What to Plant in May in Sonoma County

May is one of the most productive months in the Sonoma County garden calendar — and one of the most consequential. The last frost risk is behind us, the soil has finally warmed through, and the dry season is gaining momentum. For gardeners and landscape managers across Healdsburg, Windsor, Santa Rosa, and the broader county, May represents a genuine turning point: the final window of reasonable planting conditions before summer heat locks the landscape into a holding pattern.

Get things in the ground now and they will root deeply, establish quickly, and reward you through fall. Wait until June and you will be fighting the clock, spending more water, and fighting transplant stress on plants that never had a chance to settle. This guide covers what to plant in May in Sonoma County, what to skip, and what maintenance tasks will define how your garden performs all summer long.

May in Sonoma County: What the Season Means for Planting

Sonoma County spans a wide range of microclimates, from the cooler, fog-influenced zones near the Sonoma Coast and Petaluma to the warmer inland valleys around Healdsburg, Cloverdale, and Alexander Valley. That difference matters in May.

Along the coast and in low-lying fog pockets, nighttime lows can still dip into the low 50s through mid-May, and afternoon temperatures may not push past the mid-60s on overcast days. In Healdsburg and inland areas — sitting in USDA Hardiness Zones 9b to 10a — daytime highs are regularly reaching the mid-70s to mid-80s by early May, with warm nights and soil temperatures comfortably above 60°F. That soil warmth is what matters most for warm-season crops and ornamentals.

For the purposes of this guide, we are primarily writing for the inland Sonoma County gardener in Zones 9a through 10b. If you are gardening closer to the coast, push your warm-season planting dates two to three weeks later and hold off on heat-loving crops until you are seeing consistent afternoon warmth.

Warm-Season Vegetables to Plant Now

If you have been waiting for the right moment to get your summer vegetable garden going, May is it. All cool-season risk is gone for inland Sonoma County. Soil temperatures are consistently warm enough to support germination and rapid establishment across every warm-season crop category.

Tomatoes: Transplant starts now without hesitation. Varieties like Early Girl, Cherokee Purple, Sun Gold, and San Marzano all perform exceptionally well in inland Sonoma County’s warm days and cool nights. Give them full sun, deep initial watering, and stake or cage at planting time — not after they have already flopped over.

Peppers and eggplant: Both require warmer soil than tomatoes and genuinely thrive when planted in May in Healdsburg-area gardens. Set transplants in the warmest part of your garden, amend soil with compost, and do not rush fertilization — let them settle for two weeks before feeding.

Basil: Direct sow or transplant now. Basil thrives in the same conditions as tomatoes and is extremely sensitive to cold; May planting in inland zones guarantees success where April planting sometimes disappoints.

Melons and corn: Both are direct-sow crops that need warm soil to germinate reliably. Plant watermelon, cantaloupe, and corn directly in the ground now. Give corn a block planting (at least four rows) for adequate wind pollination, and give melons room to run — six feet of spacing per plant is not excessive.

Cucumbers and squash: Also direct sow in May. Summer squash will produce almost immediately; plant two to three hills for more than enough production through September.

Summer Annuals and Perennials

May is peak transplant season for summer-blooming annuals and many heat-tolerant perennials. Garden centers across Sonoma County are fully stocked, and the conditions favor fast establishment.

Marigolds: One of the most reliable performers in Sonoma County summer gardens. Transplant starts now or direct sow seed — marigolds germinate quickly in warm soil. French marigolds work well in borders and vegetable gardens; African marigolds provide bold color in larger landscape beds. Both deter some pest species and tolerate heat.

Petunias: Transplant from 4-inch or 6-pack starts. Wave and spreading types work in containers and hanging baskets; upright varieties fill border edges well. Deadhead regularly to extend bloom through fall.

Celosias: Direct sow or transplant. Cockscomb and plume varieties thrive in the dry heat of inland Sonoma County summers and provide unusual texture and color from July through September.

