Grow lettuce through the summer without bolting with a little knowledge and preparation we’ll share with you. Imagine your own fresh lettuce this summer!
Homegrown sprouts are an excellent alternative to meat, especially for vegetarians and vegans. They are healthy and nutritious if grown, tested and sprouted right.
With a little knowledge and a tiny bit of preparation, you can grow lettuce throughout the summer without bolting. Imagine serving your own fresh-harvested, garden-grown lettuce throughout the summer!
Lettuce is a cool-season vegetable, meaning it grows best in temperatures around 60 – 65°F. Once temperatures rise above 80°F, lettuce will normally start to “bolt” or stop leaf production and send up a stalk to flower and produce seed. The leaves become bitter at this stage.
This is because the mainstay of our beloved salads is not a North American native, but an ancient part of our dinner table. Belonging to the daisy family, lettuce was first grown by Egyptians around 4,700 years ago. They cultivated lettuce from a weed used only for its oil-rich seeds to a valued food with succulent leaves that nourished both the mind and libido. Images in tombs of lettuce being used in religious ceremonies show its prominent place in Egyptian culture.
The earliest domesticated form resembled a large head of Romaine lettuce, which was passed to the Greeks and then the Romans. Around 50 AD, Roman agriculturalist Columella described several lettuce cultivars, some of which are recognizable as ancestors to our current favorites. Even today, Romaine types and loose-leaf lettuces tolerate heat better than tighter heading lettuces like Iceberg.
Two factors cause lettuce to bolt and become bitter – temperature and sun exposure.
The temperatures you are concerned about are both air and soil, as a lettuce plant (or any garden plant for that matter) tolerates a higher air temperature if the soil around its roots is cool and moist. Ensuring a cool and damp soil gives you more air temperature leeway. Because lettuce has wide and shallow roots, a drip system on a timer teamed up with a thick mulch keeps it happier in warm weather.
Shade is the third part to keeping lettuce growing vigorously later into warm weather. Reducing sun exposure lowers the heat to the leaves, but also to the soil and roots – creating a combined benefit. Deep shade isn’t good, but a systemallowing sun during the morning while sheltering the plants in the afternoon keeps your salad machines going much longer than you thought possible.
One last bit of knowledge. Most lettuce seeds become dormant (won’t germinate) as temperatures rise above 80°F, a condition called”thermo-inhibition”. This trait is a carryover from wild lettuce in the Mediterranean Middle East, where summers are hot with little moisture. If the lettuce seeds sprouted under these conditions, they would soon die out and the species would go extinct.
Thanks to research, there are some easy techniques to germinate lettuce seeds in warm weather – our article Improve Lettuce Seed Germination shows you how. Now you’ll be able to start lettuce when no one else can!
The three most effective elements in keeping your lettuce producing during warm weather are a drip system on a timer, a good bed of mulch and shade. Let’s look at each one and how they help.
Lettuce growing with mulch, shade & drip system
A drip system on a timer maintains moisture levels much more evenly than hand watering, and the timer can be set for how much and how often water is needed. Checking the soil moisture levels is easy – just push your finger into the soil up to the second knuckle. If the soil feels moist and spongy the moisture is perfect for lettuce. Adjust the number and length of watering each time up or down to maintain this level. From experience, we usually start the timer once a day for 10 minutes in the spring and go to 2 and sometimes 3 times a day for 10 minutes during the heat of the summer. As the weather cools down, we decrease the amount of water accordingly.
This minimizes water stress on all your garden plants, not just lettuce. When the roots have moisture, they can withstand the heat and drying effects better without losing health and slowing production.
A thick bed of mulch reduces moisture loss at the surface of the soil from heat and breezes. Here in central Arizona, it’s not uncommon to have a 15-mph breeze with 90°F+ with 5 – 10% humidity levels. Basically, we garden in a giant hair-dryer!
We use two inches of wood chip mulch, but straw also works well and some gardeners have good success with well-aged compost. With mulch, the soil moisture levels are at the top of the soil where it meets the mulch. Without it, the moisture doesn’t appear until you’ve dug down at least two inches, with three inches having the same amount of moisture as the surface does with mulch. Another benefit of wood chip mulch is it provides needed nutrients to the soil and encourages earthworms and other beneficial soil life as it decomposes. The beds where we’ve put wood chips down have three times the amount of earthworm activity as those that have only compost or nothing at all.
The third element is shade, which might seem daunting but is surprisingly simple to provide. Shade can be from various sources – a living trellis of cucamelon, vine peach or Malabar spinach; a row of tall sunflowers on thewest side of the bed; a container garden on the east side of the house or garage to capture afternoon shade, or a shade cloth structure on the west side of the bed or over a container or raised bed. Trees can also give partial shade – grow on the east side to take advantage of shade during the hotter, more stressful afternoons.
