Southern Arizona's cool season is here, and with it comes a question every desert gardener watches for: when will the first frost hit? According to the University of Arizona Cooperative Extension's November garden reminders for Pima County, the first frost sometimes arrives in mid-to-late November. Extension suggests having frost cloth or old sheets ready, moving cold-sensitive succulents to a protected spot, and watering most plants before a cold night, because moist soil helps store heat (cacti and succulents are the exception) (UA Cooperative Extension, Pima County November Reminders).
That same list says November is a time to sow beets, carrots, peas, spinach, chard, kale and turnips. So Arizona families are in a fun spot right now: it is planting season and frost season at the same time. That is a perfect setup for a real experiment about heat, plants and protection.
It is also a busy season for Arizona homeschoolers in general. More than 108,000 students now use the state's Empowerment Scholarship Accounts, and families are meeting up at curriculum swaps, including one planned in Pinetop this month (KOLD 13 News, Oct. 2026). Whatever path your family takes, hands-on science is one of the easiest subjects to bring outside.
What your kids will learn
Grades K-5
- What a seed needs to sprout: water, warmth and air
- Why a covered space stays warmer than the open air
- How to observe and draw a seedling as it changes day by day
- Comparing how different kinds of seeds look and grow
Grades 6-12
- The greenhouse effect: how sunlight is trapped as heat inside a covered space
- Tracking temperature and humidity inside vs. outside, then graphing the results
- Comparing germination time and germination rate across seed varieties
- How ventilation changes temperature and plant growth
This week's activity: the mini greenhouse heat test
You can test the greenhouse idea today with a clear plastic storage bin or a large clear salad container, two cups of moist soil, and two thermometers (any simple outdoor or kitchen thermometers will do).
- Make a prediction. Will a covered cup of soil stay warmer overnight than an uncovered one? By how many degrees?
- Set up two stations. Place both cups of soil side by side in a sunny spot outdoors. Push a thermometer into each.
- Cover one. Turn the clear bin upside down over one cup. Leave the other open to the desert air.
- Take readings. Record both temperatures in mid-afternoon, at sunset and first thing in the morning, when it is coldest. Have an adult help with early-morning checks.
- Add a second variable. On another night, try one dry cup and one watered cup, both uncovered, to test Extension's tip that moist soil holds heat.
- Graph and explain. Plot each reading on a line graph. Which cup stayed warmest? What does that mean for a seedling on a frosty night?
Ready to scale the experiment up to real garden size? The Walk-In Greenhouse Seed Starting Science Kit turns your backyard into a plant science lab. It includes a 15 × 7 × 7 ft walk-in tunnel greenhouse with a galvanized steel frame and a green PE cover, eight mesh windows and a roll-up front door for ventilation, five 3-inch peat starter pots, five different seed varieties and soil for the pots. Kids plant, then compare how each variety sprouts and grows, while older students track temperature and humidity inside vs. outside and test how opening the windows changes things. Grade-banded curriculum and worksheets (K-5 or 6-12) are emailed after purchase.
Want to fill the greenhouse with more of the cool-season crops Extension recommends? The Heirloom Vegetable Seed Science Collection includes 30 heirloom varieties and about 5,000 non-GMO seeds, including Detroit Red Beets, Red Core Carrots, Long Standing Spinach and Mixed Green Lettuce, plus its own curriculum and worksheets for germination trials across varieties.
Join the growing community
Every kit comes with an invitation to Aardvark's Seed Planting For Little Hands, our private group for families using our kits. Share your temperature graphs and sprout photos, ask questions and see what other young growers are discovering. With families in Arizona, Arkansas and West Virginia, your kids can compare a Sonoran Desert frost night with an Appalachian one.
Beat the frost and grow a lab
Frost season is just ahead in the low desert, and the cool-season planting window is open now. It is a great moment to let your kids find out, with real data, how a greenhouse works.