Salvias (ornamental): A broad category with outstanding options for Sonoma County. Salvia splendens (annual, fire red) can be transplanted now. Perennial salvias including Salvia greggii, Salvia microphylla, and the popular ‘Hot Lips’ variety are best transplanted this month while temperatures are still manageable — they will bloom by summer and return reliably for years.

Zinnias: Direct sow zinnia seed now for summer color. They germinate in seven to ten days in warm soil and bloom six to eight weeks after sowing. Stagger two sowings — early May and late May — for continuous color through September.

California Natives: Plant Before the Heat Arrives

California natives are often thought of as fall-planting plants — and for good reason, since fall and winter rain helps them establish with minimal irrigation. But May can still work for select natives if you are willing to provide supplemental water through the first summer. The key is getting them in the ground before sustained heat arrives, typically late May through June in inland Sonoma County.

Salvia clevelandii (Cleveland sage): One of the most drought-tolerant and fragrant shrubs for inland Sonoma County. Transplant from a one-gallon container now, water in deeply, and provide supplemental irrigation every seven to ten days through the first summer. It will be largely self-sufficient by fall.

Arctostaphylos (manzanita): Several Sonoma County-appropriate species are available at native plant nurseries this time of year. Plant early in May before heat arrives, mulch heavily, and water deeply but infrequently to encourage deep rooting. Avoid overhead irrigation once established.

Epilobium (California fuchsia): A low-water perennial with brilliant orange-red flowers beloved by hummingbirds. Plant now, cut back hard after bloom, and it will return vigorously each spring. Excellent for dry slopes and erosion control.

Penstemon: Many penstemon species native to California and the broader western United States thrive in Sonoma County. Penstemon heterophyllus (foothill penstemon) and Penstemon centranthifolius (scarlet bugler) both tolerate the summer dry season well once established. Transplant from containers in early May.

Trees and Shrubs: Last Call Before Summer

May is the last practical month to install new trees and shrubs from nursery containers in inland Sonoma County before the summer heat window. Trees and shrubs planted in May still have six to eight weeks of moderate temperatures ahead of them — enough time to begin establishing root zones before the soil dries and hardens in July and August.

Fruit trees, ornamental trees, evergreen shrubs, deciduous flowering shrubs, and most groundcovers can all go in this month with reasonable success, provided you commit to a consistent irrigation schedule through the first summer.

June planting is not impossible, but it requires significantly more water, more attentive monitoring for heat stress, and carries higher failure risk for larger specimens. If you have been planning a planting project, May is the time to act.

Good choices for May installation include crape myrtles, Mediterranean herbs (rosemary, lavender, sage), ornamental grasses, evergreen ceanothus, and any fruit tree that has been growing in a container over winter and is ready to go in the ground. Avoid bare-root planting entirely — bare-root season is January through March for our region.

Bulbs: Gladiolus and Dahlias

Spring-blooming bulbs are finishing up, but the warm-season bulb season is just beginning. May is prime time to plant gladiolus corms and dahlia tubers in Sonoma County.

Gladiolus: Plant corms two to six inches deep (deeper in sandier soils) and four to six inches apart. For an extended bloom season rather than one massed display, stagger your plantings every two weeks from early May through mid-June. Gladiolus are excellent cut flowers and will bloom approximately 70 to 90 days after planting.

Dahlias: May is the ideal planting window for dahlias in inland Sonoma County. Soil is warm, nights are mild, and the plants will establish before summer heat pushes them into overdrive. Plant tubers four to six inches deep with the eye facing up. Tall dinner-plate varieties will need staking — place stakes at planting time to avoid damaging tubers later. Like gladiolus, staggering dahlia plantings through May into early June extends the show from late July through October.

Both crops prefer full sun, well-drained soil, and consistent moisture during active growth. Neither tolerates standing water around the crown — if your soil is heavy clay, amend generously or plant in raised beds.

