Pool opening · State guide
When to Open Your Pool in Maryland
Last updated: July 15, 2026 · 9 cities covered
Maryland's opening calendar spans about 14 days. The earliest model date belongs to Baltimore (April 12), the latest to Germantown (April 26), and the statewide median lands on April 20.
Every date is the same model — two weeks ahead of the day the local 7-day mean temperature crosses 61°F — applied to each city's own NOAA normals station. Click through for the live water estimate, the full window, and the 12-step checklist.
| City | Open by | Window opens | 61°F crossing |
|---|---|---|---|
| Baltimore | Apr 12 | Apr 5 | Apr 26 |
| Columbia | Apr 17 | Apr 10 | May 1 |
| Ellicott City | Apr 20 | Apr 13 | May 4 |
| Frederick | Apr 14 | Apr 7 | Apr 28 |
| Germantown | Apr 26 | Apr 19 | May 10 |
| Hagerstown | Apr 25 | Apr 18 | May 9 |
| Salisbury | Apr 13 | Apr 6 | Apr 27 |
| Silver Spring | Apr 22 | Apr 15 | May 6 |
| Waldorf | Apr 24 | Apr 17 | May 8 |
Dates are typical-year model outputs, not forecasts — each city guide carries the live widget that tracks the current year against them.
How to use these dates
Each "open by" date is two weeks ahead of that city's own 61°F crossing — the day its 7-day mean temperature (highs and lows averaged, from the nearest NOAA 1991–2020 normals station) reaches the level where unheated pool water starts climbing toward the 65°F algae-growth zone. Opening inside the window means starting up in cold, algae-resistant water: a single label-dosed shock instead of a green-water recovery, and a shopping trip while Maryland stores are still fully stocked.
Dates are typical-year guidance, not forecasts. A warm or late spring shifts the real-world moment by a week or two in either direction — every city guide carries a live water-temperature widget that tracks the current year against these normals, plus the full 12-step opening checklist sequenced to its local window. New to the process? Start with the generic how-to-open guide and the chemicals shopping list, then come back for your city's dates.