Growing lettuce in a hydro tower: from seed to harvest
Lettuce is the perfect start into hydroponics. Here I show you how I let it germinate cool, raise it in the seedling station and harvest it in the tower after 4 to 6 weeks.
Why lettuce is the perfect start
I start everyone who is new to hydroponics with lettuce. It germinates quickly, needs little nutrient and shows you early whether your values are right. In the tower it’s ready to harvest after about 4 to 6 weeks, much faster than in soil. I grow 30 to 40 lettuces on one square metre, and the daily slug hunt disappears completely.
Lettuce drinks little, too. With lettuce only, a full reservoir lasts around 4 weeks. And because you can grow it both indoors under the lamp and outdoors, you have fresh leaves all year.
| Sorte: | Hersteller: |
Dünger, EC und pH
| Phase | EC (mS/cm) | Frankies Dünger | pH |
|---|---|---|---|
| Anzucht (erste Blätter) | 0,4 | 0,5 ml pro Liter | 5,5 bis 6,5 |
| Jungpflanze | 0,8 | 1 ml pro Liter | 5,5 bis 6,5 |
| Wachstum im Tower | 1,2 | 2 ml pro Liter | 5,5 bis 6,5 |
| Ernte | bis 1,6 | bis 3 ml pro Liter | 5,5 bis 6,5 |
Zeitplan und Beobachtungen
Pflege
- Samen in den Schlitz legen, leicht andrücken, nicht abdecken.
- Kühl keimen lassen, über 24 °C keimt Salat schlecht.
- Erst EC messen, dann pH.
- Nachfüllen mit fertiger Nährlösung.
- Abends ernten, dann ist weniger Nitrat im Blatt.
- Draußen bei Hitze Pumpe 15 an / 15 aus.
Blattläuse: sitzen im Herz und an Blattunterseiten. Mit Wasser abbrausen.
Trauermücken: kleine schwarze Fliegen an der Anzucht. Gelbtafeln aufhängen, nicht zu nass halten.
Falscher Mehltau: gelbe Flecken oben, weißer Belag unten. Für Luft sorgen, Blätter entfernen.
Schnecken: nur draußen ein Thema. Tower nicht direkt ins Beet stellen.
Mein Tipp für draußen: Ein feines Insektenschutznetz über den Tower stülpen.
Wasserwechsel und Messwerte
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| Datum | Wasser neu | EC | pH |
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| What | Value |
|---|---|
| Germination type | light germinator, just press seeds in, don’t cover |
| Germination temperature | about 15 °C, my table says 15 to 20 °C |
| Germination time | about 3 days for me, a little longer when cooler |
| Seeds per cube | 1 seed, 2 with weak seed |
| Move to the station | at about 2 cm with the first roots at the bottom of the cube |
| Move to the tower | from about 5 cm, when the roots are longer |
| pH value | 5.5 to 6.5, my target 5.8 |
| EC value (mS/cm) | seedlings 0.4, young plant 0.8, growth 1.2, harvest up to 1.6 |
| Water temperature | 18 to 22 °C, up to 24 °C still OK |
| Light indoors | 200 to 300 PPFD, 14 to 16 hours |
| Harvest | after about 4 to 6 weeks in the tower |
You’ll find all values to print on my lettuce growing card. Tap “Print growing card” there and fill in your own dates.
My tip for your lettuce
Harvest lettuce indoors all year: the HydroFlex Tower Classic 6+
17 litre tank, room for 18 plants and more, and a look that suits the living room too. Just right if you want to harvest fresh lettuce regularly.
Your growing plan
Here you can see all five steps at a glance: tap a step and you get the values, the tasks and what you need right now. Below I explain each step in detail.
Step 1 · in the seedling box
Let lettuce germinate bright, shallow and cool
- One seed per cube, two only with weak seed.
- Put the seed in the slit and press lightly, don’t cover.
- About a third of the mat stands in water.
- Cover with film or spray from above daily.
- Grow light 14 to 16 hours a day.
Not too warm: Above 24 °C lettuce germinates worse, above 25 °C often not at all. The lamp warms things up too.
What you need now: my seedling box with 25 cubes and 10 lettuce seeds or for many plants the seedling mat with 100 cubes.
Detailed in the guide ›Step 2 · in the seedling station
Now the young plants need light and air
- Transplant at about 2 cm with the first roots at the bottom of the cube.
