Sweet Peppers in Zone 4B — Mountain West

Sweet peppers are a worthwhile addition to any Mountain West garden. Their vibrant colors and sweet flavor brighten summer meals, and they’re incredibly versatile in the kitchen. Plus, there’s a special satisfaction in harvesting your own sun-ripened peppers after a long winter.

Growing peppers at high altitude does present some challenges, including intense UV and our short 128-day growing season. But with careful timing and a few tricks, you can enjoy a bountiful harvest. Starting indoors is key, and getting them in the ground at the right time sets you up for success.

You'll want to get your sweet pepper seeds started indoors from late March through mid April, about eight weeks before you plan to transplant them outside. Use seed trays or small pots filled with a good seed-starting mix. Sweet peppers need warmth to germinate well, so aim for a soil temperature around 75-80°F. A heat mat can be very helpful.

Place your seed trays under grow lights or in a very sunny window. Remember, our spring light is intense, even indoors, so don’t skip the supplemental lighting. Keep the soil consistently moist, but not soggy. Bottom watering is a great way to prevent damping-off disease.

Our late spring can be deceptive, with warm days followed by cold snaps. Starting indoors gives your peppers a head start and protects them from these temperature swings.

Transplant your sweet pepper seedlings outdoors from late May through late June, after the danger of frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade and increase the time and sun exposure each day.

Plant your peppers 18-24 inches apart in well-drained soil. Even in late May and June, we can get surprise hail storms and chilly nights, so consider using row covers to protect your young plants for the first few weeks. The row cover will also help to increase soil temperatures, which sweet peppers love!

Sweet peppers need consistent moisture to produce thick, sweet walls. In our dry Mountain West climate, that means paying close attention to watering, especially during the hottest part of the summer.

Water deeply whenever the top 2 inches of soil feel dry to the touch. This “finger test” is more reliable than sticking to a rigid schedule, as weather conditions can change quickly here. Aim to give your plants about 1-2 inches of water per week, either through rainfall or irrigation. Water at the base of the plants to avoid wetting the foliage, which can lead to fungal problems, although our low humidity usually keeps that in check.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, such as straw or wood chips, will help retain moisture in the soil and keep the roots cool.

While not always necessary, some sweet pepper varieties can get quite large and benefit from staking, especially when they're loaded with fruit. This is especially true in areas prone to strong winds.

The best option is to use sturdy stakes made of wood or metal. Install the stakes at planting time, placing them a few inches away from the plant's stem. As the plant grows, gently tie the stems to the stakes using soft twine or plant ties. This will prevent the branches from breaking under the weight of the peppers.

Pinching off the first few flowers that appear on your sweet pepper plants can encourage them to focus their energy on vegetative growth, resulting in stronger plants and higher yields later in the season.

Simply snip off the flowers as soon as you see them, usually early in the season. As the season progresses, you can remove any suckers (small shoots that grow from the base of the plant) to improve air circulation. Toward the end of the season, around mid- September, you might want to pinch off any new flowers that appear. This will encourage the plant to ripen the existing peppers before the first frost.

You can expect your first sweet pepper harvest from early August through mid September, depending on the variety and the weather. Peppers are ready to harvest when they reach their full size and color for the variety. They'll also feel firm to the touch. Remember, the longer you leave them on the plant, the sweeter they'll become.

To harvest, use sharp pruners or scissors to cut the pepper from the plant, leaving a short stem attached. Be careful not to damage the plant's branches. Sweet peppers are continuous producers, so the more you harvest, the more peppers the plant will produce.

As the first frost approaches, harvest any remaining peppers, even if they haven't fully ripened. Green peppers will still taste great, or you can try ripening them indoors by placing them in a paper bag with an apple or banana.

Here are some common issues you might encounter growing sweet peppers in the Mountain West:

Blossom Drop

• What it looks like: Flowers fall off without setting fruit. Small fruit yellows and drops.
• What causes it: Temperature stress. Our cool nights and occasionally hot days can disrupt fruit set. Low humidity can also contribute.
• How to fix/prevent it: Be patient – fruit set usually resumes when temperatures moderate. Provide afternoon shade during extreme heat. Keep plants well-watered. Hand-pollination can sometimes help.

Aphids

• What it looks like: Clusters of tiny insects on stems and leaf undersides, sticky residue, curled or distorted new growth.
• What causes it: These sap-sucking pests thrive in warm weather.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs. Insecticidal soap or neem oil works well. Avoid excess nitrogen fertilizer.

Sunscald

• What it looks like: White, papery patches on fruit exposed to direct sun.
• What causes it: Intense, direct sunlight, especially after pruning. Our high altitude and intense UV make this a real risk.
• How to fix/prevent it: Don't over-prune. Use shade cloth in extreme heat. If fruit is already exposed, drape a small piece of row cover over it.

Blossom End Rot

• What it looks like: Sunken, dark patch on the bottom of the fruit.
• What causes it: Calcium deficiency caused by inconsistent watering. Common with our dry climate.
• How to fix/prevent it: Water consistently. Mulch heavily. Avoid over-fertilizing with nitrogen.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall patterns create a unique set of challenges for sweet pepper growers. Consistent watering is crucial to combat blossom end rot and blossom drop. Intense UV radiation requires careful attention to sunscald prevention.

Good companion plants for sweet peppers include:

• Tomatoes: They enjoy similar growing conditions and can provide shade for each other.
• Basil: Repels pests like aphids and whiteflies.
• Carrots: Improve soil drainage and attract beneficial insects.
• Onions: Deter pests and improve overall plant health.
• Spinach: Acts as a living mulch, suppressing weeds and retaining moisture.

Avoid planting sweet peppers near:

• Fennel: Inhibits the growth of many plants, including peppers.
• Kohlrabi: Competes for nutrients and can stunt pepper growth.
• Brassicas (cabbage, broccoli, cauliflower): Attract pests that can also affect peppers.