Your September Garden Checklist for Santa Cruz County
September is the secret weapon month for Santa Cruz gardeners. While much of the country is winding down, our mild climate lets us launch an entirely new growing season. Coastal highs settle into the pleasant mid-70s, fog frequency decreases, and the slanting autumn light gives the garden a golden quality. UC Cooperative Extension identifies September as one of the two best planting months (along with March) for cool-season vegetables in central coastal California.
What to Plant in September
This is the most important cool-season planting month. Direct-sow lettuce (Jericho, Winter Marvel, Red Sails), spinach (Giant Noble, Tyee), arugula, mustard greens (Red Giant, Tatsoi), and turnips (Hakurei, Purple Top White Globe). Sow radishes (Watermelon, Daikon) as both a crop and a soil-loosening tool in compacted beds.
Transplant a second round of broccoli, kale (Lacinato, Red Russian), and cabbage for winter harvest. Set out onion and leek transplants. Plant garlic chives and parsley.
In all zones, this is the month to plant overwintering peas (Oregon Sugar Pod, Wando) that will produce through the cool months. Direct-sow fava beans (Windsor, Aquadulce) for a spring harvest and as a nitrogen-fixing cover crop.
Order bare-root strawberry plants, fruit trees, and roses for November and January planting. Popular varieties sell out fast.
What to Harvest in September
Late-season tomatoes continue ripening, and the flavor of varieties like Brandywine and Cherokee Purple reaches its peak as warm days and cool nights concentrate sugars. Pick all remaining peppers, both sweet and hot. String hot peppers for drying.
Winter squash and pumpkins are ready when the rind cannot be dented with a fingernail and the stem has dried and turned brown. Cut (do not pull) from the vine with a few inches of stem attached. Cure in the sun for a week before storing.
Apples ripen this month in mountain and inland areas. Harvest when the background color changes from green to yellow and the fruit separates easily from the branch with a slight upward twist.
Grapes (both table and wine varieties) are ripe across the county. Taste-test before harvesting the whole cluster.
What to Maintain and Protect
Begin reducing irrigation on established trees and perennials as the days shorten and temperatures cool. Summer vegetable beds still need consistent water until you pull spent plants.
Clean and organize the garden. Remove spent tomato cages, pull dead summer annuals, and compost healthy plant material. This is satisfying work, and it prevents overwintering pests and diseases from getting a foothold.
Sow a cover crop (crimson clover, bell beans, or a mix) in any bed that will sit empty through winter. Cover crops prevent erosion during the rainy season, suppress weeds, and add organic matter when turned under in spring. UC ANR's cover crop guidelines recommend seeding before the first rain for best establishment.
Top-dress perennial beds and fruit tree basins with 2 to 3 inches of finished compost.
What to Watch Out For
Late-season tomato diseases accelerate as morning dew increases. Early blight (Alternaria solani) causes brown spots with concentric rings on lower leaves. Remove affected foliage and improve air circulation. If plants are heavily diseased, pull them and compost in a hot pile or dispose in green waste.
Cabbage white butterflies lay eggs on newly transplanted brassicas. Row cover (floating fabric) is the simplest and most effective protection. Install it at transplanting time and leave it on until plants are well established.
Yellow jackets become aggressive in September as their natural food sources decline. They are attracted to ripe fruit and sugary drinks. Traps placed at the garden perimeter help reduce encounters. Do not swat at them near the nest, as they are more defensive this time of year.
Sudden autumn heat waves (Diablo winds) can scorch young transplants. Shade cloth and extra water for a few days is all that is needed.
This month: Plant at least one bed of cool-season greens before September 15. Greens planted now will produce through Thanksgiving and beyond.
For more help with cool-season gardening, check out our free California Cool-Season Planting Guide at Your Garden Toolkit.
