When to Plant Vegetables in Westminster, CO
Westminster enjoys a moderate climate in USDA Zone 6a, offering a generous growing season that supports a wide range of vegetables. You can start cool-season crops outdoors earlier than colder zones and still have plenty of warm days for tomatoes, peppers, and squash. The key to maximizing your harvest in Westminster is succession planting — stagger sowings every 2–3 weeks to ensure a continuous supply of fresh produce from spring through fall. With proper planning, you can harvest vegetables for seven to nine months of the year, and even extend into winter with cold-hardy greens under row covers.
Understanding Westminster's Growing Seasons
Westminster's Zone 6a gives you two productive growing seasons: spring (March–June) and fall (August–November). Summer works for heat-tolerant crops (beans, corn, cucumbers, tomatoes, squash). Your last frost date is March 30 — all spring planting planning starts here.
The fall garden in Westminster often outperforms spring — less pest pressure, cooler temperatures, and a second chance at broccoli and fall tomatoes. Start fall garden planning in July.
What to Plant This Month in Westminster
May
Direct Sow Outdoors
Bean, Corn, Cucumber, Zucchini, Beet, Carrot
Transplant Outdoors
Tomato, Pepper, Eggplant, Basil, SweetPotato
Harvest
Lettuce, Spinach, Radish, Pea, Broccoli
Tasks
- Transplant all warm-season crops after danger of frost has passed
- Plant sweet potato slips after soil warms above 65°F
- Mulch all beds with 2-3 inches of straw or shredded leaves
- Begin regular watering schedule — 1 inch per week minimum
- Install tomato cages and pepper stakes at planting time
- Harvest spring broccoli heads before they bolt
Full 12-Month Planting Calendar for Westminster
| Month | Direct Sow | Transplant | Start Indoors | Harvest |
|---|---|---|---|---|
| Jan | — | — | Onion, Lettuce, Broccoli | Kale |
| Feb | Pea, Spinach | — | Pepper, Eggplant, Tomato, Broccoli, Kale, Lettuce | Kale, Spinach |
| Mar | Pea, Spinach, Lettuce, Radish, Carrot, Beet, Cilantro, Onion | Broccoli, Kale, Lettuce | Tomato, Pepper, Basil, Zucchini, Cucumber | Spinach, Kale |
| Apr | Pea, Bean, Carrot, Beet, Radish, Lettuce, Spinach, Corn, Cilantro | Broccoli, Kale, Onion, Lettuce | Zucchini, Cucumber, Eggplant | Radish, Lettuce, Spinach, Pea |
| May ← | Bean, Corn, Cucumber, Zucchini, Beet, Carrot | Tomato, Pepper, Eggplant, Basil, SweetPotato | — | Lettuce, Spinach, Radish, Pea, Broccoli |
| Jun | Bean, Corn, Cucumber, Zucchini | — | — | Lettuce, Pea, Radish, Bean, Zucchini, Cucumber, Basil, Beet, Carrot |
| Jul | Bean, Carrot, Beet, Lettuce, Cilantro | — | Broccoli, Kale | Tomato, Pepper, Cucumber, Zucchini, Bean, Corn, Basil, Eggplant, Beet, Carrot |
| Aug | Lettuce, Spinach, Radish, Carrot, Beet, Cilantro, Pea | Broccoli, Kale | — | Tomato, Pepper, Eggplant, Cucumber, Zucchini, Bean, Corn, Basil, Onion, SweetPotato |
| Sep | Garlic, Spinach, Radish, Lettuce | — | — | Tomato, Pepper, Eggplant, Carrot, Beet, Bean, Broccoli, Kale, Lettuce, SweetPotato |
| Oct | Garlic | — | — | Kale, Broccoli, Lettuce, Spinach, Carrot, Beet, Radish |
| Nov | — | — | — | Kale, Spinach, Lettuce, Carrot |
| Dec | — | — | — | Kale |
Best Vegetables for Westminster
These 10 vegetables are the top picks for Westminster's moderate climate (Zone 6a). Each one is well-adapted to the local growing season, frost dates, and soil conditions.
