 

Analyze your garden to find plants that should be moved, places where plants need replacing, and spots where you would like something new.  Consider adding out-of-the-ordinary bulbs such as anemone, foxtail lily (Eremurus), and Fritallaria.

Before adding new plants, evaluate your soil. Is it too sandy and does not hold much water?  Is it mostly clay and does not let air and water in? Compost mixed into your soil can help alleviate both problems and is good for your plants, unless they (like many Boise Foothills native plants) do not grow well in rich soil.  Plant roots grow when the soil temperature is over 40 degrees. Treasure Valley soils stay 40 degrees and above until November 1 on average.  Plants should do well if you put them into the ground by mid-October. Bulbs can be added until the ground freezes.

Dig holes twice as wide as the pot size or the root ball of a tree.  To keep the plant from being buried too deep, don’t dig deeper than the pot or root ball.  If the hole is deeper, the plant may sink lower than is ideal as the soil underneath compacts.  Watch for trees and shrubs buried too deep in their containers, though! Look for the “root flare”— the area of the trunk or crown that slopes down to the roots. This area must be slightly exposed above the soil. Remove your tree or shrub from the container, and loosen or spread out the roots. If the roots extend out far past the root ball, give them a nice haircut! Roots shouldn’t gather like a pile of wet spaghetti noodles under the plant—they should be cut to just barely extend past the root ball. Place it in the hole, add soil from where it’s planted and tamp it down gently.  Water thoroughly and deeply, allowing the soil surface to dry between waterings.  Water up to three times a week during warm weather and then taper off as frost approaches. Suggested flowers, grasses, and shrubs include hummingbird mint (Agastache), big bluestem (Andropogon gerardii), fountain grass (Pennisetum), syringa (Philadelphis lewissii) and fragrant sumac (Rhus aromatic ‘Gro-Low’).

Perennial and biennial seeds can also be added at this time.  Be sure to read the package to learn the requirements for good germination.  For example, certain seeds should not be covered by soil, others benefit from being rubbed with sandpaper, and some should be soaked overnight before going into the ground. Seeds are complex little creatures!

Although the selection may be greater in the spring, visit your local nurseries to take advantage of fall sales.  Talk to the horticultural professionals about their favorite plants and ask about their recommendations for placement and care. Our Horticulture Hotline is ready for your questions!

Call us at 208-275-8607. Happy planting!