Mid-October finally brought the Valley a taste of fall. A cold front pushed through with a little rain, and forecasters called for Phoenix highs near 80 and lows in the 50s. If you garden in Arizona, you know what that means: the outdoor growing season is starting, not ending.
The University of Arizona Cooperative Extension's fall vegetable gardening guide calls September and October good months to start seeds for cool-season crops like lettuce, spinach, carrots, radishes, kale, broccoli and chard, and says garlic can go in through November. It also has a tip every raised-bed gardener should hear: bagged soilless mixes don't hold up well for years in a raised bed, while real mineral soil, amended with compost, stays productive.
That's a soil science lesson hiding in your backyard. And with more than 108,000 Arizona students now using Empowerment Scholarship Accounts, according to KOLD, a lot of families are looking for hands-on science they can do at home. This week, let your kids find out what's really in your Arizona dirt, then turn a corner of the yard into a living garden lab.
What your kids will learn
Grades K–5
- What plants need to grow: sunlight, water, soil and space
- How different soils look, feel and hold water
- What makes a test "fair" (changing only one thing)
- Recording sprouts and growth with drawings and simple charts
Grades 6–12
- Soil texture, moisture retention and aeration, and why they matter to roots
- Independent, dependent and controlled variables
- Calculating garden bed area and volume and designing a planting layout
- Measuring and graphing plant growth, then drawing evidence-based conclusions
This week's activity: the Backyard Soil Showdown
You'll need a garden trowel, four clear plastic cups, a pencil for poking holes, bagged potting mix or compost, a measuring cup, a timer and a packet of radish seeds (they sprout fast and like cool weather).
- Dig a sample. Scoop two cups of soil from your yard. Desert ground can be rock-hard, so an adult may need to help loosen it. Have kids describe the color, smell and any rocks or roots they find.
- Do the squeeze test. Wet a spoonful of yard soil and squeeze it in your fist. Does it fall apart (sandy), hold together and then crumble (loamy), or stay sticky and smooth (clay)? Try the same with the potting mix and compare.
- Time the drainage. An adult pokes a few holes in the bottom of each cup. Fill two cups with yard soil and two with potting mix or compost. Pour the same amount of water into one cup of each and time how long it takes to start dripping out the bottom.
- Plant a fair test. Plant three radish seeds in each cup about half an inch deep. Label each cup, water them all the same amount and set them side by side in the same bright spot.
- Measure and graph. Check every day. Record when each seed sprouts and measure seedling height with a ruler. Older kids can graph average height for each soil.
- Decide like a gardener. After two weeks, ask: which soil would you put in a raised bed, and why? Compare your answer to the UA Extension advice above.
Take it further with two ready-to-go kits
The Soil Science Experiment Kit (4 Pots) ($39.90) turns the showdown into a full lesson. It includes four 3-inch peat pots, traditional potting mix, expandable coconut coir pellets and two seed varieties chosen for fast germination (sprouting typically begins in 3 to 7 days). Kids plant the same seeds in different growing media and different seeds in the same medium. You also get a 5-lesson curriculum for Grades K–5 or 6–12 with an experiment planning sheet, a side-by-side growth chart and a reflection page or lab report template, all emailed after purchase.
Ready to move the lab outdoors for the cool season? The Raised Garden Bed Plant Science Kit ($113.97) includes a 6 × 3 × 1 ft galvanized steel raised bed with an open bottom for drainage, five 3-inch peat pots with soil for starting seeds, and five seed varieties. Kids start seeds indoors, transplant them into their own bed, and track growth from seed to harvest. The curriculum and worksheets include a garden planning map, a growth tracking chart and, for older students, lessons on bed area, volume and spacing. Quick math check for your kids: 6 × 3 × 1 = 18, and that's how many cubic feet of garden soil you'll need to fill it (the included soil is only for the seed pots).
Join the growing community
Every kit purchase includes an invitation to Aardvark's Seed Planting For Little Hands, our private support group for students and families using our kits. After your order, request to join and we'll add you. Kids can post soil-test results, show off their first radish sprouts and raised-bed layouts, and swap tips with young growers from the Sonoran Desert to the Arkansas Ozarks and the West Virginia hills.
Start your cool-season lab this week
In Arizona, fall is when the garden wakes up. Dig a soil sample this weekend, run the showdown, and give your kids a garden bed of their own to plan for the months ahead.