What to Stop Planting in May

As important as knowing what to plant in May is knowing what to leave off the list. Cool-season crops that thrived through the winter and spring are signaling the end of their productive season.

Lettuce, spinach, arugula, and other salad greens will bolt — send up a flower stalk and turn bitter — as soon as temperatures climb and day length increases in May. If you still have these crops in the ground, harvest aggressively now. Starting new plantings of these crops in May is largely futile for inland Sonoma County; they will bolt before they produce meaningful harvests.

Broccoli, cauliflower, and cabbage started from seed now will not mature before heat causes them to fail. Leave these for a fall planting starting in August.

Peas: Your spring pea planting is likely finishing or already done. Do not start new peas in May — they need cool weather to produce and will struggle from the moment they sprout in warm soil.

Bare-root plants of any kind: That window closed in March. All bare-root planting should now be from container-grown stock.

Starting Your Summer Irrigation Schedule

May marks the beginning of the dry season management period for Sonoma County landscapes. Even if you received rain in April, the soil profile is drying from the top down and natural rainfall is effectively done for the season.

This month, transition drip and irrigation systems from winter dormancy to active operation. Check all emitters and heads for clogs, breaks, and coverage gaps before the heat arrives. Adjust run times to match the increasing evapotranspiration rates — what worked in March will be inadequate by late May.

For newly planted material (anything installed this spring), plan on deep, infrequent irrigation rather than frequent, shallow watering. Deep watering encourages roots to follow moisture down into the soil profile, building the drought resilience your plants will need by August. A general guideline for new plantings in inland Sonoma County: water deeply once or twice per week in May, adjusting as temperatures climb.

Established, drought-adapted plantings — native gardens, Mediterranean-style beds, mature shrubs — may not need irrigation to begin until June or even July depending on your specific site conditions. Observe before you water; overwatering established drought-tolerant plants in May is one of the most common mistakes Sonoma County gardeners make.

What Not to Skip This Month

May brings a short list of maintenance tasks that have outsized consequences. These are not optional if you want a healthy, productive landscape through summer and fall.

Mulching before heat arrives: Apply two to four inches of organic mulch — wood chips, shredded bark, or straw — around all planting beds, trees, and shrubs before temperatures climb above 85°F consistently. Mulch reduces soil moisture loss by up to 50 percent, moderates soil temperature, and suppresses weed germination. This single task reduces summer water use and stress more than almost anything else you can do. Keep mulch two to three inches away from plant crowns and tree trunks to prevent rot.

Fertilizing warm-season crops: Tomatoes, peppers, melons, and other heavy feeders benefit from a balanced fertilizer application at planting time and again six to eight weeks later. Use a slow-release granular fertilizer at planting and supplement with liquid fertilizer once plants are actively growing. Do not over-fertilize nitrogen early — this produces lush foliage at the expense of fruit development.

Staking tall plants: Tomatoes, dahlias, gladiolus, tall salvias, and delphiniums all need support before they need it, not after they have already fallen over. Set cages, stakes, and plant supports in May while you still have room to work around small plants.

Pest monitoring: Aphids, whiteflies, and spider mites all increase as temperatures warm. Check the undersides of leaves on roses, vegetables, and ornamentals weekly. Early intervention — a strong spray of water, insecticidal soap, or neem oil — prevents infestations from becoming overwhelming.

Planting and Installation Services from Geared for Growing

At Geared for Growing, we work with residential and commercial property owners throughout Sonoma County — from Healdsburg and Windsor to Santa Rosa and Sebastopol — to design, install, and maintain landscapes that perform through every season.

If May is the month you have been waiting for to get a new garden bed planted, a tree installed, or a seasonal color rotation refreshed, our team is ready to help. We understand the local timing, the microclimates across the county, and the plant palette that genuinely thrives here year after year.

Whether you need a full landscape installation, seasonal color changes, native plant conversions, or irrigation system start-up and adjustment, reach out to schedule a consultation. May moves quickly — contact us today and let us make the most of the planting season while it lasts.