What to plant this week in Boulder, CO
Boulder gardeners are in the final push before summer's heat fully sets in, with the last frost officially expected around April 21st and temperatures dipping near -10°F this winter. This week marks the perfect window to transplant your warm-weather crops like Zucchini, Bush Beans, and Sweet Corn as they begin their rapid growth phase into our short but intense growing season.
The next 7 days
Boulder, COGrowing in Boulder right now
- Our unique foothill terrain creates microclimates; check soil drainage carefully in valley bottoms where cold air sinks, while rocky slopes may need extra irrigation retention.
- With only about 15 inches of annual rainfall dropping mostly in spring and early summer, prioritize mulching transplanted vegetables like Celery and Malabar Spinach to conserve moisture against our dry summers.
- Boulder's alkaline soils can lock up nutrients for acid-loving crops; test pH before adding compost to beds where Parsnips or Garlic are being established this week.
- Late spring frosts still occur after the April 21 average, so use row covers over early transplants of Okra and Edamame until nights consistently stay above freezing.
Sow this week
No direct sowing windows open this week.
Transplant this week
Nothing is due to go out this week.
Harvest soon
45 crops- Basil
- Borage
- Bush Bean
- Cantaloupe
- Celery
- Cleome (Spider Flower)
- Cosmos
- Cowpea (Black-Eyed Pea)
- Cucumber
- Dahlia
- Edamame
- Fennel
- Flour Corn
- French Marigold
- Garden Verbena
- Garlic
- Ghost Pepper (Bhut Jolokia)
- Gourd (Ornamental/Bottle)
- Honeydew Melon
- Leek
- Lima Bean
- Lisianthus (Prairie Gentian)
- Loofah (Luffa)
- Malabar Spinach
- Nasturtium
- Okra
- Ornamental Sweet Potato Vine
- Parsnip
- Pole Bean
- Potato
- Pumpkin
- Roselle (Cranberry Hibiscus)
- Scarlet Runner Bean
- Shiso (Japanese Basil)
- Summer Savory
- Sunflower
- Sweet Corn
- Sweet Potato
- Thai Basil
- Vinca (Madagascar Periwinkle)
- Watermelon
- Winter Squash
- Yellow Summer Squash
- Zinnia
- Zucchini
Seasonal tips
- Succession sow bush beans and sweet corn every two weeks for continuous harvests through summer.
- Pinch back the tips of basil and okra to encourage bushier growth rather than flowering too early.
- Add a thin layer of straw or shredded leaves around heavy feeders like pumpkins and squash to retain moisture.
Pest & disease watch
- Aphid colonies often explode on young Sunflower and Marigold seedlings as temperatures climb into the 70s; check undersides of leaves daily for honeydew residue.
- Powdery mildew spreads quickly on Zucchini and Squash varieties in our humid springs if foliage isn't spaced well for airflow; water at soil level to avoid leaf wetness.
- Root maggots target transplanted Carrots, Celery, and Leeks in our sandy-loam soils; apply floating row covers immediately after transplanting to prevent egg-laying.
Watering this week
Provide about 1 to 2 inches of water per week, applying it deeply in the morning to reduce evaporation and disease risk.
Harvest zucchini and summer squash early in the day when they are most tender and flavorful for your table.
Boulder gardening questions
3Can I plant Garlic now in Boulder, or is it too late for the fall crop?
While we are currently past the ideal September window for garlic in Zone 6a, you can still attempt a 'green garlic' planting if soil isn't frozen solid, though yields will be significantly reduced compared to fall-planted bulbs.
My Sweet Corn and Watermelon seedlings look leggy after weeks indoors; how do I harden them off for our dry air?
Acclimate your corn and melon plants by gradually exposing them to Boulder's full sun and wind over 7-10 days, misting leaves during the hottest part of the day to combat rapid moisture loss before transplanting outdoors.
Is it safe to harvest my Cantaloupe and Honeydew right now given our current weather forecast?
Yes, if vines are healthy and fruits show full slip (easy separation from the stem), you can harvest immediately; however, wait a few more days for maximum sweetness unless frost threatens within 48 hours.
Other cities in zone 6a
12See the full zone 6a guide → · Plan your Boulder garden in SproutGuide →