You might be thinking – this all sounds great, but does it work?
Here are two examples showing that it does:
The first example is a study conducted by Kansas City area growers in cooperation with Kansas State University and the Organic Farming Research Foundation.
This project was conducted to test practical methods for extending the production of cool season leafy greens into the hot summer months in Kansas City, where high temperatures normally terminate production of these crops from June through August.
We used high tunnels covered with 40% shade cloth, combined with drip irrigation and were able to produce crops of lettuce (10 cultivars) and Asian greens (5 types) throughout the summer. Trials were conducted at three locations, two of them working organic farms, and the other an agricultural experiment station in order to produce statistically valid experimental results.We produced higher yields of marketable quality lettuce and greens over multiple harvests throughout the summer compared to outside plots, which produced lower yields of poorer quality crops.
As a result of this project, both growers have continued with summer greens production, recognizing that adapted warm-season vegetables may be more profitable under hot summer conditions. *1
The second example is a two-season grow-out test by the Sacramento County Master Gardeners at their Fair Oaks Horticulture Center during the summers of 2015 and 2016.
Grow loose leaf varieties that are heat-resistant or slow-bolting, rather than varieties that form heads.
Provide shade. Use shade cloth or plant on the shady side of taller vegetables.
Don’t skimp on water. Keep lettuce growing fast to prevent wilting, premature bolting, and bitterness.
Mulch lightly with an organic mulch to retain soil moisture.
Use cut-and-come-again harvesting of outer leaves.
Make successive plantings with transplants to replace spent plants.
During the season, replenish soil nitrogen to encourage growth. We used a mild liquid fish emulsion fertilizer.
Inspect plants for insects and diseases. Hand pick and destroy destructive insects. Remove diseased leaves or plants.
Merlot- 42 days to bolting – Dense heads of ruffled red leaves
Jericho – 73days to bolting -Romaine variety from Israel. *2
Here’s a quick and easy way to shade any container, raised bed or row in your garden:
Simple lettuce shade structure
Use 1/2 inch PVC pipe from any hardware store. 1/2 inch is the least expensive and easiest to work with for this use.
Shade structure detail
Using PVC elbows, simply insert the tubing into the elbow and push the uprights into the soil at the edge of the planter or raised bed. No glue needed, so they can be taken down and re-used next season.
Planter with shade system
We used some leftover shade cloth from another project and cable ties to secure the shade cloth to the PVC tubing.
Shade cloth canopy
The front of the shade canopy is left loose so we can harvest easily.
Lettuce shade detail
The right half of the lettuce is shaded, with the left half getting shade as the day progresses.
Now you have the tools and knowledge, so plan on successfully growing lettuce after everyone else has given up this season! As your accomplishments are recognized and compliments roll your way – make sure to share your tools and spread the success.
Lettuce after 3 weeks of heat
Our lettuce looks amazing, considering we’ve had continuous temperatures above 95°F for the past 13 days and above 100°F for the past 9 days. The Sweet & Spicy Mix hasn’t slowed down and is robust, crunchy, and still sweet with no bitter flavors. The growth is easy to see, comparing to the above photos.
Lettuce after 3 weeks of heat – detail of leaves
Looking closer, it isn’t perfect. There are some small holes and some of the leaf edges are a little toasty, but these conditions are so far outside of lettuce comfort zone, it’s like growing on Mars!
Lettuce normally starts to bolt at 80°F, but this has not only survived, but thrived at over 100°F for more than a week and more than 90°F for almost two weeks, this is a technique you should try.
References
We’ve greatly enjoyed our own homegrown sprouts for the past several years. There’s just something about their fresh taste and crispy crunch that can be enjoyed any time of year, no matter the weather.
As with all our seeds, we make sure we know who our growers are and where our seeds come from. This is even more important with seeds used for sprouting as they are eaten directly as a food.
We chose our sprouting seeds supplier because of their commitment to the safest and healthiest seeds possible. They showed us their safety standards and testing protocols and we want to share them with you.
Growing your own sprouts at home is much safer than buying them off the shelf at a supermarket, and we’ll show you why.
-The safest sprouts are those you grow at home in a glass jar from a trusted, reliable source that screens the seed and tests both the irrigation water and sprouts for contamination.
-The next best is fresh sprouts from a local, trusted grower who buys their seed from a similar source as above.
-The least safe sprouts are from the supermarket where they have most likely been grown in a different state and trucked in. These sprouts are usually more than a few days old when they are first put on the shelves.
Sprouts are healthy, nutritious and are rich in vitamins, minerals, proteins, enzymes, bioflavonoids, antioxidants, phytoestrogens, glucosinolates and other phytochemicals. They are an excellent alternative to meat, especially for vegetarians and vegans.
