FrostList

When to Winterize Sprinklers in Dover, DE

ON TRACK128 days until first 28°F freezeNov 16

Dover's median first 28°F hard freeze is November 16 (1991–2020 NOAA normals), and it can strike as early as November 3 — so winterize your sprinkler system in Dover by November 6. The early-odds date runs roughly 13 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first first 28°F freeze near Nov 16; local deadline about Nov 6. The live 10-day outlook loads here.

Local freeze dates for Dover

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Oct 23Nov 4Nov 18
28°F (hard freeze)Nov 3Nov 16Dec 3
24°F (severe)Nov 11Nov 30Dec 20

NOAA station: Dover · 1.3 mi away · 30 ft elevation.

Numbers for Dover come from Dover, 1.3 miles away at 30 feet, where the medians fall 32°F by Nov 4, 28°F by Nov 16, 24°F by Nov 30. The 28°F freeze has come as early as Nov 3 and as late as Dec 3, a 30-day spread. Spring's last 32°F freeze clears around Apr 4. Snowfall averages 13 inches a year, first reaching an inch near December.

In Dover, freezing nights (32°F) typically begin around Nov 4 and the first hard freeze (28°F) follows near Nov 16. The 32°F date swings from Oct 23 at its earliest to Nov 18 at its latest, near 26 days. The last spring freeze averages Apr 4 and as late as Apr 17, which sets the safe window for reopening outdoor water and de-winterizing gear. At about 13 inches of snow a year, the freeze — not snow load — is the thing to plan around.

Your sprinklers checklist

  1. Shut off the irrigation water supply at the main valve and, if you have one, the dedicated sprinkler shutoff inside the house.
  2. Turn off the controller or set it to the "rain" mode so valves do not open while the system is dry.
  3. Drain the mainline using the manual, automatic, or blow-out method your system was built for; most pros prefer a blow-out.
  4. Connect a compressor to the blow-out port through a proper adapter and run 40–80 psi, one zone at a time, until the heads mist and clear.
    Helpful gear: Air compressor blow-out adapter — Recommended pick
  5. Insulate the backflow preventer and any above-ground valves; this brass assembly is usually the first part to crack.
    Helpful gear: Insulated backflow preventer cover — Recommended pick
  6. Cap outdoor hose bibs with foam covers after the hoses come off so the last exposed fittings stay protected.
    Helpful gear: Foam outdoor faucet covers — Recommended pick
  7. Open the backflow test cocks a quarter turn so any trapped water has room to expand.
  8. Log the date and the psi you used; you will want the reference next fall.

What to have on hand

Air compressor blow-out adapter
Quick-connect fitting that mates a shop compressor to your irrigation line.
Recommended pick
Insulated backflow preventer cover
Pouch that shields the above-ground backflow valve from early frost.
Recommended pick
Foam outdoor faucet covers
Slip-on domes that protect hose bibs after you drain them.
Recommended pick
Portable air compressor
A modest pancake unit moves enough air to clear most home zones.
Recommended pick

What this means locally

Dover freezes close to Vineland (Nov 14) and close to Wilmington (Nov 15) — a reminder that even nearby towns differ by days. Statewide, Delaware prep dates run Nov 5 through Nov 6, which is why Dover gets its own number rather than a Delaware-wide average. The same freeze also decides when to protect your indoor pipes and winterize an RV if you own one.

Other winter jobs in Dover

Every task below is dated to Dover's own freeze and snow normals.

Frozen pipes → Oct 23Ice dams → Nov 15Car battery → Nov 16Snow blower → Nov 24Sump pump → Apr 4RV → Nov 6Boat → Nov 9Motorcycle → Nov 4

See the full Dover winter checklist, in order →

Frequently asked questions

What temperature freezes sprinkler pipes?
Standing water in shallow lines and the backflow assembly can start to freeze once air temperatures drop into the mid-20s for several hours. Buried mains are slower, but the exposed brass backflow preventer and above-ground valves are the parts that crack first, which is why the deadline is tied to the first 28°F freeze, not the first frost.
Do I need to blow out my sprinklers or just drain them?
It depends on how the system was installed. Manual or automatic drains work if the lines were pitched to low points. Most irrigation pros recommend a compressed-air blow-out because it clears water that drains miss, especially in flat yards. If you are unsure how your system drains, a blow-out is the safer choice.
What happens if I don't winterize my sprinkler system?
Water left in the lines expands as it freezes and can split the backflow preventer, crack valves, or break fittings. Repairs to a backflow assembly commonly run more than the cost of a blow-out. The damage often is not visible until you turn the system on in spring and find leaks.
How much does a sprinkler blowout cost?
A professional blow-out typically costs somewhere in the range of a modest service call, depending on the number of zones and your region. Buying an adapter and using your own compressor costs less over time, but you need enough air volume to clear each zone. Prices rise once the first freeze warnings appear, so book early.
When should I turn my sprinklers back on in Dover?
Wait until the last spring freeze has passed, which averages around Apr 4 here in the 1991–2020 normals. Turning the system on too early risks refreezing a charged line. Open the main slowly to avoid a pressure surge, then walk each zone to check for winter damage before you rely on the schedule.
Can I winterize sprinklers myself?
Draining and insulating are within reach for most homeowners. A blow-out is doable if you own a compressor that moves enough air and you use a proper adapter, working one zone at a time at safe pressure. If your system lacks a clear blow-out port or you are not confident, hiring a pro once is a reasonable call.

Data: NOAA 1991–2020 normals via Dover, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.