Revelling in Romaine lettuce

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Romaine lettuce has come a long way. Romaine was once just the “other” lettuce, the supermarket alternative to iceberg, and known for its role in Caesar salad. Then other types of lettuce came on the scene, such as butterheads and Batavians, mesclun mixes and more. Salad greens unrelated to lettuce, came onto the market such as claytonia, arugula, cress and mustards.

In 2018, consumers can pick and choose from many types of lettuce and salad greens at the farmers’ market and grocery store. For gardeners, the options are even greater. Johnny’s Selected Seeds, for example, sells 84 varieties of lettuce — just lettuce. That doesn’t include the many other types of salad greens or mixes.

Given all these alternatives, why grow romaine? It turns out there are more reasons than ever to grow romaine (sometimes called cos) lettuce. The standard romaine lettuce with large green leaves and crisp ribs is excellent in salads, on sandwiches and even as the gluten-free alternative to crackers and bread. Spoonfuls of tuna salad on individual leaves is a great summer lunch. Heads of romaine (whole or cut in half) can even be seared, grilled or barbecued for a sweeter salad; you can’t do that easily with leaf lettuce!

Much as the classic romaine is wonderful, growers and consumers can now pick from various varieties. These varieties come in shades of deep burgundy to pinkish, from light to dark green, and various combinations such as shading from green to pink leaves, red leaves with green ribs and burgundy speckles on green leaves. Wild Garden Seed, for example, offers 38 varieties of romaine lettuce, and if you can’t decide, the company also offers four different mixes of romaine varieties.

In addition to the large full-sized heads, which are often 10 to 12 inches high, you can grow mini-heads that mature at five to six inches high. At the farmers’ market, customers with small households or people who just buy for a meal at a time might prefer small heads to the full-sized heads that can weigh 1.5 to 2 pounds. Also, chefs can use mini-romaines for individual servings of seared Caesar salads. A great marketing tactic is to sell a package of three or five mini-heads of different colours.

Mini-heads offer a couple advantages. They mature quickly (often ten days before full heads) and can be planted at a higher density, resulting in many more heads per square metre of garden space. According to an article by Johnny’s Seeds, “You could sell the mini-heads for half the price of full-size heads, and still make almost three times the money over a 120-day period.”

Romaine lettuce can be marketed as a full-sized head, a miniature head, as baby leaf lettuce and as the heart. For heads, the outer ‘wrapper’ leaves are often removed and discarded. For hearts, you remove many more leaves to expose the lighter-coloured, tender, inner core. Baby leaf lettuce is harvested at around ½ to one inch from the soil when the plants are 4-5 inches tall. After cutting baby leaves, the lettuce will likely regrow and give you a second harvest. Romaine lettuce, particularly the whole heads, tends to withstand storage and handling better than leaf and some other head lettuces.

In the market garden, romaine offers growers several advantages. Harvesting heads is fast and simple. The leaves are upright so it is fast and simple to cut the stems. The growth pattern also helps protect the plant from pests. Slug damage is less likely in romaine than in Oakleaf or other leaf lettuces where the leaves are closer to the soil. The tight romaine heads also create a barrier to slugs and bugs inside the head. However, when conducting this trial I found that rabbits had a strong preference for romaine. Night after night, rabbits travelled through or next to beds of leaf lettuce to reach the romaine trials in the middle of my garden. Eventually, I fenced the romaine with chicken wire (inside the garden already fenced against deer).

Most varieties of romaine lettuce can withstand colder temperatures better than leaf and other head lettuce — particularly cold-hardy cultivars varieties including Rouge d’hiver, Winter Density, Outredgeous, Pomegranate Crunch and Winter Wonderland. On the other hand, most romaines don’t excel in greenhouse production largely because of their susceptibility to tipburn — the browning of leaf edges. Tipburn is caused by disruptions in the level of calcium, which is often triggered by temperature swings or changes in the level of soil moisture. 

Trial methods

For the trial, I planted 17 varieties of romaine. I excluded a few from this article because I couldn’t evaluate them adequately due to rabbit damage. I grew two crops of the 17 varieties with the goal of evaluating performance under warm summer conditions and cool fall conditions in New Brunswick. But with global climate change, weather conditions are unpredictable. With temperatures reaching 30C in September and over 25C in October, the second planting turned out to be a test of tolerance to heat, cold and dramatic temperature swings. When the weather got cold, I covered the lettuce with floating row cover and harvested the last crop in December.

I direct seeded the lettuce outside in early June and again in the last week of August. Starting in a greenhouse and transplanting out was another option. For one planting, I sowed the seed densely, later thinned, and used the early harvested plants as “baby leaf lettuce.”

For the information in the table, comparisons of tolerance to heat were based on which plants bolted first. For cold tolerance, I evaluated which varieties had the most marketable leaves after days of freezing temperatures (and temperature swings).

I didn’t expect much of a difference in flavour. I knew romaine lettuce grown in my garden always tasted better than any store-bought lettuce I was served in a restaurant but I thought that was simply because my lettuce was fresh and organic. A couple of times in the growing season, I picked a leaf of every variety and ate them while standing in the garden. Most of them tasted similar but there were a few standouts among the crowd.

Even after months of eating romaine lettuce, often two big salads a day, I could still eat more (and indeed started another crop of romaine in the greenhouse). Conducting the trial just strengthened my appreciation of the plant. The beauty of having such diversity available is that people can select first for their growing conditions — certain varieties are better suited for greenhouse vs outdoor production — and then choose the colour, size and leaf patterns they want.

The results of my trial are shown in the table. As with any trial, the results are site-specific. The description of performance and flavour is based on how well each variety did in my garden, in the particular (and strange) growing conditions of 2017. I hope the descriptions will encourage readers to consider trying a few new varieties of lettuce in the future.

Keep it cool!

Lettuce is a cool-temperature crop. Although it germinates best at around 20C, the preferred growing temperature is 15C. It can, however, germinate at much lower temperatures and even survive frosts. At higher temperatures, it is likely to bolt.

I provide shade for lettuce and spinach by strategic planting. When temperatures are still cool in the spring and early summer, I want the greens to have full sun to get started but have shade when weather gets hot later in the summer. So, I plant peas, pole beans or other tall plants on the south side of the greens. The spacing between the companion plant and the lettuce (and between lettuce plants) depends on whether I plan to harvest greens as baby lettuce or as full-sized heads. On a larger-scale, growers can use shade cloth.

For fall crops of lettuce and other heat-sensitive crops, starting the plants is more of a challenge because seeds are sown when the weather is hot. For these crops, I want shade for the first few weeks of growth in August and early September, and then I want more sun as the temperatures drop and days get shorter. So, I plant the lettuce in the shade of an existing crop and then harvest the other crop later. Cover crops are great for providing shade. I can plant the lettuce next to a nearly mature cover crop of oats or buckwheat, and then either cut or incorporate the cover crop a few weeks later.

To keep the seed a bit cooler, I plant late crops into furrows 1.5 to 2 inches deep before a few days of overcast, drizzly weather is expected without covering or tamping the seed. The rain washes enough soil over the seed to cover it and I feel that the furrows keep the soil a bit cooler (given that warm air rises and the furrow provides a bit of shading in the low light of late summer).

- Janet Wallace