What a difference 4 degrees make.

This year’s warmer-than-average winter has created a bumper crop of hardy offerings for the annual spring plant sales put on by local nonprofit groups.

Starts, seedlings and cuttings are growing bigger than usual for this time of year, which means buyers will have hardier plants to choose from.

One reason is that the root systems are more established. One example is the master gardeners’ guava cuttings, which rooted quickly. “They are bigger than our usual size” that go on sale in April, says Laura Mellow, the co-chair of their sale’s propagation committee.

Growers also are moving their plants earlier from the protection of the greenhouse to the outdoors, where they will get acclimated to the Tucson climate.

Civano Nursery, which supplies shrubs and trees to a couple of the upcoming plant sales, was already moving plants from its five acres of greenhouses into the field. Usually that move happens in mid-March.

“We’ve never done that before,” says co-owner Alex Shipley. “The benefit is they’re more hardy, so the sooner we bring them out of the greenhouse, the better it will be for the homeowner.”

Vegetables are responding the same way. Melissa Mundt, food-production education coordinator for the Community Food Bank of Southern Arizona, says, “Plants in the greenhouse are quite large. Previously we would have planted them (in the ground) in the middle of March.” Instead, the tomatoes are in the community garden now. And the container Italian sweet peppers and sweet basil will look lush for the Organic Garden Fair and Plant Sale.

Tony Sarah, horticulturist at Magic Gardens Nursery, may bring some seasonally rare starter plants to the fair, including eggplant, cucumbers and squash. Grower Lorien Tersey says she may bring cucumber plants.

Credit the warm winter . The normal temperature for December through February is 52.9 degrees. This year through Feb. 20, the average temperature has been 56.6 degrees, according to the National Weather Service.

Tucson International Airport reported only two isolated overnight lows of 32 degrees or lower in that period.

Mundt heard that some gardeners were able to keep summer tomatoes and chiles going through the winter. On the other hand, she’s heard reports that winter crops went to seed early.

There is a downside to the warm winter when it comes to the spring plant sales. Lee Mason, general services director for Tohono Chul Park, reports that his penstemons and other flowering perennials were issuing their colorful blooms early in February, well before the March sale.

“We may be past flowering by the time the plant sale comes,” Mason says. “People are less likely to buy something without flowers.”

Shipley and Sarah say stock has been flying off the shelves of their retail garden centers because warm temperatures encourage people to get out and plant.

But Sarah cautions giddy gardeners who want to get a jump on spring planting. On the calendar, it still is winter.

“While it doesn’t mean that the nights will be colder, the days could drop down to average temperatures,” he says, which makes it too cool for some spring planting.

And a frost or freeze can still happen. Local gardeners accept March 15 as the date when freezing temperatures are unlikely. That’s in about two weeks.

Suggests Sarah: “Don’t get rid of the frost cloth.”

Contact Tucson freelance writer Elena Acoba at acoba@dakotacom.net