- At first the pot dips at most 0.5 cm into the water.
- Once all have 2 to 3 cm roots, lower the water: about 1 cm of air.
- Seed leaves open: 0.5 ml nutrient per litre (EC 0.4 to 0.6).
- From 2 to 3 cm: 1 ml per litre (EC 0.6 to 0.8).
- Always set the EC first, then the pH.
Good to know: The millilitres apply to my liquid nutrient. What matters is the EC your meter shows.
What you need now: my seedling station for 25 plants, net pots and Frankie’s liquid nutrient.
Detailed in the guide ›Step 3 · in the HydroFlex Tower
Plant lettuce with space and feed evenly
- Into the tower from about 5 cm and with longer roots.
- Plant big plants first with spacing, small ones into the gaps.
- Top up with ready-mixed nutrient solution instead of changing every week.
- Without a permanent meter, measure every 2 to 3 days: first EC, then pH.
- The liquid nutrient stays until harvest, no bloom nutrient needed.
Air pump: It doesn’t go on the timer but runs constantly. If the leaves droop, the pump pause is too long.
What you need now: a HydroFlex Tower and Frankie’s liquid nutrient.
Detailed in the guide ›Step 4 · after about 4 to 6 weeks in the tower
Harvest from the outside, the centre keeps growing
- Use clean, sharp scissors.
- For loose-leaf lettuce harvest the outer leaves.
- Leave the heart in the centre.
- Pull out butterhead with the net pot, replant the spot.
- Wash leaves before eating.
Harvest in time: In heat or if it stands too long, lettuce bolts and turns bitter. Better harvest small amounts regularly and resow.
Detailed in the guide ›Step 5 · indoors under the lamp
Enough light, but no trapped heat
- Lamp at the side of the tower, 20 to 30 cm from the plants.
- Measure PPFD directly at leaf height.
- Fan on a gentle setting and not too close.
- Air the room for about 15 minutes every morning.
Too little light: Then the lettuce stretches and becomes long and thin. A full head of lettuce shows you the light is right.
Detailed in the guide ›1Germinating in the seedling box
about 3 days · no nutrient · cool and bright
I never start lettuce directly in the tower. The right germination temperature and the light are missing there, because hardly any light gets into the planting spots. That’s why mine germinates in the seedling box. The 25 cubes hang together there as a mat and keep each other moist.
Before first use I wash the mat hot to remove residues from manufacturing, then rinse it cold. Then it goes on a grid in the box. I fill in so much water that about a third of the mat stands in water. That way it soaks up from below without the seeds lying in water.
Lettuce needs light to germinate. You just put the seed in the slit of the cube and press it lightly. It isn’t covered. One seed per cube is enough, because each lettuce should later grow on its own. Only if your germination test turns out weak do you sow two seeds. If both germinate, cut off the weaker one directly above the cube.
Put the box under the grow light, 14 to 16 hours a day. So the surface doesn’t dry out, lay cling film over it or spray from above daily. No feeding yet, the seed brings everything it needs to germinate.
As soon as the seedlings are up, the film must come off, otherwise mould forms in the moist air. White fuzz on the root isn’t mould, by the way, those are root hairs. The fan stays off during germination, otherwise the cubes dry out.
What I use for this: my seedling box with 25 cubes and 10 lettuce seeds and for many plants the seedling mat with 100 cubes.
2Seedlings in the station
from the seed leaves · EC 0.4 to 0.8
When the little plants are about 2 cm tall and the first roots grow out of the bottom of the cube, they move. Lift the cube and look underneath. No roots yet? Then give them a few days. When transplanting always hold the cube, not the plant, and put it into a net pot of the seedling station. Those that haven’t germinated yet can keep germinating in the box.
At first the pot dips at most 0.5 cm into the water. Only when all plants have 2 to 3 cm of roots sticking out of the bottom of the pot do you lower the water level so that about 1 cm of air remains. Really check every plant, because one with short roots will otherwise dry out. The air pump runs in the station from the start, day and night, because the roots hang in still water here.
