Growing Hydroponic Lettuce


Hydroponic Lettuce
Difficulty Light EC Range pH Range: Time to Harvest
Easy 14-16 hours 0.8-1.2 5.5 - 6.8 4-5 weeks
Nutrient and Health Info - Varies by type, but key nutrients include Vitamin K, Vitamin A, Vitamin C, Folate and Potassium
Tips & Tricks - Plant 2-3 seeds in each 2" growing media and let them grow together to grow more lettuce in less space.


Lettuce is a cash crop when it comes to indoor gardening and hydroponics.  It grows quickly and easily, and can save real money over time when you replace store bought organic produce with homegrown produce from your iHarvest®. It generally takes 4-5 weeks to grow a full-sized head of lettuce from seed in the iHarvest.  And, if you only trim the mature outer leaves, it can grow the equivalent of a new head of lettuce about every 2 weeks after that.  In larger systems with 2" growing media, like the iHarvest®, you can plant and grow 2-3 seeds in each piece of growing media, and grow much more lettuce in the same amount of space. 


Lettuce is quite simple to grow from seed.   Consider using our Seedling Starter Kit, or simply using the paper towel method for great results. You can even sow your lettuce seeds directly in the iHarvest®.  Your seeds will be slower to develop seedlings, but you will still have a high rate of success.


Give your lettuce plenty of light for it to grow.  While lettuce will do well with less light than some other plants, exposing it to 14-16 hours of light per day will be best for your lettuce, as well as any other iHarvest® plants.  Don’t worry about your electric bills.  The iHarvest’s full-spectrum lights are highly efficient, and use only 36W of power each. 

EC Range:

Your iHarvest® comes with an EC tester.  EC stands for ‘Electrical Conductivity’ and it is a measure of the nutrients in your water solution.  When growing lettuce, you will want to keep your EC range between 0.8 – 1.2 for optimal growth, but you can go at least as high as 1.6 and still have great tasting lettuce.  Lettuce grows great with other plants that grow well in these EC ranges, such as basil, strawberries, lemon balm, parsley and peas.  When you increase the nutrients in your iHarvest® above 1.2, your lettuce is likely to continue growing very well.  It may even taste great to you, although others might find it slightly more bitter.

pH Range:

Your iHarvest® comes with a pH tester.  Adjusting your pH allows your plants to absorb the nutrients they need as efficiently as possible.  Keep your pH between 5.5-6.8 for optimal growth.


Lettuce is a leafy plant that does not fruit, so it’s going to grow great with an all-around hydroponic growing solution for greens.  Mix your growing solution in the reservoir until your EC is between the range of 0.8-1.2 and your hydroponic solution will just right for growing lettuce.  Remember to mix thoroughly, either by stirring your reservoir or letting the pump run for 15-minutes after adding nutrients, before measuring your EC.

Pruning and Harvesting:

Your lettuce will grow quite slowly at first, then sometime during the 3rd week it will begin to grow very aggressively.  Before long, you will be able to harvest the mature outer leaves of your lettuce, while keeping the smaller leaves on the inside and allowing them to grow.  This is a great way to consistently grow fresh lettuce fast. 

Time to Harvest:

You can begin to harvest lettuce as soon as the end of the 3rd week of growth, but it is best to wait until week four when your lettuce will be larger and stronger, and then begin harvesting the outer leaves. 

Instead of slowly pruning your lettuce as described above, you can also let your lettuce grow to a large size (~ 5 weeks) and harvest it all at once.  There’s nothing wrong with this, and some people prefer it.  However, slowly pruning the outer leaves of multiple lettuce plants will produce more lettuce for longer.

Eventually, your lettuce will begin to produce flowers.  This is called bolting, and unless you want to let your lettuce go to seed, it’s time to remove that lettuce plant from your garden and start over.  That’s because lettuce traditionally begins to taste bitter after it flowers.

One more thing…sometimes lettuce grown indoors can be a little bit limp.  That’s because it’s warm and sometimes even dry indoors.  Give your lettuce a 2-5 minute bath and ice water to reinvigorate it and have it tasting crunchy right away.  Keep it crunchy in the fridge by sealing it in a Ziploc bag.


Lettuce is so easy to grow, and it will save you money over the long-term.  Just compare the price of a head of store-bought romaine lettuce free of pesticides and herbicides to what you can grow with the iHarvest® over a year.  

Thanks for reading.  Don’t forget, IGWorks® and the Indoor Garden Works Group on Facebook are always here to help you grow.

Check Out Our Lettuce Recipes!

Let's grow together!