Growing Great Lettuce

‘Lettuce’ Introduce You… Everything you need to know about growing lettuce and the best salads in town!

We’ll get you harvesting more flavor and crunch from your lettuce patch.

New gardeners are often told to grow salad greens as an easy vegetable crop. This advice is likely linked to the shorter harvest time for most salad greens. But beyond that, lettuce can be tricky for us northern gardeners- especially as climate chaos keeps creeping in.

Lucky for us, we’ve got a salad-centric farmer as our guide. Meet Jesse Edgington of Edgie’s Veggies. He’s an organic urban farmer and salad slinger. He grows in zone 4 around the Twin Cities (you may have seen him at St. Paul’s weekly Farmers Markets) so he’s a pro at pushing the early and late ‘shoulder seasons’ and dealing with those high heat and humidity days that plague many a salad lover.

Here’s what I gleaned from spending a day on his urban farm to help you grow great lettuce.

Lettuce Is a Bit of a Diva

Lettuce wears its lungs on its leaves. Plants have a mechanism that shrinks their cells when it is hot, so even though a leaf looks wilted in the afternoon it may perk up in the evening. Waiting to water will help you keep the roots (only 6” deep) from getting waterlogged.

Here’s what we can do to help harvest luscious baskets of lettuce longer throughout the season.

Seed Selection

The best harvests start with the best seed varieties. There are so many varieties (Johnny’s Selected Seeds 2023 catalog sells 102!) that offer more crunch, better flavor and increased disease resistance compared to the limp lettuces we’ve all half-heartedly harvested. Check out my Seed Co + Catalog Roundup for smart salad seeds.

Look for traits specific to your needs like faster maturity, heat or cold tolerance, or being slow to bolt. Baby green blends can be ready to harvest in thirty days, while romaine heads generally take over sixty days to fully mature. 

Bolting is the natural process of a plant turning energy from plant growth to seed production. In leafy greens, this is triggered by higher temperatures. Once a plant has started to send up that central seed stalk, the leaves become bitter.  

Lettuce seeds will germinate between 35F–75F. The sweet spot is 65F, so this is one seed that does not appreciate a heat mat when starting indoors.

Soil Health

Because Jesse grows a LOT of lettuce in a small space (harvesting between 200–400 heads or 40–100 lbs per week in the summer), he works with a soil scientist who recommends specific nutrients based on in-depth soil tests.

For the home gardener he recommends following good basic soil principles. Jesse adds, “Starting with healthy soil will give you a leg up and allow you to plant tighter. Crop rotation also helps keep soil-borne diseases in check.”

 Soil Health Principles

•  Keep Soil Covered
•  Plant many diverse plant families
•  Disturb Soils as little as possible
•  Grow plants as long as possible throughout the season

With Lettuce, Timing is Key 

We can grow multiple successions of lettuces in zone 3, 4, and 5 with some planning. For example, starting seeds indoors in early April and transplanting them out under cover (a simple low tunnel or cold frame does wonders) can get you harvesting by the end of May. Continuing to sow seeds every few weeks or even once more by mid-May (directly sown or indoors) will mean more homegrown salads during the heat of summer. 

Jesse recommends to “transplant 3–4-week-old seedlings so there’s a bit of space under the outermost leaves,” to prevent bottom rot. “Lettuce is happiest growing when the temperature averages 66F,” says Jesse, “so most lettuces will bolt by mid-July without some shade cover.”

Begin starting lettuce seeds in August for fall harvests. Work backward from first frost dates, keeping in mind that most lettuces require 50–60 days to reach maturity. Most varieties of lettuce can survive temperatures as low as 20F. That said, surviving is different than thriving. They prefer to be kept above freezing, so providing some cover can keep you harvesting weeks later. 

You can also get a jump start on salads by growing them in containers that you can start inside, and move back inside if the weather turns nasty. Read my full article on Growing a Salad Container Garden.

