Problems With Your Seedlings?

Even when following a detailed guide on growing seedlings indoors, it is normal to encounter a few pitfalls. For novice gardeners, these difficulties can be discouraging, especially when the real causes of the problems are poorly understood or when similar symptoms hide different causes. Fortunately, there is a solution to every problem. You just need to learn to spot the signs, understand the underlying causes and apply good practices. Here is a list of common problems encountered with indoor seedlings, along with practical solutions that are easy to implement.

Uneven Germination

Uneven germination, where some seedlings grow quickly while others do not germinate at all, is often due to poor quality or seeds that are too old, inadequate depth or unsuitable germination conditions (temperature, humidity). To avoid this, use fresh seeds and follow the specific instructions for each variety, including sowing depth and optimal temperatures. You can also carry out a germination test to check their viability before planting them, especially with older seeds. Store your seeds in a cool, dry place to preserve their viability.

Don’t forget that some seeds require stratification (exposure to cold) or scarification (abrasion of the shell) to germinate.

Damping Off

Damping-off is a fungal disease that causes young plants to collapse at ground level, often accompanied by a slimy or pasty area at the base of the stem. This problem mainly occurs in conditions of excessive humidity. The pathogens responsible often include the fungi Pythium, Fusarium and Rhizoctonia. To prevent it, use sterile soil and clean containers and ensure good drainage. Before sowing, clean the pots and trays with a soapy water solution or a dilute bleach solution (10%) to eliminate residual fungal spores or pathogens. Avoid over-watering and ensure good air circulation by using a fan if necessary. Maintain humidity at around 50-60% and a stable temperature between 20 and 25°C (68 and 77?) to reduce the risk of fungus growth.

Poor Quality of the Substrate

Unsuitable or old potting mix can make the soil compact and poorly suited to water retention, which slows down the growth of seedlings. Signs of old potting mix include a musty smell, a very compact texture or an inability to retain moisture. Choose a quality, light and fresh potting mix specially formulated for seedlings or for repotting potted plants. If necessary, add perlite or vermiculite to improve the structure and promote good drainage. Note that an excess of unripe or poorly balanced compost can disrupt the humidity and cause seedlings to wilt.

Slow Growth

Seedlings may appear to stagnate or show slow growth when temperatures are too low, nutrients are insufficient or the soil is compacted. Inadequate watering, whether excessive or insufficient, can also slow down their growth. Ensure that growing conditions are appropriate by maintaining optimal temperatures (generally around 20 to 24°C, 68 to 75?, during the day and 16 to 20°C, 60 to 68?, at night, to be checked according to the species). The use of a thermometer or a heating mat can help maintain a stable temperature, especially in colder environments. Fertilize very lightly with a diluted organic fertilizer suitable for seedlings, starting with 1/4 of the recommended dose to avoid any risk of burning. Gradually increase to 1/2 of the dose if the seedlings show good tolerance.

Leggy Seedlings

Seedlings with abnormally long and weak stems are caused by a lack of light. Provide 14 to 16 hours of bright light per day using full-spectrum LED lamps or fluorescent tubes. Place fluorescent lamps 10 to 15 cm (4 to 6″) away and LED lamps 20 to 30 cm (8-12″) above the seedlings to avoid overheating and ensure adequate lighting. If you use natural light, place the seedlings near a south-facing window or use reflectors to maximize the lighting.

Purple Leaves

If the seedlings have purple leaves or stems, this may be due to a phosphorus deficiency, often caused by cold temperatures that reduce nutrient absorption. To correct this problem, warm the soil slightly, ideally with a heating mat. If this does not work, apply a phosphorus-rich fertilizer. Also check that the pH of the soil is between 6 and 7 for optimal absorption of nutrients, which is generally ensured with a quality commercial potting soil. Sometimes, this coloration can be a genetic trait specific to the variety, and in this case, no intervention is necessary.

Anthocyanins, natural pigments belonging to the flavonoid family, are probably responsible for the purple coloration of your seedlings. Their production is influenced by various environmental factors and can be triggered in reaction to water stress, excessive heat or cold. These pigments play a protective role by helping plants adapt to difficult conditions.

Leaf Discoloration

Yellowing leaves, particularly on the oldest leaves or the tips, are often caused by too much or too little water, or a lack of nutrients such as nitrogen. Poorly drained soil can also aggravate this problem by asphyxiating the roots. Maintain constant moisture and ensure good drainage of the soil to avoid the accumulation of standing water. Apply a mild fertilizer, ideally rich in nitrogen, when the seedlings have 4 to 6 true leaves to promote healthy growth.

Wilting of the Leaves

Leaves that fall and lose their rigidity are generally a sign of damaged roots in soil that is too dry or too wet. Poor-quality soil or an excess of mineral salts can also damage the roots. Adjust your watering practices, making sure that the soil remains evenly moist, but never soggy. If necessary, repot the seedlings in fresh, well-drained soil, and make sure not to use water that is too rich in minerals for watering.

