How to Grow Lettuce in a Tower Garden During Summer
Lettuce is naturally a cool-season crop, but that doesn't mean you have to stop growing it when summer arrives. With the right varieties and a few changes to how you manage your Tower Garden, you can continue harvesting fresh lettuce through warmer weather.
The challenge with summer lettuce isn't simply keeping the plant watered. Prolonged heat can cause lettuce to grow faster, become bitter or bolt — when the plant switches from producing leaves to producing a flower stalk and seed.
Variety selection, afternoon shade, reservoir management and adjusting how you plant and harvest can all help. Here's how we grow lettuce in a Tower Garden during hot summer conditions.
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1. Choose Heat-Tolerant Lettuce Varieties
Variety selection is one of the most important parts of growing lettuce in hot weather. Some lettuces tolerate warmer conditions and resist bolting longer than others.
Some of our favorite lettuce varieties for summer Tower Garden growing include:
Choosing lettuce varieties that are slower to bolt can extend your harvest during warmer weather.
What does it mean when lettuce bolts?
Bolting is the point when lettuce begins producing a flower stalk and preparing to make seed instead of focusing on leaf growth. Heat and other stresses can speed up this process, and the leaves often become increasingly bitter once bolting begins.
2. Plant an Extra Seed or Two for Loose-Leaf Lettuce
During cooler growing conditions, one lettuce seed per rockwool cube is often all you need. Summer is one time when we sometimes change that approach.
When growing loose-leaf lettuce during summer, we often plant two to three seeds per rockwool cube. This gives us more leaves per planting and lets us harvest smaller, tender leaves frequently rather than waiting for each plant to reach a larger size.
That can be especially useful in hot weather because you're able to harvest more lettuce before prolonged heat encourages the plants to bolt.
Harvesting loose-leaf varieties while the leaves are younger can work particularly well during hot weather.
3. Give Lettuce Some Afternoon Shade
Lettuce needs good light, but intense afternoon sun combined with high summer temperatures can add unnecessary stress.
If your Tower Garden is outdoors and you're experiencing very hot conditions, especially temperatures in the mid-90s and above, consider reducing the intensity of the afternoon sun.
- Position the Tower where it receives morning sun and some afternoon shade.
- Use shade cloth during periods of extreme heat.
- Watch the plants for wilting and other signs of heat stress.
- Continue providing enough light for healthy, compact growth.
The goal isn't to put lettuce in deep shade all day. It's to reduce the combination of intense sunlight and extreme heat during the hottest part of the afternoon.
4. Pay Extra Attention to Water and Nutrients
Your Tower Garden reservoir deserves extra attention during summer. Plants use more water in hot weather, and a low reservoir can change temperature more quickly than a full one.
Keep the Reservoir Topped Up
Check your water level frequently during hot weather and don't allow the reservoir to run low. Maintaining adequate water helps keep the system operating consistently as plants use more water.
Reduce Nutrients When Necessary
Full-strength nutrients can add additional stress during extreme heat. We often use half-strength nutrients in hot summer conditions and may temporarily reduce to quarter strength when conditions are especially severe.
Summer Tower Garden care
Lettuce isn't the only crop affected by extreme heat. For more hot-weather reservoir, nutrient and crop-selection advice, read our 10 Summer Tower Garden Growing Tips.
5. Understand Temperature, Humidity and the Heat Index
You may see a weather forecast showing an air temperature in the 90s while the “feels like” or heat-index temperature is well over 100°F. The heat index is designed to describe how hot conditions feel to people, so it shouldn't be treated as the actual air temperature around your plants.
However, that doesn't mean humidity is irrelevant to plants. Temperature, humidity, sunlight, airflow and water availability all influence how plants respond to hot weather.
Instead of using the human heat index as a cutoff for growing lettuce, watch the actual growing conditions and the plants themselves. Wilting, rapid bolting and changes in leaf quality are signs that your lettuce is experiencing stress.
Can lettuce grow when it's over 90°F?
It is possible to continue growing some lettuce varieties during periods when daytime temperatures reach the 90s, particularly with heat-tolerant varieties and good heat management. But lettuce remains a cool-season crop, and prolonged high temperatures increase the likelihood of bolting, bitterness and reduced leaf quality.
6. Move Your Tower Garden Indoors When Necessary
If outdoor conditions become too difficult for lettuce, growing indoors is another option. A Tower Garden with appropriate Tower Garden LED Grow Lights lets you grow lettuce without relying on summer outdoor conditions.
For indoor growing, provide approximately 14–16 hours of light per day, followed by a period of complete darkness. Keep the grow lights approximately 6–8 inches above the plant canopy, adjusting them as the plants grow.
Looking for complete lettuce-growing instructions?
This article focuses specifically on growing lettuce through summer heat. For planting, Tower placement, lighting, nutrients, harvesting and common problems throughout the rest of the year, see our complete guide to growing lettuce in a Tower Garden year-round.
Ready to Grow Summer Lettuce?
Choose lettuce varieties suited to your growing conditions and start from seed or with healthy live seedlings.
