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Growing romaine lettuce: A guide from seed to harvest

While there are many different types of lettuce to grow in the garden or in a patio pot, romaine is among my favorites. Yes, I love a good buttercrunch lettuce, but nothing beats the thick, crisp leaves of a head of romaine. Their texture holds a creamy salad dressing like no other leafy green out there. Have you ever tried to put Caesar dressing on bibb lettuce? The results are limp and soggy. Thankfully, growing romaine lettuce is easy, and I recommend every gardener grow a few heads each season.

Romain lettuce is distinguished from other types by its upright growth, thick stems, and tight heads.

What is romaine lettuce?

Also known as cos lettuce, botanically speaking, romaine is Lactuca sativa var. longifolia. Instead of growing a round, bulbous head or a loose, leafy one, romaine lettuces grow upright heads with sturdy, elongated leaves that have thick midribs and are densely packed. Romaine is among the most popular lettuces for both home cooks and restaurants, but it’s also been the subject of a handful of E. coli breakouts over the last decade. There’s no better way to ensure the safety of your food than to grow your own, but of course that’s not the only reason to plant this wonderful salad green.

Full-sized heads of romaine lettuce are beautiful and easily obtainable, even for beginner gardeners.

Why you should be growing romaine lettuce

The reasons for growing romaine lettuce go far beyond food safety and its ability to hold a good blue cheese dressing. In my experience, romaine is more resistant to slug and snail damage. They much prefer softer-leaved lettuces in my garden. And, since the heads of romaine lettuce are narrow and upright, you can fit more plants in a given area than you can of the round-headed varieties that spread out wide.

The upright growth habit of romaine lettuce means you’ll be able to plant them more closely than other varieties.

Another benefit of growing romaine lettuce is its ability to stay cleaner. Low-growing, rounded lettuce types are closer to the soil. When it rains, dirt and grit splash up and into the leaves, making them a chore to clean. But, since romaine heads are upright and the crown of the plant is a good 8 to 10 inches above the soil, not as much dirt and grit enter the folds of the lettuce head, making them a snap to rinse off prior to eating.

One final reason to plant romaine lettuce is its heat and cold tolerance. Romaine lettuce is slower to bolt (go to flower) and turn bitter in the heat than many other types of lettuce. And, while all lettuces prefer the cooler temperatures of spring and fall, there are several varieties of romaine lettuce that tolerate surprisingly cold temperatures, affording you the opportunity to extend your harvest into the late fall and even winter if you have a cold frame, cloche, or floating row cover protecting them.

While you’ll only find green romaine lettuces in the grocery store, red- and speckle-leaved varieties, such as this ‘Flashy Trout’s Back’, are easy to grow in the garden.

Romaine lettuce varieties

While almost all of the romaine you find in the grocery store consists of the same few green-leaved varieties, there are dozens of types of romaine lettuce you can plant in your garden. Yes, many have green leaves, but there are also romaine lettuces that have wine-colored leaves and others that are bi-color or have deep red speckles on green leaves. Growing romaine lettuce at home enables you to grow some pretty fun varieties that you won’t find in the produce section. Here are some of my favorites.

Red-leaved romaine lettuces
• Pomegranate Crunch
• Intred
• Outredgeous

Bi-colored and speckled romaine lettuces
• Rouge d’hiver
• Truchas
• Flashy Trout’s Back

Green-leaved romaine lettuces
• Rainier
• Paris Island
• Little Gem

For late fall and winter harvests, I recommend ‘Winter Density’. And the one I grow every season, even in the summer, because it’s extremely heat tolerant is ‘Valmaine’.

There are many beautiful varieties of romaine lettuce. Here is a basket of several types from my garden.

3 ways of planting romaine lettuce

When it comes to growing romaine lettuce, you have three options for planting.

Option 1: Planting from transplants

The first option is to purchase transplants at your local nursery. This is a great choice for beginner gardeners or those who are not interested in growing from seed. You’ll be able to skip the “nervous parent” stage, but the downside is that you’ll be limited to growing only the romaine varieties the nursery has in stock. Still, if you’re just growing a handful of plants in a pot or the corner of a raised bed, purchasing a starter pack 4 or 6 plants from the nursery is a great way to start.

