How to Harden Lettuce Seedlings and Why It’s Important

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So I started a hobby due to weekends in quarantine because of this pandemic. I discovered that “green thumb” is a myth and you can do all things as long as you do your research and never give up. I posted an article on how to germinate lettuce seeds fast, this time, I will be discussing how to harden lettuce seedlings and why it’s important. By the way, I am using hydroponics “kratky” system and my little greenhouse is already finished. Thanks to my father, I just purchased what he needed and it’s already up in two weeks time!

My little greenhouse

Related article: How to Germinate Lettuce Seeds Fast

Why Harden Lettuce Seedlings?

What I like about planting? It seems like I am taking care of my children. Those delicate newborn seedlings that I have to water everyday while wishing for the sun to come out. Sometimes, I am talking and singing to them like I am totally nuts! Honestly, I already have a reason to wake up so early in the morning.

So like a toddler who’s starting to walk, we need to guide these little ones and that’s hardening. UMD.EDU described hardening “as the process of exposing transplants (seedlings) gradually to outdoor conditions. It enables your transplants to withstand the changes in environmental conditions they will face when planted outside in the garden. It encourages a change from soft, succulent growth to a firmer, harder growth.”

After 15 days, we transferred the seedling plugs to the Styrofoam cups and it’s a bit tiring but fulfilling. One by one the delicate lettuce seedlings with about four leaves were transplanted to cups with cocopeat. UPLB provided detailed instructions on how to prepare seedling plugs since I used SNAP as nutrient solution for my hydroponics “kratky” system.

How to Transplant Lettuce Seedlings

Materials Needed:

Styrofoam cups (8 oz.)
Serrated bread knife or saw
growing media (coco coir dust)
bamboo sticks


Prepare the Styrofoam cups. Use a serrated knife or saw to make 4 to 6 slits (about 2-inch long on the side and including about 1/2 inch at the bottom)

Fill the holding cups with the growing media (about one inch thick)

Transplant a seedling from the sowing tray. Dig a hole in the middle of the growing media in the cup. Use the bamboo stick to uproot the seedlings from the sowing tray with care. Transfer only one seedling per cup. Lightly press the media around the base of the transplanted seedling.

Carefully water the seedling plugs.

How to Harden Lettuce Seedlings

Actually, hardening is not in the manual from UPLB but I just saw tutorial videos online so I followed it. I just thought that due to stress of transplanting the seedlings, it’s just right to let them rest for at least two days. Before I transfer it to the growing media, I did not water the seedling plugs but put it in a container with water mixed with 50% SNAP solution. (Sorry, not able to take pictures because we were in a hurry and so exhausted after!)

My husband and I started to transplant the seedlings around three o’clock in the afternoon and finished only about half of what we sowed then continued it the next day, same time. The reason of doing it in the afternoon is to not expose them to sunlight that may cause the seedlings to wither.

It’s a lot of work, we transplanted more than 300 seedlings! So that same day, I sowed lettuce seeds at used egg trays at home putting only two to three per slot. Since this is just merely a hobby, I will only do at least 100 seedlings per week. That first time, I was just worried that it may not germinate so I put a lot of seeds.

So when transplanting your seedlings, try hardening first because remember, the keyword is “gradual”!

A day after hardening

Follow MykMagazine and will let you know how my lettuce seedlings are doing using SNAP hydroponics “kratky” system. Hopefully they’ll turn out healthy and ready to harvest in three weeks! Can’t wait!

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