60-85 days · 10-15 lbs per plant · moderate
Companions: basil, marigold, parsley, carrot
Harvest: Harvest tomatoes when color begins to change from green to their mature color — they will continue to ripen on the counter. For best flavor, never refrigerate tomatoes; instead, place them stem-side down on a countertop out of direct sunlight. If frost threatens, pick all remaining fruit including green tomatoes and ripen them indoors in a paper bag with a banana.
70-90 days · 5-10 peppers per plant · easy
Companions: tomato, basil, carrot, onion
Harvest: Peppers can be picked green for a milder flavor or left on the plant to fully ripen to red, orange, or yellow for maximum sweetness and vitamin C content. Use sharp pruners or scissors to cut the stem rather than pulling, which can damage the branch. Frequent harvesting encourages the plant to produce more fruit throughout the season.
50-70 days · 10-20 cucumbers per plant · easy
Companions: bean, pea, nasturtium, radish, lettuce
Harvest: Harvest cucumbers before they turn yellow, when they are firm and dark green — overripe cucumbers become bitter and seedy. Pick slicing varieties at 6-8 inches and pickling types at 2-4 inches. Check plants daily during peak production, as cucumbers can double in size in just 24 hours and overgrown fruit signals the plant to stop producing.
45-80 days · 1/2-1 lb per plant · easy
Companions: carrot, radish, onion, strawberry, chive
Harvest: Use the cut-and-come-again method: snip outer leaves at the base when they reach 4-6 inches, leaving the central growing point intact to produce new leaves. For head lettuce, harvest the entire plant when it feels firm. Always harvest in the cool morning hours for the crispest leaves, and watch for bolting — once the central stem elongates, leaves turn bitter.
70-80 days · 1 lb per foot of row · moderate
Companions: tomato, lettuce, onion, pea, rosemary
Harvest: Harvest carrots when the top of the root reaches about 3/4 inch in diameter, which you can check by gently brushing soil away from the crown. Loosen soil alongside the row with a garden fork before pulling to prevent breaking the roots. Carrots left in the ground past maturity can crack or become woody, but a light frost actually converts starches to sugars and sweetens the flavor.
240-270 days (fall planted) · 1 bulb per clove planted · easy
Companions: tomato, pepper, lettuce, beet, carrot
Harvest: Harvest garlic when the lower 3-4 leaves have turned brown but 4-5 green leaves remain at the top — each green leaf represents one intact wrapper on the bulb. Dig rather than pull the bulbs to avoid breaking the stems. Cure bulbs in a warm, dry, shaded area with good air circulation for 3-4 weeks, then trim the roots and store in mesh bags or braids.
50-65 days · 1/2 lb per plant per picking · easy
Companions: corn, cucumber, carrot, lettuce, radish
Harvest: Pick green beans when pods snap cleanly and before seeds visibly bulge through the pod walls. Harvest bush beans every 2-3 days to keep plants producing, and pole beans every day during peak season. Never harvest when foliage is wet, as this spreads bacterial diseases between plants.
55-75 days · 1-2 lbs per plant per season · easy
Companions: beet, celery, onion, garlic, dill
Harvest: Harvest kale from the bottom of the plant upward, snapping or cutting the lower leaves and leaving the top rosette intact to keep producing. Kale is one of the few vegetables whose flavor actually improves after a light frost, which converts starches to sugars. In mild climates kale can produce leaves through winter and into the following spring before finally bolting.
24-28 days to first harvest · 1/2-1 cup fresh leaves per week per plant · easy
Companions: tomato, pepper, oregano, lettuce
Harvest: Pinch or cut stems just above a leaf pair to encourage branching — each cut stem will produce two new growing tips, creating a bushier, more productive plant. Always remove flower buds as soon as they appear, because once basil flowers, the leaves lose their essential oils and turn bitter. For the best flavor, harvest in the morning after dew has dried but before the midday heat.