One of the easiest ways to grow romaine lettuce is from transplants purchased at a nursery.

Option 2: Starting seeds indoors

Another possible way of growing romaine lettuce is to plant seeds indoors under grow lights. Sow the seeds indoors about 10-12 weeks before your last expected spring frost. In my Pennsylvania garden, our last frost occurs around May 15th. If I count backwards 10 to 12 weeks from there, that means I can plant my romaine seeds sometime in late February or early March. Because lettuce is a cool-weather crop that tolerates spring frosts, the plants go out into the garden 4 to 6 weeks after the seeds are sown. That means the seedlings that grow from my late February planting, go out into the garden in early to mid-April. I’ll be harvesting them in May or early June, before the weather warms.

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When growing romaine lettuce seeds indoors, have your grow lights on for 14-16 hours per day and keep them just a few inches above the tops of the plants. Keep the seedlings regularly watered and fertilize every two weeks with a seedling-specific fertilizer. Give each seedling plenty of room to grow and pot them up into larger containers as they outgrow the previous one.

One important additional step when growing romaine lettuce seeds indoors is to harden off the seedlings before you plant them out into the garden. This process is a gradual acclimatization to outdoor growing conditions, rather than just throwing them to the wolves, so to speak. Take the seedling trays outdoors in the shade for a few hours a day, gradually increasing the amount of time they spend outdoors and the amount of sun they receive each day. Within about 10 to 14 days, the seedlings are outside full time. Once they are, they’re ready to transplant into the garden.

Lettuce seeds are small, so they can be difficult to plant. Only cover them lightly when planting.

Option 3: Planting seeds outdoors

Personally, I don’t fuss with planting my romaine lettuce seeds indoors. Instead, I sow the seeds directly into the garden about 6 to 8 weeks before our last spring frost (so here in PA, that means I start sowing lettuce seeds outdoors in late March or early April). Though they are tiny, romaine lettuce seeds are tough. They don’t mind cold soil one bit, they seldom rot in wet ground, and they don’t require any fussing. They are almost foolproof.

Sow romaine lettuce seeds about a half-inch apart. Barely cover the seeds after planting and water them in. Be careful not to wash the seeds away! Then, walk away and forget about them. If you live in a warm climate, such as the Southern U.S., I suggest growing lettuce in the cooler temperatures of winter, rather than in the spring or fall.

When the seedlings are an inch tall, thin them to a distance of 5 or 6 inches apart. If you’d like, you can transplant the culled seedlings to a new spot in the garden, being sure to space them properly. If you don’t thin, your romaine won’t form full-sized heads. Give them room, and they’ll reward you with large, succulent heads.

Thin romaine lettuce seedlings to a spacing of 6 inches. This gives the plants plenty of room to grow.

Growing romaine lettuce in the fall

If you garden in a climate with a hot summer and a cold winter, don’t just grow romaine in the spring. Plant a second crop of romaine by sowing seeds in the late summer for an autumn harvest. The ideal time is 6 to 8 weeks before your first expected fall frost. I sow the romaine seeds directly into the garden in mid to late August, but you may be able to find transplants for fall planting at your local garden center as well. Because the weather can still be quite warm in the late summer here, keep the seeds and plants well-watered.

Don’t forget to grow a fall crop of romaine lettuce, too. They enjoy the cooler temperatures of fall and early winter.

More tips for growing romaine lettuce

Here are a few additional tips for growing a productive crop of romaine.

