When and How to Fertilize Lettuce Seedlings and Other Leafy Greens
You planted your seeds with care, and they germinated. (Yay!) Now you’re wondering: Do I need to fertilize my lettuce seedlings? And if I do, when and how should I do it?
Let’s take a look at the basics of seed-starting and how to give your seedlings what they need at the right time, including fertilizer.
Seedling Stage
Before you even think about introducing nutrient solutions, it's important to understand the seedling stage of lettuce plants. Seedlings are typically the stage after germination, when the plant is still delicate and establishing its root system. During this phase, lettuce seedlings primarily rely on the nutrients stored in the seed itself for growth.
Cotyledons Development
The first true leaves of lettuce, known as cotyledons, are an indicator of when to start feeding nutrient solutions. Cotyledons are the initial source of energy and nutrients for the seedling, and they typically sustain the plant for the first week after germination.
When the cotyledons start to yellow or wither, it's a sign that the seedling has exhausted its internal nutrient reserves and is ready for external nourishment.
A good rule of thumb is to wait until the seedling grows its second set of true leaves to start fertilizing. True leaves are the actual foliage of the plant. They look and function the same way that all future leaves will.
Root Growth
Another critical factor to consider is the development of the root system. In hydroponics, the root system plays a vital role in absorbing nutrients from the solution. Before introducing nutrient solutions, ensure that the lettuce seedlings have established a sufficient root system. A healthy root system should have several well-developed roots that can easily reach the nutrient-rich solution.
Nutrient Solution Strength
When you do decide to introduce the nutrient solution, it's essential to use a solution with the appropriate strength. Seedlings are delicate and can be sensitive to high concentrations of nutrients.
Start with a diluted solution on half strength around 300 ppm, gradually increasing the strength as the seedlings mature. Refer to Nutrihydro's nutrient mixing calculator for your needed efficiency.
pH and EC Monitoring
Maintaining the right pH and electrical conductivity (EC) levels in your nutrient solution is crucial for the health of your lettuce seedlings. Lettuce typically thrives in a slightly acidic pH range of 5.5 to 6.5. The EC level indicates the concentration of nutrients in the solution. Regularly monitor and adjust both pH and EC to ensure the ideal growing conditions.
Temperature and Light
Lastly, don't forget about environmental factors. Temperature and light play significant roles in the growth of lettuce seedlings. Ensure that your hydroponic setup provides the appropriate temperature and light levels for your specific lettuce variety.
In conclusion, knowing when to introduce nutrient solution to lettuce seedlings in hydroponics is a crucial aspect of successful cultivation. Waiting until the cotyledons begin to wither and the roots are well-developed is generally a safe approach.
Remember to start with a diluted nutrient solution, monitor pH and EC levels, and provide the right environmental conditions for your lettuce seedlings to thrive. With proper care and attention, you can enjoy a bountiful harvest of healthy, nutrient-rich lettuce from your hydroponic garden.
Seed-Starting Troubleshooting
Here are some things that can go wrong when starting seeds:
Thin, leggy seedlings with yellowing leaves
Cause: Not enough light. Seedlings need very bright light to thrive. Even the light from a sunny windowsill is not enough for seedlings. When starting seeds indoors use fluorescent or LED tube lights that can be adjusted up and down.
Seeds not germinating
Cause 1: Grow medium temperature is too dry, too warm or not warm enough. Always check the soil temperature to meet the requirements of the particular plant/crop. Here is a good reference for soil temperatures: Soil Temperature Conditions for Vegetable Seed Germination.
Cause 2: Seed was planted too deep. Check the seed packet to see what the optimum seed depth should be. Seeds planted too deeply will have delayed germination or completely fail to germinate.
Sudden seedling death
Cause: When seedlings suddenly die, the most common cause is a disease known as “damping off”. This is typically caused by cool, moist conditions. Prevent damping off by always bottom-watering seedlings. This is why it’s important to use a high-quality, three-part seed starting tray system with a bottom tray (no holes), cell tray, and plastic humidity dome.
To bottom-water seedlings, fill the bottom tray with enough water so that the plants absorb it all within 24 hours. Never let water sit in the bottom tray. Only water again when the bottom tray is completely dry, and the cell tray starts to feel lighter in weight.
Go start some seeds!
Now that you’re armed with everything you need to know to get your seedlings off to strong start, it’s time to go start some more seeds!
When you grow hydroponically, you are in control of the growing environment so you can garden in all seasons. To maximize your garden’s productivity, make sure that you are starting seeds regularly, not just once a year.
Happy gardening!
