Where the timings come from

How a timing gets into the app

For each care task, we keep a short quote from a published source (for example, “The late dormant season (late winter to early spring) is best for most pruning”) and a note on how we turned it into a window around your frost dates. A script re-checks every quote against the live page, so a source that changes gets noticed. Where a source times something by bloom or by when the ground freezes, the window is our estimate and is marked as one in our review notes.

These are general guidance for your area, not a guarantee for every season. A late cold snap or an early spring can move things; trust the weather in front of you.

Plant-care publications

27 publications behind the care timings for 66 plants:

• Dividing irises Chicago Botanic Garden · Bearded Iris
• Pruning evergreen hedges Chicago Botanic Garden · Arborvitae, Boxwood, Yew
• Crape myrtle pruning Clemson Cooperative Extension (HGIC) · Crape Myrtle
• Pruning peaches & nectarines Clemson Cooperative Extension (HGIC) · Peach Tree
• Pruning shrubs Clemson Cooperative Extension (HGIC) · Azalea, Bigleaf Hydrangea, Bridal Wreath Spirea, Butterfly Bush, Climbing Rose (once-blooming), Eastern Redbud, Flowering Dogwood, Japanese Spirea, Mock Orange, Oakleaf Hydrangea, Rose of Sharon, Saucer Magnolia, Weigela
• Pruning flowering shrubs Colorado State University Extension · Viburnum
• Vegetable planting guide Colorado State University Extension · Beets, Broccoli, Carrot, Cucumber, Eggplant, Green Beans, Lettuce, Onion, Peas, Pepper, Potato, Radish, Spinach, Sweet Corn, Tomato, Winter Squash, Zucchini
• Gardening tasks for July Cornell Cooperative Extension, Tompkins County · Garden Mum
• How to overwinter roses Iowa State University Extension and Outreach · Climbing Rose (once-blooming), Rose (repeat-blooming shrub)
• When should I cut back my ornamental grasses? Iowa State University Extension · Ornamental Grass
• When should I divide my perennials? Iowa State University Extension · Bearded Iris, Daylily, Hosta, Peony
• When should I prune shrub roses? Iowa State University Extension · Climbing Rose (once-blooming), Rose (repeat-blooming shrub)
• Winter care of perennials in central Oregon Oregon State University Extension · Garden Mum
• Cutting down perennials in the fall Penn State Extension · Hosta, Purple Coneflower, Sedum (Autumn Joy)
• How and when to prune flowering shrubs Penn State Extension · Azalea, Forsythia, Lilac, Mock Orange, Rhododendron, Viburnum, Weigela
• Pruning and training home fruit trees to an open center Penn State Extension · Peach Tree
• Cut back perennials now or later? Purdue University Consumer Horticulture · Black-eyed Susan, Garden Mum, Peony, Purple Coneflower, Sedum (Autumn Joy)
• Growing blueberries in the home garden University of Minnesota Extension · Blueberry
• Growing grapes in the home garden University of Minnesota Extension · Grape
• Growing raspberries in the home garden University of Minnesota Extension · Raspberry (summer-bearing)
• Growing stone fruits in the home garden University of Minnesota Extension · Plum Tree, Tart Cherry Tree
• Oak wilt in Minnesota University of Minnesota Extension · Oak
• Planting the vegetable garden University of Minnesota Extension · Basil
• Protecting trees and shrubs in winter University of Minnesota Extension · Arborvitae, Boxwood, Yew
• Pruning hydrangeas for best bloom University of Minnesota Extension · Bigleaf Hydrangea, Panicle Hydrangea, Smooth Hydrangea (Annabelle)
• Pruning trees and shrubs University of Minnesota Extension · Apple Tree, Birch, Flowering Crabapple, Forsythia, Honeylocust, Japanese Maple, Japanese Spirea, Lilac, Red Maple, Saucer Magnolia, Serviceberry (Juneberry), Smooth Hydrangea (Annabelle)
• Garlic – fall is the time to plant University of Wisconsin–Madison Extension, Bayfield County · Garlic

Hardiness zones and frost dates

• USDA Plant Hardiness Zone Map (2023), by the USDA Agricultural Research Service (USDA-ARS) and the PRISM Group at Oregon State University. ThymeIt uses PRISM’s ZIP code zone tables, unaltered.
• NOAA NCEI U.S. Climate Normals, 1991–2020: the median last spring and first fall 32°F freeze dates for the weather station nearest each ZIP code.
• US Census Bureau ZCTA Gazetteer: ZIP code area locations, used to match a shared location to the nearest ZIP code.

Zone data credit: USDA Agricultural Research Service and the PRISM Climate Group, Oregon State University.