  1. Amend the soil with finished compost before planting. If you don’t have a home compost bin, purchase bagged compost from a local garden center. Never use fresh manures on or near your lettuce crop – or any other vegetables for that matter (hello, E.coli!).
  2. Feed your romaine lettuce with an organic liquid fertilizer every two to three weeks. I use fish hydroslate or a general organic liquid fertilizer such as PlantFuel.
  3. To keep slugs from eating your crop, use an organic iron phosphate-based slug bait around the plants.
  4. Romaine is harvested as either baby greens or full heads. Baby greens are pinched or cut from the plant when the leaves are as young as 30 days. Leave the growing point intact, and you’ll be able to make multiple harvests of baby greens from the same plant. Or wait until the head reaches full size and then use a sharp knife to cut it off at the base to harvest.
  5. Though romaine lettuce is more heat tolerant than other types of lettuce, you’ll want to make your final harvests before hot summer weather arrives. Heat makes the leaves turn bitter.
  6. To extend your harvest into hot weather, cover the plants with garden shade cloth to keep them cool.
  7. To extend your harvest of fall-grown romaine lettuce, cover the plants with a layer of floating row cover or one of these other garden covers recommended by Niki.
  8. If aphids are worrisome on your lettuce crop, interplant with sweet alyssum. As noted in my book about science-based companion planting, Plant Partners, sweet alyssum blooms are very attractive to several different predators of aphids, including parasitic wasps, ladybugs, and hover flies.
  9. Romaine lettuce is easy to grow in a pot. Use high-quality potting soil or one of our DIY potting soil recipes found here. Make sure the pot holds 2 gallons of potting soil for every head of lettuce you grow in it. That means that if you want to grow three heads of romaine, choose a pot that holds 6 gallons of potting soil.
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Growing romaine lettuce is a fun and easy endeavor. The results are crisp, healthy, delicious, and well worth the effort.

What’s Next? Step-By-Step Guide on When to Harvest Cannabis

These last few months you have spent countless hours caring for your seeds and growing them into robust, mature flowers. This is an exciting and stressful time for new growers, as you aren’t quite sure what to do next. How do you know if your plants are done growing? Are they ready to harvest? These questions are vital to understanding when to harvest and to ensure that you end up with quality cannabis. That’s where we come in.

The average grow time for indoor marijuana plants is 3-5 months from seed to harvest. However, this process can take from 8 weeks to 7 months depending on the plant! That is a huge range, right? That is why understanding the harvest process is so important. You don’t want to waste weeks and months growing, only to harvest your plants too early or too late and risk ruining your crop.

Harvesting depends a lot on knowing your strains, and on trial and error, but we are hopefully going to try and mitigate the error factor.

For most strains there is a 2-3 week harvest window. Keeping them in the flowering stage can increase yields as plants often increase flower production once they “ripen”. Sometimes waiting an extra week or two to harvest can yield an additional 10-30%! Knowing when to harvest is essential in order to maximize the quality of your product. You didn’t work hard all these months growing healthy plants just to lose half of your THC or lose on potency by harvesting early.

More common strains such as Indica harvest after 8 weeks of flowering. On the other hand, Sativia takes 10 weeks from the flowering stage and strains such as Autoflower only require 10 weeks from seedling to bud. Given the range of strains and variation in phenotypes, plus different growing conditions and preferences of individual marijuana users, it is important to recognize when your plant is approaching maturity; fortunately, there are only really three things you need:

  1. Knowledge, which we are here to provide for you.
  2. A good pair of eyes for visual inspection
  3. Magnifying tool to give your eyes a closer look to get all the details

The first bit of knowledge you will need to remember for later is to always flush your plants prior to harvesting (we will explain this further). Secondly, you need to be able to evaluate if your plants are ready for harvest. There are two main methods you can use: The Pistil Method and the Trichome Method.


The Pistil Method is not as accurate but is a good starting point for anyone new to growing. In this method, the Pistils (hairs) of the plant are reviewed to determine when to harvest. The following picture shows a plant that still has a few weeks to go. As you can see by the fact that the majority of the pistils are still white and sticking out straight.

This next picture features a plant that is nearing harvest, but still not ready. This is shown by the fact that less than 50% of the pistils have darkened and curled.

There are two options when it comes to the best time to harvest using this method. The first is to harvest when 60-70% of the hairs have darkened. This will provide the highest levels of THC. The second is to harvest at an even higher point, when 70-90% of the hairs have darkened. This, on the other hand, will result in a more calming and anti-anxiety effect due to the THC turning into CBN.

As mentioned before, this method can prove inaccurate due to the fact that some strains may maintain white pistils even when ready to be harvested. Experience and research on your specific strain will help you to understand what to look for.


