When we start seeds indoors, we are trying to give them a head start before putting them into the harsh world of the out-of-doors. So, when our tender, baby seedlings seem to just pause, or stall in their growth, it can be very stressful.
Starting plants from seed is an exciting gardening activity. As gardeners we eagerly await those first seed leaves (cotyledons) breaking through the soil. However, sometimes seedling growth stalls after the cotyledons emerge. The plant seems stuck, with no second set of true leaves appearing. If your seedlings have stalled don’t panic. There are several common causes and solutions for this problem. In this article, we’ll explore the key reasons seedling growth may stall and how to get your plants back on track.
Why Seedlings Stall After Cotyledons
Here are the top causes of seedlings not progressing past their initial seed leaves
Lack of Proper Nutrition
Seeds contain all the nutrients required for seeds to germinate and grow their first leaves. But after that seedlings need additional food in the form of fertilizer to keep growing. If leaves are pale yellow and plant growth stalls after cotyledons emerge the seedling likely needs more nitrogen. Nitrogen is the nutrient critical for green, leafy growth.
Without adequate nitrogen, seedlings can’t produce the compounds needed to grow new stems and leaves. Deficiency shows up first in the oldest leaves as overall paleness or yellowing.
To fix this, give seedlings a diluted balanced fertilizer made for young plants. Look for “starter solution” or similar products. Apply according to label directions to thoroughly moisten the starting mix so roots take up nutrients.
Within a couple days, you should see renewed green color and growth. Continue regular feeding to prevent repeats.
Improper Lighting
Light is just as important as food for getting seedlings to progress past their initial leaves. Insufficient light triggers leggy, stretched out growth called etiolation. Seedlings elongate and strain upward seeking more light. They may get quite tall but have weak stems and no new leaf sets.
Outdoors, choose the sunniest window or location possible. Indoors, use grow lights positioned 2-4 inches above plants for 14-16 hours daily. Cool white fluorescent or LED plant bulbs work well.
If leggy seedlings are moved into better light, they typically resume normal compact growth. Burying extra-long stems up to the cotyledons when transplanting helps stabilize plants. But severely etiolated seedlings often remain spindly and weak.
Under or Overwatering
Too much or too little moisture prevents roots from properly taking up the nutrients critical for leaf growth. Underwatering shows up as wilting, drooping, and shriveled leaves. The starting mix will feel nearly dry. Water thoroughly until excess drains from the bottom.
Overwatering symptoms include yellowing leaves and leaf drop. Let containers dry out completely before watering moderately again. Ensure mixes and pots have excellent drainage. Let the top inch dry between waterings and use smaller containers. For seedling trays, let the reservoir drain fully.
Cool Temperatures
Like people, plants grow faster in moderately warm conditions. Most starting mixes provide bottom heat. But cool ambient temperatures slow growth.
Seedlings grow best with 65-75°F days and 60°F+ nights. Move flats or pots away from cold windows. Use heating mats, aquarium lights, or other gentle warming devices. Avoid irregular heat from appliances.
Monitor the temperature daily at seedling level using a thermometer. Maintain consistency for optimal growth. If location changes aren’t possible, consider starting plants later when indoor conditions are warmer.
Diseases or Pests
While less common on seedlings, problems like damping off disease or insects can sometimes stall growth. Damping off fungi quickly kill seedling stems at soil level. Thrips and other pests distort leaves and stunt growth.
To avoid disease, don’t overwater or crowd seedlings. Allow the starting mix surface to dry between irrigation. Disinfect trays and pots before reuse. Remove any diseased seedlings to prevent spreading.
Check leaf undersides for tiny insects, dots, or trails. Use a magnifying glass for close inspection. Appropriate organic pest control can remedy mild infestations. Heavily affected plants may need discarding.
Getting Stalled Seedlings Back on Track
With some troubleshooting and TLC, many struggling seedlings resume normal growth. Follow these tips based on the seedling’s size:
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For seedlings with true leaves, transplant into potting mix containing compost or fertilizer. The added nutrients get them growing again.
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For seedlings with only cotyledons, add diluted starter fertilizer to the starting mix. This provides missing nutrition without disturbing tiny roots.
Monitor plants and watch for renewed growth after taking corrective actions. Seedling stall can be frustrating but is often fixable. Have extra seeds handy to account for unavoidable losses. Check seedlings daily and be ready to intervene with light, warmth, nutrients or moisture to get growth back on track.
What does “seedling stall” look like?
Seed stall is when a seedling that spouted stops producing new growth. With tomatoes, for instance, it can look like the tomato sprouted it’s seed leaves (the first two leaves) and then nothing happens after that for at least a week. It can also happen later, after some true leaves have sprouted, and then the plant just seems frozen in time. Alive, but “stuck” at that same stage. Sometimes you will also see signs of a nutrient deficiency like purple or yellow discoloration of the leaves or stem.
How do I know I’ve fixed the problem?
Once the seedlings have access to the right nutrition, they should start growing again. You should see new growth, and any discoloration should fade. Taking pictures daily will help you to see this process as it occurs, since you might not notice changes just by checking every day. Tomato seedlings showing new growth beyond the seed leaves. Now it’s time to thin them out!
7 Solutions For Stunted Seedlings
FAQ
Why is my plant not growing new leaves?
How many sets of true leaves before transplanting?
When weather conditions are appropriate and your seedlings have at least 2 true leaves, it is time to transplant them to your garden outside!
How do you encourage leaf growth?
Humidity and Fertiliser for Bigger Leaves
Fertilisation is another key element in promoting healthy, vigorous growth. Applying a balanced liquid fertiliser every four to six weeks during the growing season (spring and summer) provides essential nutrients that support larger leaf development and strong roots.
What is the second set of leaves called?
True leaves are the second set of leaves to grow, and they resemble the mature plant’s leaf shape on a smaller scale. Unlike cotyledons, which feed themselves from the seed’s stored energy, true leaves perform photosynthesis to start supplying the plant with food for its next growth stage.
Do true leaves come after seed leaves?
True leaves come after seed leaves. Whereas there will only be one set of seed leaves throughout the plant’s life, new true leaves will grow for as long as the plant is growing. The first few sets of true leaves will be the same shape as the adult foliage, just baby-sized. As the plant grows, it will put out larger leaves.
How long after germination do true leaves appear?
Usually, true leaves will appear one to three weeks after germination. This time will vary based on the kind of plant and the growing conditions, including light and water. True leaves are normally measured in “sets.” So if you have “one set of true leaves,” that’s two leaves. How do you know if a seedling has true leaves?
When should I thin my seedlings?
When your seedlings develop their first true set of leaves, not the first or two little mouse-ear shaped cotyledons that develop right after the seed germinates but the true leaflet set of leaves, it’s time to thin your seedlings. Save my name, email, and website in this browser for the next time I comment.
Can You transplant a seedling if it has two leaves?
Transplanting a seedling before it has two true leaves can cause the plant to have stunted growth. Before transplanting, gently lift the seedling out of its container, and check its root growth. Don’t transplant the seedling if its roots are very small.
How do you tell if a seedling has true leaves?
True leaves have the appearance that all future leaves on the seedling will have, and they probably look very different than the first leaf or two that you see. (See pics below for examples of the 1st and second set of leaves.) Take a pair of scissors and cut the weakest seedlings off at the soil line. When should I thin my seedlings?
What happens if seedlings don’t get enough nitrogen?
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.