What to plant this week in Boulder, CO
Boulder gardeners are officially in the wind-down phase as temperatures drop toward last year's average minimum of -10°F. With garlic ready for harvest and daikon radishes nearing peak crunch, this week is about pulling roots before the ground freezes hard after October 17.
The next 7 days
Boulder, COGrowing in Boulder right now
- High altitude air dries out plant tissues quickly; apply a thick layer of compost or straw mulch now to insulate shallow-rooted perennials against late frost snaps.
- The strong F5 tornadoes common in this valley can damage late-blooming tender crops; secure tall stakes and consider covering sensitive plants with row fabric tonight.
- Boulder's rocky, fast-draining soil holds little moisture during the dry spell before winter rains; water deeply once more to ensure roots have enough reserve for dormancy.
- Avoid planting anything new now as the window between the final frost risk around April 21 next year and hard freezes has effectively closed.
Sow this week
No direct sowing windows open this week.
Transplant this week
Nothing is due to go out this week.
Harvest soon
2 crops- Daikon Radish
- Garlic
Seasonal tips
- Apply fresh mulch now to retain soil moisture as temperatures rise.
- Test soil pH before adding any compost or amendments for new transplants.
- Keep a close eye on emerging seedlings to protect them from late spring fluctuations.
Pest & disease watch
- Monitor for late-season aphid swarms on broccoli and kale which can cause significant defoliation before harvest if not controlled with neem oil or insecticidal soap.
- Watch for slugs seeking out tender garlic greens after recent rainfall, as they thrive in the damp microclimates found in Boulder's creek drainages.
- Check seedlings for cutworms that may still be active during cooler nights, causing damage to any transplants left unprotected.
Watering this week
Water deeply but less frequently now that the soil is warming up, encouraging strong root development.
Harvest Daikon Radish promptly before the heat sets in to ensure the best crunch and flavor.
Boulder gardening questions
3When should I pull my daikon radishes before frost?
Harvest your daikon radishes now while the soil is still workable, as freezing temperatures will crack the roots and make them woody. If you have a small amount left, they can tolerate light freezes but must be dug up immediately if temps drop toward -10°F.
Is it safe to plant garlic bulbs this week in Boulder?
No, garlic should be planted now only if you are starting very early indoors or in heated greenhouses; outdoor planting for fall harvest typically happens in late August through September. The current cold snap is too severe for successful root establishment before winter.
How do I protect my vegetable garden from the upcoming hard freeze?
Cover your entire bed with 6 inches of straw or pine boughs to insulate roots against temperatures dropping to -10°F, especially important given our rocky soil loses heat quickly. Remove covers only after the danger of frost has passed in mid-October.
Other cities in zone 6a
12See the full zone 6a guide → · Plan your Boulder garden in SproutGuide →