The second method is referred to as the Trichrome method. This is considered to be more accurate to determine if your plant is ready for harvest. This method requires a magnifying tool to allow you to inspect the trichomes to ensure that you harvest your buds when they reach the optimum THC levels.

These trichomes you are looking for have a similar appearance to that of little mushrooms as shown in the photo below.

There are also tiny and clear, hair-like trichomes without a mushroom head but you can ignore these are they don’t affect potency. We want that magical little ball on top of the trichome as this contains most of the plants THC and other potent components. These are difficult to see with the naked eye, so you will require some form of magnifying glass (such as a jeweler’s loupe or digital microscope) to check on them.

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There are a few stages of trichome development. The first is the clear stage, as shown above, in which the trichomes appear like dew drops. Right now, the trichomes aren’t ready for harvest as they haven’t gained enough potency.

In the next stage, trichomes become cloudy and have a more “plasticky” look to them. In this stage, the buds are still growing and has not developed fully yet. When they are at least 40% darkened they can be harvested to result in a more “energetic” or “speedy” high. If you want to yield the highest level of THC you need to wait until at least 50-70% of the trichomes are cloudy.

The highest level of THC is found when most of the trichomes are cloudy. This leads to the most intense high resulting in greater euphoria and pain-relief effects.

It can be difficult to tell the difference between clear and cloudy trichomes, especially when you are just starting out, but don’t stress. This is just part of the process and it will get easier with experience!

There is one additional stage for the trichomes, which results in the highest level of sedation. This occurs when the cloudy trichomes turn amber. This results in slightly less THC and more CBN. Once 70-90% of the trichomes have clouded (20% amber), the result is a more relaxing high that assists in reducing anxiety.

In short, if you an ‘in-your-head’ effect, than it is best to harvest when 40% of pistils have darkened and curled in and 50% of the trichomes are cloudy. For the “strongest” marijuana buds with highest levels of THC, harvest when almost all trichomes are cloudy. Lastly, for a more relaxing and anti-anxiety result, wait until at least some of the cloudy trichomes have darkened to amber. The more amber, the more relaxing. However you do not want all of your buds to be amber as this would mean your plant is overripe.

Do keep in mind which strain you are producing as that can also have an effect on trichome development. For example, Indica strains are heavier by nature and therefore, there may be no need to wait for them to turn amber. Sativia on the other hand, produce a more cerebral high and may need to wait until 25% or more of the trichomes have turned amber to get a better bake. In some strains, the trichomes will never turn amber and others might turn red or purple! So once again, it is always a good idea to consult your strain.

Flushing Your Plants

As previously mentioned, you need to flush your plants before harvesting. This helps to guarantee the quality and smoothness of your cannabis. A good rule of thumb is to start flushing your plant two weeks prior to it being ready for harvest. Flushing is a fairly simple process that uses plain water to remove any nutrients in the soil – which, believe it or not, significantly helps your harvest! Flushing excess nutrients forces your cannabis to use up whatever it has stored. In the end, this means that there will be no leftover nutrients to taint the use of the bud. However, if you flush too early, you will risk starving your plant and leaving it unhealthy.

Flushing is a simple process. Whenever you would normally feed your plant, you will want to flush it instead. All you need is untreated tap water – just make sure to double-check your pH levels. You will want to flood the soil with all the fresh water it can hold and then leave it for a few minutes to allow for the nutrients to get picked up. Then flood the soil again to move these nutrients away from your flower.

For home growers most likely use a potted method, you will notice that the water draining from the out the bottom will be dirty. During the flush, your plant can lose its color quite quickly. While a little yellowing is common, keep an eye out for yellowing on the sugar leaves/buds themselves as once this happens, your buds will start to deteriorate quickly. After the flush period, your plants should appear lighter than at the beginning.

New growers have a tendency to get overly excited and harvest too early. This is especially true for your first few crops while you’re still getting the hang of everything. Waiting can be hard, but the reward far outweighs the risk of ruining your product if you jump the gun. Plus, when you’re ready to harvest, consider using an automated trimming machine to take the stress out of the process.

Using both methods and researching your strain will make a big difference in the outcome. However, at the end of the day, only you will know your plants best.