This is USU Extension horticulturist Tom Beddes, based in Juab and Utah counties.
With the unprecedented warm weather we've been having this winter, I'm hearing that some gardeners are eager to get cool season crops like radishes, broccoli, and lettuce planted outdoors early.
I understand the excitement — fresh produce is hard to resist — but Utah's climate is just too unpredictable. Along the Wasatch Front, it's usually best to wait until mid to late March.
To plant in cooler areas like Logan or Heber, the timing is delayed by a couple of weeks, until early to mid April. You can plant earlier if you're using season extension tools like low tunnels or cold frames to protect plants from cold snaps, though.
When planting outdoors, another important factor is soil temperature. Cool season crops need soil temperatures of at least 40 to 45 degrees, and they perform better as soils warm a bit more.
You can check your soil temperature with an inexpensive kitchen thermometer. Insert it several inches into the soil and let it sit for a few minutes to stabilize.
If the soil is too cool, there are ways to warm it. Forming shallow furrows helps, because the soil at the top warms faster.
You can also cover the area with UV resistant black plastic secured with rocks or stakes. You can even run drip irrigation underneath the plastic before planting once the soil warms. Simply punch holes through the plastic and plant.
Radishes, spinach, lettuce, and mustard greens are some of the easiest crops to grow from seed. For broccoli, cabbage, and Brussels sprouts, though, you may get better results by planting transplants instead of seeding directly into the soil.
Regardless of when the calendar says it's time to plant, always check the extended forecast. If a cold spell is predicted, wait a few days.
A little patience now often means a better harvest later on.