Root Circling or Constriction

When roots become entangled in a pot that is too small, it limits their ability to absorb water and nutrients. Signs that the roots are cramped include slowed growth, visible roots coming out of the drainage holes or the soil drying out quickly after watering. Repot your seedlings quickly in larger containers as soon as these signs appear, in order to promote optimal root development and healthy growth.

Mold or Fungus on the Soil

White, green or black mold on potting soil is brought on by excessive humidity and poor air circulation. Reduce watering, improve ventilation with a fan and make sure that the seedlings are not too close together, which allows for better aeration. If the problem persists, consider replacing the affected soil with a new substrate to avoid reinfection.

Parasite Infestations

Pests such as aphids can attack seedlings and cause visible damage to the leaves. Early signs of infestation include sticky leaves, yellowish spots or localized discoloration. A gentle spray of water or the application of insecticidal soap (test on a leaf before widespread application) may be enough to eliminate them. For a natural approach, introduce beneficial predators. Place infested plants in quarantine to prevent the spread of parasites.

Soil gnats (sciarids) are also a common nuisance in damp seedlings. To limit them, allow the surface of the substrate to dry slightly and use yellow sticky traps.

Leaf Spots

Irregular or circular spots on the leaves, sometimes accompanied by holes, often indicate a fungal or bacterial infection. Remove the affected leaves, avoid wetting the foliage when watering and improve air circulation to prevent the problem from recurring.

Fertilizer Burn

When the tips and edges of the leaves turn brown or black, it may be caused by over-fertilization. Rinse the soil with clean water to remove excess fertilizer and reduce the doses during future applications. To prevent this problem, use organic or slow-release fertilizers, and only fertilize when the seedlings show signs of active growth. Also be sure to check the recommended dosages on the fertilizer packaging. As seedlings have low fertilization needs, you can dilute the fertilizer to 1/4 or 1/2 of the recommended dose to avoid stress.

Thermal Stress

Temperatures that are too high or too low can cause heat stress, slowing growth and damaging the leaves. Use a heating mat to maintain optimal temperatures in cold conditions. In case of excessive heat, improve air circulation with fans or install a shade sail to protect the seedlings from direct sunlight, if necessary. Also make sure to maintain adequate humidity, as excessively dry air can accentuate the effects of heat stress.

Overheating of Seedlings Under a Dome

A germination dome creates a greenhouse effect, trapping heat and humidity to encourage the seeds to germinate. However, it must be removed as soon as the seedlings appear, as the temperature inside the dome rises rapidly, especially under intense light such as sunlight, which can cause overheating and weaken the young shoots. In addition, excessive humidity encourages the seedlings to melt and mold to proliferate. To avoid these problems, remove the dome as soon as the first seedlings emerge or move the seedlings out of the dome.

The majority of seeds do not need light to germinate. It is the humidity and the temperature that trigger the emergence. Placing a seed tray with a dome in direct sunlight before germination is pointless and risky, as the greenhouse effect under the dome can damage the young seedlings. It is best to keep them in a warm place, but out of direct sunlight, and then place them under suitable lighting once they have germinated.

Excessive Light

Prolonged exposure to intense light, whether natural or artificial, can cause burns or whitening of the leaves. Adjust the distance of the lamps above the seedlings to avoid overheating. Gradually accustom seedlings to sunlight by increasing their exposure in stages over several days.

Prolonged exposure to excessive light, especially with very powerful LED lamps placed too close, can cause a defensive reaction in plants. This can lead to an increase in the production of anthocyanins, the pigments responsible for the purple or mauve hues on leaves and stems.

Exhaustion Due to Late Repotting

Seedlings can become weak and stressed if repotting is delayed too long. Repot them as soon as they have 2 to 4 true leaves to prevent them from suffering from limited space or exhaustion due to lack of nutrients. Handle the roots gently to minimize stress, and replant them in well-drained, slightly enriched soil to help them adapt. Water moderately after transplanting to help the seedlings recover quickly.

Of course, if you use larger containers from the start (like me), this step can be avoided.

Good Habits

To succeed in sowing without too much effort, adopt a few simple habits. Use good quality, fresh, light, well-drained soil, keep it slightly moist and ensure that your young shoots get enough light. Maintain a comfortable temperature and give them a little nutrition at the right time. Transplant your seedlings as soon as they show that they lack space to grow and ensure good ventilation. Finally, observe your plants regularly to detect any problems before they become unmanageable. With these tips, your seedlings will be in great shape and ready to move on to the next stage without you having to worry too much!

By applying these few principles and integrating solutions tailored to your needs, you will maximize your chances of success and get seedlings in top shape, ready to face the next stage of their growth!

Do you have any other problems with your seedlings? Write to us in the comments so that we can add the solutions to the text and help other gardeners.