And for spinach lovers check out my article on Growing Spinach!

Dealing with Heat and Humidity

Jesse shares, “We’ll often mist for a few minutes on hot summer afternoons to cool off the rows, but we need to do it early enough in the day, so the leaves dry off before nightfall. It is a little counterintuitive, but lettuce hates humidity.” 

Humidity can bring disease and lettuces get many of them: Bottom Rot, Downy Mildew, Fusarium Wilt, and Lettuce Mosaic Virus are the most common. A lot of work has been done to breed natural resistance to these issues, so read those seed packet descriptions as most seed companies will list these (BR, DM, FW, LMV) as either low or high resistance levels. 

Keep in mind that airflow is especially important when our goal is to eat the leaves and we want to keep the whole plant disease free.

Less Pests

Flea beetles are notorious for putting those ‘pin prick’ holes into arugula and radish leaves, and they enjoy lettuce as well. Their damage is mostly cosmetic, with leaves still safe to eat. Aphids feed at the heart of the plant, which is harder to catch so watch closely for signs of aphids early on.

Growing a pest-free garden isn’t an attainable or sustainable goal. But, as Jesse says, “Things can get out of balance so the best organic option for keeping pests from devouring our crops is covering them with netting.” 

There are distinctions between insect netting, row cover, and shade cloth and each has a role in growing great greens.

Row covers are typically a spun-bond (not woven) polyester material. These will trap heat, while letting water and light in but keeping bugs out. Shade cloth is woven to let heat escape but still cuts the sun exposure and therefore keeps the temperature down, and bigger bugs out as well. Insect netting will cast some shade and is designed to not let even the tiny insects through.

Each of these materials comes in different weights and lets in a different percentage of sunlight, air, and water. Jesse uses them all. As a home gardener, I have a medium-weight row cover and insect netting and switch between those two. And a few old sheets to add shade as needed. 

Harvesting Tips

Since lettuce is roughly 96% water, harvesting in the morning before the sun wilts it is best. You can submerge wilted lettuce leaves in cold water to plump them back up a bit. Jesse, admits that plastic bags are great when it comes to keeping lettuce fresh. Keep bagged lettuce in the refrigerator for up to two weeks.

Michelle’s Favorite Lettuce Varieties

All have a good, sweet flavor, and satisfying crunch and grow well in her zone 4 gardens.

• Iceberg –50 days
• Red Iceberg– Dark red, super crunchy ribs, decent bolt resistance
• Summer Crisp/Batavia – 45–55 days
• Canasta – A bronze-blushed plant that was crunchy and bolt resistant.
• Romaine/Cos – 50–60 days
• Intred – A ruby Colored Little Gem, great flavor.
• Winter Density – A Bib-Romaine that’s super cold hardy and slow to bolt

The lettuce family (Lactuca sativa) holds 30,000 distinct varieties of leafy vegetables. And many beloved salad greens aren’t even included in the lettuce family, like Arugula Eruca vesicaria , Mizuna (Brasica rapa), Kale (Brassica oleracea) and Chicory (Cichorium intybus). Truly endless options to fill that salad bowl!

Jesse’s Variety Spotlight

Salanova is the industry standard for local farmers because the leaves stay ‘baby’ sized and sweet while the plant continues to produce more leaves from the center. It is also an open-formed plant that helps keep diseases and rot at bay. It’s ready to harvest in 50–55 days. The yield is also reported to be 40% higher and holds longer once harvested. The Salanova are a hybrid and specific to the company, Johnny’s Selected Seeds– shop HERE.

You can find Jesse (and family) slinging salad from their farm stand at the downtown St. Paul AND Apple Valley Farmers Markets on Saturdays and online at edgiesveggies.com—which is also where you can sign up for their newsletter to get info on buying direct from their farm stand!

This article originally appeared in the Northern Gardener Magazine.

Dig Into Salad Season!
-Michelle