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Protecting Heat Sensitive Herbs in Summer

As summer temperatures soar, heat-sensitive herbs like basil, cilantro, and parsley can struggle to thrive. But with the right care, you can keep your delicate herbs flourishing all season long.

Quick tips

Shade and adequate watering are key to keeping these herbs healthy.

  • Mulching around the base of the plants helps retain moisture and keep the roots cool.
  • Using light-colored mulch reflects sunlight away, protecting the plants from overheating.
  • Keeping an eye on the forecast allows gardeners to prepare for heatwaves.
  • Placing temporary shade, whether with garden cloth or larger companion plants, offers necessary relief from the intense sun.

Heat stress in herbs

When herbs experience heat stress, several problems can occur. Leaves might turn yellow or brown and become crispy. Growth can slow down or stop completely. In severe cases, plants may die.

Heat stress also affects the flavor of the herbs. For instance, basil and cilantro may develop a bitter taste.

Stressed plants are also more prone to pests and diseases, as their weakened state makes them vulnerable.

Heat sensitive herbs

Some herbs are more sensitive to heat than others. These herbs can be adversely affected by very hot or dry weather and should be monitored for heat stress:

  • Cilantro: Prone to bolting (flowering) quickly in hot weather, which affects leaf production and flavor.
  • Chervil: Delicate herb that wilts easily in high temperatures and prefers cooler, partially shaded areas.
  • Parsley: Can become bitter and bolt in intense heat, especially flat-leaf varieties.
  • Dill: Tends to flower quickly in hot weather, reducing leaf production.
  • Chives: May become dormant or stop producing in very hot conditions.
  • Mint: While hardy, it can wilt and lose flavor intensity in extreme heat.
  • Tarragon: French tarragon in particular struggles in hot, humid conditions and may die back.
  • Basil: Though heat-loving, extreme temperatures can cause leaf burn and affect oil production, reducing flavor.
  • Lemon Balm: Can wilt and lose its vibrant aroma in intense heat.
  • Lovage: Prefers cooler temperatures; leaves may yellow, and growth slows in high heat.
  • Sorrel: Leaves can become tough and less flavorful in hot weather.
  • Chamomile: Flowers may become less potent in extreme heat.
  • Borage: While tolerant of some heat, extreme temperatures can cause wilting and reduced flowering.
  • Angelica: Prefers cool climates; heat can cause poor growth and reduced flavor in leaves and stems.

Heat tolerant herbs

Other herbs are much more drought and heat-resistant, and can thrive in hot conditions. They should still be monitored, particularly during peak summer or drought events, but are less likely to need extra care than the ones listed above.

  • Rosemary loves full sun and dry soil.
  • Thyme does well even in rocky or sandy soil and doesn’t need much water
  • Sage can survive in hot weather and doesn’t mind poor soil.
  • Oregano loves full sun and can handle drought.

Protecting heat sensitive herbs

Creating a good environment helps keep your heat-sensitive herbs healthy during summer. Focus on finding the ideal spot, providing shade, and using mulch to maintain soil moisture.

Selecting the right location

When planning your herb garden, choose a spot with morning sun and afternoon shade.

Check for good air circulation. Good airflow helps to keep plants cool. Avoid planting heat-sensitive herbs near walls or other structures that trap heat.

Increase shade

Herbs planted in containers can be moved to shielded areas during the hottest parts of the day, or to locations which receive morning sun and afternoon shade.

Use shade cloths or garden nets to shield sensitive herbs planted direct in the ground. These materials let enough light through but block direct sunlight.

Consider planting taller companion plants on the south-western side of sensitive herbs to provide afternoon shade.

Mulching

Mulching helps maintain soil moisture and keeps the roots cool.

Use organic mulch like straw, bark chips, or compost to help retain moisture. Spread it around the base of the plants, about 2-3 inches thick.

Organic mulch breaks down over time and enriches the soil. It also suppresses weeds, which compete for water and nutrients.

Inorganic mulch, like gravel, can also be useful. Though it doesn’t break down, it still helps retain moisture and keeps weeds away.

Watering techniques for heat reduction

During hot summer days, proper watering helps protect heat-sensitive herbs.

Timing and frequency

Watering early in the morning is ideal. This ensures that herbs have enough moisture before the sun becomes too intense.

Evening watering is good too, as it allows water to soak into the soil overnight.

Watering herbs once or twice a day is usually sufficient during summer. However, it depends on the herb type and soil condition. For herbs in pots, check the soil daily. If the top inch feels dry, it’s time to water.

Keep in mind that overwatering can be as harmful as underwatering. Ensure proper drainage to prevent root rot.

Watering techniques

Overhead watering, like using a watering can or sprinkler, can cause water to evaporate quickly in the heat. Wet leaves may also increase the risk of disease.

Drip irrigation is a more efficient way to water herbs in the summer. It delivers water directly to the soil and roots. This method reduces water waste and prevents leaves from getting wet, helping to prevent fungal issues.