Planting-window tool

How to time a planting

• Plant when the soil can be dug. Whatever the calendar says, wait out frozen or waterlogged ground. Iowa State University Extension's own dates "can vary by a few weeks from year to year, depending on the weather."
• Plant a bare-root sapling while it is dormant. It goes in before its buds swell, and within days of arriving. Bare-root trees on arrival covers the first hour and the first weeks.
• Spring is the surer season for bare-root stock. University of Minnesota Extension and the Morton Arboretum plant it in early spring, and Iowa State's forestry page still finds fall planting of hardwoods fairly good.
• Fall suits a potted or balled tree. The Morton Arboretum writes that "When air temperatures are cooler than the soil, new root growth is encouraged without new top growth."
• Give a fall planting six weeks before the ground freezes. The Morton Arboretum and UMass Extension both ask for them, so the roots grow while the soil is still warm.
• Plant evergreens earlier in the fall. University of Minnesota Extension says "Do not plant evergreens later than October", and UMass Extension plants pine and spruce "before the end of September while the soil is warm".
• Some trees are best planted in spring. Among the slow-to-establish trees the Morton Arboretum finds best planted in spring are bald cypress, American hornbeam, larch, magnolia, hemlock, sweetgum, tuliptree and willow. Choose a species, and its page's sentence shows whether it is one of them.
• Water a fall planting until the ground freezes. University of Minnesota Extension says to "Thoroughly water plants in late fall just prior to the soil freezing." The watering calculator gives the amounts.
• Check the spot as well as the season. The planting-site check compares the spot with what the species takes.
• Seed keeps its own calendar. The seed sowing planner dates the chilling, the sowing and the first seedlings for each species.
• Saplings travel in season. Live plants ship February to May and October to November. The shipping page has the details.

The spring window comes from Iowa State University Extension's Community Tree Selection, Planting, and Care Guide: "In Iowa, this is usually late March to early June and late August to mid-October". The calculator reads early, mid and late in a month as its 5th, 15th and 25th. Late March then falls 34 days before the median last spring frost of Iowa's zone 5, April 28, and early June 38 days after it. So a potted or balled tree's spring window runs from 34 days before your last frost to 38 days after it. For bare-root stock, University of Minnesota Extension writes "Plant them in early spring before growth begins". The Nebraska Forest Service plants seedlings "before the buds begin to swell". No source puts a date on the buds, so the bare-root spring window closes on the median last spring frost, the calculator's own reading.

A potted or balled tree's fall window is the Morton Arboretum's, which plants from "mid-August through mid-October" and finds that fall planting "offers advantages that may outweigh spring planting". Its How to Plant Trees and Shrubs says to "allow six weeks before the ground freezes". In the Arboretum's own zone of Illinois, mid-August falls 63 days before the median first fall frost, October 17, and mid-October 33 days before the first night at 20 °F, November 17. The calculator opens and closes your window by the same gaps. UMass Extension's Fall Planting asks for "at least six weeks to establish before the ground freezes", and its mid-October falls 35 days before the first 20 °F night in its own zone of Massachusetts. Iowa State's own fall closes 23 days before the first 20 °F night of Iowa's zone 5. Nebraska Extension in Lancaster County plants "from early September through late October", which closes 14 days before the first 20 °F night in its zone of Nebraska. The sources disagree, and the calculator follows the Arboretum, which ties its close to the ground freezing, as UMass does. In summer a potted tree can still go in: the Arboretum writes "Summer planting is possible, but requires a regular watering program to be followed."

A bare-root sapling's fall window follows Iowa State's Fall Planting of Bare Root Seedlings. With hardwoods, it finds that "success is fairly good when planted after October 1 and continuing into the fall until soil frost formation begins". The calculator opens it at leaf drop, read as the median first fall frost, and closes it at the median first night at 20 °F, read as when soil frost begins. Both readings are its own, and the seed sowing planner also ends its fall bed at the first night at 20 °F. The same page calls spring "the optimum time to plant bare-root material in Iowa". University of Minnesota Extension, the Morton Arboretum's Selecting and Planting Trees and Iowa State's garden pages plant bare-root stock in spring only. The Nebraska Forest Service writes "Fall planting is usually not very successful." The calculator keeps the fall window because the plant pages give one, from leaf fall until bud swell, and calls spring the surer season.

Where a winter brings fewer than 80 nights at or below freezing, the fall window runs on into spring. Clemson Cooperative Extension writes that "roots of ornamental plants in the Southeast continue to grow throughout the warmer fall and winter months". Nebraska Extension adds that "Tree root growth continues late in fall, until soil temperatures drop below 40°F." Across NOAA's weather stations, those with fewer than 80 freezing nights a year average a winter of about 40 °F or warmer. The line of 80 nights is the calculator's own reading of NOAA's figures.

The frost dates are NOAA's 1991 to 2020 U.S. Climate Normals, the median of the weather stations in your state and zone, as the seed sowing planner uses them. NOAA calls them "conventional 30-year normals". It also gives the dates that one year in ten beats on either side. Across 6,949 stations those sit a median of 14 to 16 days from the median frost dates, which is why a single year can run two weeks either way. A ZIP code finds its zone in the 2023 USDA map's ZIP listing and its state in the Census Bureau's ZIP code areas, and it never leaves this browser. Seed follows the seed sowing planner's rules. Its fall bed runs from mid September, or the first frost where that comes sooner, until the first night at 20 °F, and its spring sowing falls on the last frost after chilling.

A species' planting sentence is its own page's, word for word. Where the page plants it in spring alone, as the magnolia pages do, only the spring window counts for it, and the same holds for fall. The whole subject is in When to plant a tree, and a bare-root sapling's first weeks in Bare-root trees on arrival.

The address carries the planting-window tool's inputs, so a link opens it filled in, and Copy link on a result writes one: state (a state's two letters, such as OH), zone (a whole number from 1 to 13), stock (bare-root, potted or seed), species (a plant's slug, the last part of its page's address, such as white-oak). For example, /tools/planting-window/?state=OH&zone=6&stock=bare-root&species=white-oak.