How I feed my lettuce
Once the seed leaves are open, the lettuce gets its first food. Young roots can’t handle much salt yet, so I start weak and increase in four stages as the plant grows. The millilitres only apply to my liquid nutrient. They’re a starting value, what counts is your meter.
| Stage | Frankie’s liquid nutrient | EC (mS/cm) |
|---|---|---|
| Germination | no nutrient | water only |
| seed leaves open | 0.5 ml per litre | 0.4 to 0.6 |
| young plant from 2 to 3 cm | 1 ml per litre | 0.6 to 0.8 |
| strong plant | 2 ml per litre | 1.0 to 1.3 |
| fully grown | up to 3 ml per litre | up to 1.6 |
In the seedling station I mix the nutrient solution fresh every 7 days. Measuring is easy: always set the EC first, then the pH. My nutrient lowers the pH, that’s why the pH measurement comes last. A green film on the cube is no reason to worry, by the way. Where it’s moist and bright, algae grow, and with the weekly change it stays harmless.
When the plants get bigger, I add a small fan. The gentle breeze makes the stems stronger and drives away the moist air between the leaves. On top of that I air the room for about 15 minutes every morning and keep the humidity below 60 percent. Otherwise mildew has an easy time.
What I use for this: my seedling station for 25 plants, net pots and Frankie’s liquid nutrient with dosing syringe.
Affordable, easy to use and perfectly adequate for beginners.
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3Move to the tower
from about 5 cm · EC 0.8 to 1.2
For me the seedling station is a kind of holding station. If the towers are still full, the young plants simply wait there. When I eat a lettuce from the tower, I refill the spot with the biggest plant from the station. From about 5 cm in size, when the roots are longer too, they can move.
Simply put the net pot into a free planting spot. I plant the bigger plants first, with enough spacing, the smaller ones go into the gaps. You don’t have to fill every spot, lettuce gets wide and needs air. The roots can hang out of the bottom, then they get water straight away with the next pumping. A support ring covers the pot, so no light reaches the cube and roots.
Pump timing
Indoors my pump runs for 5 minutes and then pauses for 30 minutes. That’s enough, the roots stay moist, and the plants also look for water themselves in between. If the tower stands outdoors in blazing sun, I switch to 15 minutes on and 15 minutes off. If the lettuce leaves droop, the pause is too long. The easiest way is a digital timer with a cycle function. The air pump doesn’t go on the timer, it runs constantly.
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HydroFlex Tower for indoors and outdoors, seedling box, seedling station, support rings and my own nutrient. After you buy, I’ll help you on WhatsApp.
To the shop ›4Growth in the tower
until harvest · EC 1.2 to 1.6
Lettuce stays in growth all its life, after all we harvest the leaves. That’s why I stay with my liquid nutrient until harvest, switching to bloom nutrient isn’t necessary. For fully grown lettuce, EC 1.6 is the maximum. My water has only EC 0.25, and my lettuces run at 1.1 to 1.2 and grow just as well. You don’t always have to take the maximum. If the leaves turn pale, add a little more nutrient.
Top up instead of changing
In a running tower I don’t change the water every week. I top up with ready-mixed nutrient solution that I mix in my 10 litre watering can. Then I measure: if the EC is too low, a little nutrient goes in, if it’s too high, plain tap water. Finally I check the pH, because fresh tap water raises it. If the EC rises for no reason or deficiency shows although pH and water temperature are right, I change the nutrient solution completely.
If you don’t have a permanent meter in the tank, measure every 2 to 3 days, always EC first, then pH. I lower the pH with a few drops of phosphoric acid. With my soft water, 2 to 3 drops per 10 litres are enough. Citric acid and vinegar don’t last, bacteria break them down and the pH rises again. More on my pages about the EC value and the pH value.
| Your water | EC without nutrient | What you do |
|---|---|---|
| soft | below 0.3 | feed normally, measure the pH more often at first |
| medium | 0.3 to 0.5 | feed by EC, a little less room is left for nutrient |
| hard | above 0.5 | mix half and half with rain or RO water |
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5Harvest
after about 4 to 6 weeks in the tower
Harvest loose-leaf lettuce from the outside in. The big outer leaves come off, the heart in the centre stays and keeps growing. Use clean, sharp scissors and rather harvest smaller amounts regularly. Pull out a butterhead lettuce with its net pot. Throw away the cube, clean the net pot, and a new young plant from the station goes in.
In heat or if it stands too long, lettuce bolts and turns bitter. A long flower stalk then grows up in the centre. It happens to me more often, because I simply grow more than I can eat. That’s why I prefer to resow small amounts regularly: if you want to eat lettuce roughly every day, about seven seeds per week are enough. That way you always have seedlings, young plants and ripe lettuces at the same time.