Fresh Homegrown Sprouts
There are two main hazards associated with sprouts – E. coli and Salmonella. Both of these terms are used a lot, but what do they really mean? What are they and where do they come from?
From the CDC website:
“Escherichia coli (E. coli) bacteria normally live in the intestines of people and animals. Most E. coli are harmless and actually are an important part of a healthy human intestinal tract. However, some E. coli are pathogenic, meaning they can cause illness, either diarrhea or illness outside of the intestinal tract. The types of E. coli that can cause diarrhea can be transmitted through contaminated water or food, or through contact with animals or persons.”
From the USDA website:
“Salmonella is an enteric bacterium, which means that it lives in the intestinal tracts of humans and other animals, including birds. Salmonella bacteria are usually transmitted to humans by eating foods contaminated with animal feces or foods that have been handled by infected food service workers who have practiced poor personal hygiene.”
The best and surest method of reducing the risk of sprout seeds carrying bacteria is making sure the seeds are never contaminated. This starts with an ethical grower using good agricultural practices and organic standards. The next step is conducting rigorous testing, both in-house and independently.
Mung Bean Sprouts
The testing done on our sprout seeds is different than any other testing protocols for food. There is no acceptable “percentage of contamination”, as is often the case with other foods. If any bacterial contamination is detected, testing is stopped and the entire lot is rejected – sometimes 40,000 pounds or more.
To ensure the sprouting seeds we offer are as safe as possible, our supplier extensively tests both the sprouting water and the seeds to verify if any bacteria is detectable after harvest. Our supplier and an independent lab both do multiple tests to safeguard our health safety.
Current pathogen tests are considered to be 97% accurate in detecting contamination. Duplicate testing at both 48 and 96 hours brings the accuracy and confidence up to 99.91% each time, for a final accuracy of 99. 999919%!
As of early 2017, our supplier is the only company doing these extensive screening and testing protocols. The FDA is studying this protocol and has begun advocating its adoption by sprout companies for testing.
Initial Sprouts Screening Results
Screening includes inspecting the bags for any urine or feces contamination, any holes in the bags, insect larva or other contamination. Afterwards, the seed is carefully inspected with both a magnifying glass and microscope.
Each and every bag is screened – this particular lot had 860 bags, each one weighing 50 lbs. for a total of 43,000 lbs.
In-House Lab Spent Irrigation Water Contamination Test
A small sample of seed is taken from each bag and added to the overall lot sample. The entire sample is sprouted for 48 hours, increasing any potential bacteria level approximately 1,000,000 times over the starting amount, substantially increasing the probability of detection.
Next, the sprout runoff water is sampled and tested by the in-house lab. This is called “spent irrigation water”. A sample of the sprouts is crushed and tested for contamination also. These tests are done in accordance with government food safety and industry accepted protocols.
The lab tests for both Salmonella and E. coli 0157:H7 after 48 hours and again after 96 hours of culturing the irrigation water.
Both bacteria do most of their growth in the first 2 days or 48 hours. This is when the first test is performed, with the second test at 4 days or 96 hours. The second test catches any late developments that might be missed on the first.
Independent Lab Spent Irrigation Water Contamination Test
A separate, larger sample of spent irrigation water is sent to an independent lab for more extensive testing. The independent lab performs a more in-depth analysis on a wider range of pathogens than the in-house lab because of their higher level of equipment.
Notice that the independent lab tests for the top seven strains of E. coli, where the in-house lab tests for the most common one. The lab uses a food microbiology genetic detection system.
This is possible because the specific genes or DNA of the different strains of E. coli have been mapped, so they are specifically targeted during this testing. This gives better accuracy, repeatability, and confidence in the testing than any previous methods.
Independent Lab Sprouting Test
Next, the independent lab tests four pounds of randomly obtained sprouting seed from the shipment. Having an independent, third-party lab analyze the sprouting seeds gives an additional measure of confidence.
Storage Confirmation
Finally, the storage facility is inspected and documented. This ensures the cleanliness and food safety of how the seed is stored to avoid insect or rodent infestation or damage.
In a home environment with only one person in contact with the sprouting seeds, cleanliness and food safety is much easier. Here are a few tips for sprouting safely:
Now you know the steps taken to ensure the highest quality sprouting seeds are available so you can enjoy the taste and nutrition of sprouts with peace of mind.
Grow Lettuce in Summer
Grow lettuce through the summer without bolting with a little knowledge and preparation we’ll share with you. Imagine your own fresh lettuce this summer!
Homegrown Sprouts Safety
Homegrown sprouts are an excellent alternative to meat, especially for vegetarians and vegans. They are healthy and nutritious if grown, tested and sprouted right.