SIOUX CITY, Iowa (KCAU) – Several areas across Siouxland saw record lows in the teens and 20s this past Sunday, with Sioux City setting a new record of 21°. These unseasonably cold temperatures have likely left many wondering when we’ll be done with these freezing and sub-freezing temperatures.

This is especially important for those wanting to get their gardens planted or farmers looking to get crops planted in their fields.

Typically frosts can happen when the temperature falls below 36° and becomes more likely to be widespread as the temperature approaches and reaches the 32° mark. 32° and below is also when we start to see the risk for freezes develop as well with hard freeze potential when it hits 28° or below.

Usually the first freeze/hard freeze occurs across Siouxland sometime in the first few weeks of October, earlier the further north you go and a bit later the farther south you go. Rarely, the first freeze/hard freeze occurs in mid-late September.

Our first frost tends to occur a bit earlier, within the first few weeks of September.

However, our main concern right now is when will we see our final frost/freeze.

The final hard freeze (28° or colder), on average (1900-Current), occurs around mid-April, on or around April 16th here in Sioux City. However, final days with temperatures at or below final freeze threshold have occurred as early as March 21st back in 1925 and as late as May 29th in 1947.

The final freeze (32° or colder) overall typically occurs towards the end of April or the first week or two of May, on or around April 28th-April 30th here in Sioux City, though last days for temperatures conducive to final freeze have come as early as April 6th (1977) or as late as May 29th (1947).

In terms of final frost, that usually occurs by the early/mid May, with the average date of final frost in Sioux City occurring on or around May 10th. This also varies greatly, with the earliest final date of frost-level temperatures (36° or colder) occurring in Sioux City as early as April 5th. 1955 and as late as May 29th in 1947.

However, between 2000 and 2023, average final dates for frost/freeze threshold level temperatures have remained mostly the same, with average final 28° low temperatures in Sioux City occurring around April 19th, happening as early as April 8th (2010) and as late as May 16th (2014).

Average date of the final day with a low at or below 32° between 2000 and 2023 also remained largely unchanged, with average occurrence around April 30th, as early as April 12 (2016) and as late as May 22nd (2022). The earliest date has shifted just a couple of weeks later and the latest shifted earlier by a few days.

For final frost threshold temperature, the average date of final low temperature at or below 36° remained the same, occurring on or around May 10th. The earliest final date of frost-level temperatures in Sioux City, however, has shifted later into the month of April with the earliest date between 2000 and 2023 being April 21st (2000). The final date of frost-level temperatures, similar to freeze and hard freeze threshold days has shifted a few days earlier as well, with the latest day with lows 36° or colder occurring on May 22nd (2022).

All those statistics can essentially be summarized pretty simply.

Average dates of final hard freeze (28° or colder), freeze (32° or colder), and frost (36° or colder) potential have remained largely the same and can typically be expected between mid-April (hard freeze/freeze) and early/mid May (final freeze).

Early final freezes and frosts, however, are trending later in recent years and late final frost/freezes are trending earlier.

So what exactly does this mean for planting season?

Well, it’s probably not ideal to plant any sensitive vegetation just yet since we could very likely see at least a few more frosts and even another minor freeze or two before we finally see low temperatures above the freeze/frost risk threshold for the season.

Your best bet for planting would be to wait until at least after the first couple weeks of May (a good rule of thumb is to wait to plant outside until after Mother’s Day). However, for smaller home gardens, you could start planting smaller things, like flowers, tomato and pepper plants in pots that can easily be brought inside on nights when frosts/freezes threaten. For smaller, at home gardening, you could also start your seeds indoors over the next few weeks and then transplant to your garden after frost/freeze risk subsides.

For more information visit https://mrcc.purdue.edu/VIP/frz_maps/freeze_maps.html#frzMaps for interactive maps and climatological data on first/last frost/freeze dates.