What to plant this week in Boulder, CO
Boulder gardeners are currently in the critical window just before your average last frost date of April 21, meaning you must wait until mid-to-late May to safely put out tender transplants. While the soil is likely still cool from our winter snowpack, this week marks the time to start cold-hardy crops like garlic and edamame indoors or in protected frames.
The next 7 days
Boulder, COGrowing in Boulder right now
- Our high-elevation soils heat up slowly; wait until after April 21 before planting warm-season favorites like zucchini and beans directly into the ground to avoid frost damage.
- Utilize our abundant sunlight by placing transplants on south-facing slopes, but be mindful that rapid spring warming can dry out young roots quickly in our thin topsoil.
- Our clay-heavy mountain soil benefits from generous compost mixing now to improve drainage before the heavy May rainstorms arrive.
Sow this week
No direct sowing windows open this week.
Transplant this week
Nothing is due to go out this week.
Harvest soon
41 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
- Lima Bean
- Lisianthus (Prairie Gentian)
- Loofah (Luffa)
- Malabar Spinach
- Nasturtium
- Okra
- Pole Bean
- 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 tops of zucchini and squash plants now to encourage more fruit development rather than just vines.
- Cut back dying foliage on basil and borage after heavy harvesting to promote a second, smaller flush of growth.
Pest & disease watch
- Watch for early-season aphids clustering on new growth of basil and nasturtiums as temperatures rise above freezing.
- Monitor for cutworms threatening young sunflower and bean seedlings germinating in open fields this week.
- Check for powdery mildew on late-planted squash varieties, which thrives in our cool, moist spring air.
Watering this week
Water deeply in the early morning to reduce evaporation while supporting heavy fruit production on melons and squash.
Pull any volunteer weeds immediately around your transplants like edamame and fennel before they compete for nutrients.
Boulder gardening questions
3Can I plant my basil and zucchini seeds outside right now?
No, wait until after the average last frost date of April 21 before planting warm-season crops directly in Boulder's ground. Starting them indoors or in cold frames is the safest bet to avoid a hard freeze.
What local pests are targeting my beans and corn right now?
This is actually late for traditional fall planting, as we need consistent cool soil temperatures; however, you can still force it indoors if it's dormant, though outdoor planting now risks winter heaving.
Are the warm-season vegetables listed like bush beans and sweet corn ready to harvest yet?
Not quite; while they appear on this week's harvest list for mature crops, new plantings will need about 60-70 days to reach full maturity after your mid-May transplant date.
Other cities in zone 6a
12See the full zone 6a guide → · Plan your Boulder garden in SproutGuide →