45-60 days · 6-10 lbs per plant · easy
Companions: corn, bean, nasturtium, radish
Harvest: Harvest zucchini at 6-8 inches long for the best texture and flavor — larger fruit become watery and seedy. Check plants every other day because zucchini grows incredibly fast in warm weather. Use a knife to cut the stem rather than twisting, and leave about an inch of stem attached to help prevent rot.
Spring Vegetable Garden in Westminster
Zone 6a spring starts in earnest in March — direct sow peas, spinach, carrots, and beets as soon as soil reaches 40°F. Your last frost is March 30. Tomato transplants go out 2 weeks after that date. Don't plant tomatoes too late — summer heat slows production by July in zone 6a. Getting transplants in ground by mid-May gives plants 6–8 weeks of peak production before heat stress.
Fall Vegetable Garden in Westminster
The fall garden is Westminster's second season — and often the most productive. Start broccoli, kale, and cauliflower transplants indoors in late June for August transplanting. Fall tomatoes planted in July yield September–November with less pest pressure than spring. Direct sow cool-season crops (spinach, arugula, lettuce, beets, carrots) in August–September — these outperform spring plantings in quality and pest resistance.
Companion Planting Guide for Westminster
Companion planting maximizes your garden's productivity by pairing plants that benefit each other. These combinations are drawn from the top vegetables recommended for Westminster's Zone 6a. Planting companions together helps repel pests, attract pollinators, improve soil fertility, and make the most of limited garden space.
Common Vegetable Garden Pests in Westminster
Attacks: Tomatoes, peppers, eggplant
Identify: Large green caterpillar with white stripes.
Organic control: Handpick or apply BT spray.
Attacks: Zucchini, summer squash, pumpkin
Identify: Sudden wilting. Sawdust at stem base.
Organic control: Row covers until flowering. Inject BT into stem.
Attacks: Most vegetables
Identify: Clusters on undersides of leaves.
Organic control: Strong water spray. Neem oil. Ladybugs.
Attacks: Beans, grapes, roses, many vegetables
Identify: Metallic green beetle skeletonising leaves.
Organic control: Handpick into soapy water. Milky spore for grub control.
Soil & Growing Tips for Westminster
Moderate climates offer an excellent balance of season length and winter chill, making a wide range of vegetables possible. Take advantage of both spring and fall planting windows. Start cool-season crops outdoors in early March under row covers, and extend the fall season with cold frames. The moderate zone allows two full crops of lettuce, radish, and spinach — spring and fall — maximizing your garden's productivity throughout the year.
Seed Starting Guide for Westminster
Your last frost date in Westminster is March 30. Use this as your anchor date — count backwards to know when to start seeds indoors.
| Crop | Weeks Before Frost | Start Indoors | Transplant |
|---|---|---|---|
| Tomatoes | 8 weeks | January 18 | 1–2 weeks after last frost |
| Peppers | 10 weeks | January 4 | 2 weeks after last frost |
| Eggplant | 10 weeks | January 4 | 2 weeks after last frost |
| Broccoli | 6 weeks | February 1 | 2–3 weeks before last frost |
| Cabbage | 6 weeks | February 1 | 2–3 weeks before last frost |
| Cucumber | 3 weeks | February 22 | On or just after last frost |
| Squash | 3 weeks | February 22 | After last frost, soil warm |
| Basil | 4 weeks | February 15 | 2 weeks after last frost |
Based on average last frost of March 30. Actual dates vary year to year — keep frost cloth available until 2 weeks after your average last frost.
