Troubleshooting When the Second Set of Leaves Doesn’t Grow on Seedlings

It’s an exciting time when you first see those tiny seed leaves (cotyledons) emerge from seed starting mix But then the waiting game begins for the seedling’s first true leaves Sometimes that second set of leaves seems to take forever to appear, or doesn’t show up at all. What gives?

There are a few key reasons why seedlings sometimes stall out after the cotyledons emerge:

Lack of Proper Nutrition

Seeds contain all the nutrients they need to germinate and grow their first pair of leaves. But after that, seedlings need food in the form of fertilizer to keep the growth process moving. When a plant appears to have stopped growing for several days and the leaves are pale or yellowing, it likely needs more nitrogen. Nitrogen is the critical nutrient for healthy green vegetative growth.

Without adequate nitrogen, seedlings can’t produce the proteins and enzymes necessary to grow new leaves and stems Deficiency shows up first in the oldest leaves, causing them to turn uniformly pale or yellow

To fix it, give seedlings a dilute solution of balanced fertilizer designed for young plants. Look for options marketed as “starter solution” or similar. Apply according to label directions. Thoroughly moisten the starting mix to ensure roots take up nutrients.

Within a couple of days, you should see renewed green color and growth. Continue fertilizing on a regular basis to prevent repeats of the issue.

Improper Lighting

Light is just as crucial as food when it comes to getting seedlings to progress beyond their initial leaves. When light is insufficient, it triggers a classic issue called etiolation or legginess. Seedlings stretch and strain upwards looking for more light. They can grow quite tall, but with weak stems and no new leaf sets.

Outdoors, find the sunniest window or location possible. Indoors, use grow lights and keep them as close as possible without overheating plants. Cool white fluorescent tubes or LED plant bulbs work well. Position lights 2 to 4 inches above transplants and operate 14-16 hours per day.

If leggy seedlings are moved into better light, they will usually resume normal compact growth. Burying extra-long stems right up to the cotyledons when transplanting helps stabilize plants. But severely etiolated transplants often remain spindly and weak.

Under or Overwatering

Too much or too little moisture prevents roots from properly absorbing nutrients critical for leaf growth. Underwatering causes obvious symptoms like wilting, drooping, and shriveled leaves. The starting mix will feel nearly dry when you stick your finger in to check beneath the surface. Water thoroughly until you see excess drain from the bottom.

Overwatering is trickier to recognize. The mix may still feel damp or look dark. Seedling leaves often yellow or drop off when kept too wet. Let containers dry out for a few days before watering moderately again.

Ensure starter mixes and containers have excellent drainage. Allow the top inch to dry between waterings. Use smaller pots to avoid staying wet too long. For seedlings started in flats or trays, let the bottom reservoir drain fully so roots don’t sit in water.

Cool Temperatures

Just like people, plants grow faster when temperatures are moderately warm. Most seed starting mixes are formulated to provide warmth from below. But cool ambient air can slow growth to a crawl.

Seedlings grow best with daytime temperatures of 65-75°F and nights no cooler than 60°F. Move flats or pots away from cold window glass. Place them atop heating mats or near other gently warming equipment like aquarium lights. Avoid hot irregular heating from appliances.

Monitor the temperature daily at seedling level. Use a thermometer to check if unsure. Maintain consistency for optimal growth. If location changes are not feasible, consider starting plants later when indoor conditions are naturally warmer.

Diseases or Pests

While less common on seedlings, problems like damping off disease or insect pests can sometimes be the culprit. Damping off fungi quickly collapse and kill stems at soil level. Thrips and other insects can distort leaves and stunt growth.

To avoid disease, don’t overwater or crowd seedlings. Allow the starting mix surface to dry between waterings. Disinfect flats and trays before each use. Remove any seedlings that show signs of disease to prevent spreading.

Check for pests on undersides of leaves. Look for tiny insects, white dots, or silvery trails. Use a magnifying glass to inspect closely. Appropriate organic pest control measures can remedy mild infestations. Severely affected plants may need to be discarded.

With a little troubleshooting and TLC, most struggling seedlings can get back on track and start developing their first true leaves. But some may never recover from an early setback. Having extras on hand helps account for unavoidable losses. Monitor seedlings daily and be ready to intervene with light, warmth, nutrients or moisture to prevent stalled growth.