Light and location
Indoors you need a grow light. At the window the glass swallows light, it only comes from one side, and in winter the days are short. Lettuce needs about 200 to 300 PPFD, 100 to 150 is enough for seedlings. My lamps hang at the side of the tower, 20 to 30 cm from the plants, because from above the light hardly reaches the lower levels. With a strong lamp 14 hours are enough, with a weaker one leave it on for 16 hours, but never longer.
If light is missing, the lettuce stretches and becomes long and thin. A fully formed head of lettuce, on the other hand, shows me: the light is right. More on my page about lighting.
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Outdoors
Lettuce grows great outdoors, even in the rain. But rain dilutes the nutrient solution, so measure the EC afterwards. In the greenhouse it’s too warm for it, it bolts there. I put the tower outside from mid-May, because the water should be 18 to 22 °C. Lettuce tolerates cooler nights better than tomatoes or peppers. Get young plants raised under lamps used to the sun in the shade for a few days, otherwise they get sunburnt.
Pests on lettuce: what I look out for
Indoors you usually have little trouble with lettuce in the tower. Outdoors it’s different. You should know these four:
If your tower stands outdoors, put a fine insect net over it. That keeps aphids and other insects away from your lettuce. I use this net:
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Common problems and what helps
Brown leaf edges
Brown, dry edges on the young leaves are called tipburn. Almost always nothing is missing in the water. The calcium is there, it just doesn’t reach the edges of the young leaves. Calcium travels with the water flow the leaves create themselves through evaporation. Heat, very dry air but also still air slow this flow. Too high an EC and a lamp hanging too close can also burn the edges.
Indoors at my four towers my lettuce suddenly got brown edges. At first I thought the air was too humid. It was exactly the opposite: my fan was too close and dried out the edges, exactly on the side it was blowing at. I moved it further away and turned it to a gentle setting, hung the lamps higher and reduced the lighting from 16 to 14 hours. Brown edges don’t turn green again, but the new leaves grow back healthy.
Long, thin stems
That’s almost always too little light, usually on the windowsill in autumn and winter. The plant stretches towards the light. Such stems don’t get shorter again. The solution is a grow light right after germination.
Pale or yellow leaves
Measure the EC first. If it’s too low, add a little nutrient. Check the pH and water temperature too. If one of them is off, the plant can’t reach the nutrients even though they’re in the water. If the old, lower leaves turn evenly light green to yellow, nitrogen is usually missing.
Brown, slimy roots
Healthy roots are white or light and strong. If they turn brown, slimy and smell rotten, that’s root rot. Usually oxygen is missing because the water is too warm or stagnant. An air pump in the tank, a shady spot and a light-proof reservoir prevent it.
Aphids indoors
What was outdoors never comes into my house. Indoors I check regularly and dip small plants upside down with their net pot into a bucket of water. Then shake well and let them dry in the air. Keep at it, dipping once isn’t enough.
Fancy your own lettuce? View the HydroFlex Tower Classic 6+ →
FAQ about lettuce in hydroponics
Is lettuce suitable for hydroponics beginners?
Does lettuce need light or darkness to germinate?
At what temperature does lettuce germinate best?
How long does lettuce take to germinate?
How many lettuce seeds go into one cube?
Why isn’t my lettuce germinating?
When does lettuce move from the seedling box to the seedling station?
How high is the water in the seedling station?
When and how much nutrient does lettuce get?
What EC value does lettuce need?
What pH value does lettuce need?
Do I need to switch to a bloom nutrient for lettuce later?
When can lettuce go into the hydro tower?
How long should the pump run for lettuce?
How often do I change the nutrient solution in the tower?
How much light does lettuce need indoors?
Why does my lettuce get long, thin stems?
Why does my lettuce get brown leaf edges?
Why is my lettuce bitter or bolting?
How do I harvest loose-leaf and butterhead lettuce correctly?
When is the best time to harvest lettuce?
How much water does lettuce use in the tower?
Do I have to plant every opening in the tower?
You’ll find more vegetables without soil under vegetable growing in the hydro tower. You’ll find the right HydroFlex Tower for your space in my shop.
Continue with your own growing
168 pages, simply explained for beginners and with videos on the topics (in German). Exactly how I grow myself: from sowing to harvest.
More about the book ›A few questions about space, location and what you want to harvest, and you get a recommendation.
To the tower advisor ›Questions about your setup? Message me on WhatsApp.
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