Vegetable Storage Guide for Westminster Harvests
Getting the most from your Westminster garden means knowing how to store each harvest. Improper storage is the most common post-harvest mistake.
| Vegetable | Best Storage | Duration | Key Tip |
|---|---|---|---|
| Tomatoes | Room temperature | 1–2 weeks | NEVER refrigerate — destroys texture and flavour |
| Garlic | Dark, dry, ventilated | 6–12 months | Cure 3–4 weeks before storage |
| Onions | Cool, dark, dry | 3–6 months | Don't store near potatoes |
| Winter Squash | Cool, dry | 3–6 months | Cure 10–14 days at 80–85°F first |
| Carrots | Refrigerator in damp bag | 4–6 months | Remove tops before storing |
| Sweet Potato | Dark, warm (55–60°F) | 6–12 months | Cure at 85°F for 7–10 days first |
| Peppers | Refrigerator | 1–2 weeks | Don't wash until ready to use |
| Beans | Refrigerate or freeze | 5 days fresh, 1 year frozen | Blanch before freezing |
| Lettuce | Refrigerator in damp towel | 1–2 weeks | Keep away from ethylene-producing fruits |
| Basil | Room temp in water | 1 week | Never refrigerate — turns black |
Common Garden Mistakes in Westminster
Even experienced gardeners make mistakes. Here are the most common pitfalls for vegetable gardens in Westminster's moderate climate and how to avoid them.
Waiting too long to start cool-season crops in spring
Fix: In zones 6-7, peas, spinach, and lettuce can go outside in early to mid-March. These crops tolerate light frost and actually grow better in cool weather.
Not starting a fall vegetable garden in late summer
Fix: Begin starting fall brassica transplants indoors in July, and direct sow fall lettuce, spinach, and radish in August for harvest through October and November.
Overwatering clay soils common in moderate zones
Fix: Add organic matter annually to improve drainage, and water deeply but less frequently. Use raised beds if soil is consistently waterlogged.
More Guides for Westminster
Frequently Asked Questions
When should I start planting vegetables in Westminster?
In Westminster (USDA Zone 6a, moderate climate), cool-season crops like lettuce, spinach, and peas can be direct-sown as soon as the soil can be worked in early spring. Warm-season crops such as tomatoes, peppers, and cucumbers should wait until the soil temperature reaches 60°F and all danger of frost has passed. Check the full 12-month calendar above for exact timing by month.
What are the best vegetables to grow in Westminster, CO?
The top vegetables for Westminster’s moderate climate (Zone 6a) include tomato, pepper, cucumber, lettuce, carrot. These varieties are well-suited to the local frost dates, heat levels, and growing season length. See the “Best Vegetables” section above for detailed profiles of each recommended crop.
What USDA hardiness zone is Westminster, CO?
Westminster is in USDA Hardiness Zone 6a, which is classified as a moderate climate for vegetable gardening purposes. This zone determines your frost dates, growing season length, and which varieties will thrive in your garden.
Can I grow a fall vegetable garden in Westminster?
Yes. In Westminster’s Zone 6a, cool-season crops like lettuce, spinach, kale, radishes, and broccoli can be planted in late summer for a fall harvest. Count backwards 60–90 days from your first expected fall frost to determine your last planting date. Many gardeners find that fall-grown greens taste sweeter because cool temperatures convert starches to sugars.
What companion planting combinations work best in Westminster?
Popular companion planting combinations for Westminster gardens include tomatoes with basil, corn with beans and squash (the Three Sisters), and carrots with onions. Companion planting helps repel pests, attract pollinators, improve soil health, and maximize space. See the companion planting guide above for specific pairings suited to Zone 6a.
When should I plant tomatoes in Westminster?
Start tomato seeds indoors around January 18 and transplant 2 weeks after your last frost (March 30). In Westminster's moderate climate, getting transplants in by mid-May gives the longest production window.
Can I grow vegetables year-round in Westminster?
With planning, nearly so. Westminster has a generous growing season of about 31 weeks, and cold frames extend this significantly. Winter-hardy crops like kale, spinach, and garlic can produce through most of winter with basic protection.