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Seedling Leaves Turning Yellow – Is It Normal?

Whether planting one’s first garden seeds indoors when the outside weather is wintery or waiting to plant them outdoors when the temperatures have warmed up, planting seeds can feel entirely ceremonial to passionate gardeners. It’s a ritual that brings plant lovers great joy, a sign of new beginnings and future abundance.

As with most living beings, seedlings are fragile at the start of life and require more care than when they are mature plants. If seedling leaves begin to turn yellow, gardeners’ top concern becomes what can be causing this and how to resolve the issue.  

Seedlings require the perfect balance of light, moisture, soil, and nutrients to grow healthily. When gardeners experience their seedling leaves turning yellow, it could be a sign that one of these growth factors is off balance. Other possibilities for the cause of the discoloration of leaves could be drastic changes in temperature or pests. Whatever the cause, there are solutions to get your seedlings back on track.  

Read on to learn more about the causes and solutions to seedling leaves turning yellow.

Causes & Solutions of Seedling Leaves Turning Yellow

The following environmental stressors could all affect the health of seedlings, potentially causing their leaves to be yellow. The following sections share how to ensure seedlings are receiving enough of the elements they need to survive without overdoing it and damaging the plant.  

Light

Many gardeners use grow lights to start seedlings indoors from late winter through early spring. There are much smaller scale, affordable options on the market that make grow lights more accessible to at-home gardeners than what was available years ago.

When used appropriately, grow lights help to give indoor seedlings a healthy start with consistent levels of light leading up to the outdoor growing season. However, overuse of a grow light can be comparable to a scorching summer day and cause seedling leaves to turn yellow and wither. It’s essential to read the manual that comes with your grow light system and use the appropriate settings for seedlings.  

If seedlings are started outdoors, once temperatures have appropriately warmed, it’s essential to place them strategically to get enough sunlight to grow but not so much that they are getting sunburn.

Starting plants with exposure to morning and late afternoon light while slowly building them up to longer periods of more direct sunlight is ideal for healthy outdoor seedlings. This may require moving the plants around at first, depending on your garden setup and direction from the sun, but it is worth the effort as you watch your seedlings grow.  

Suppose seedling leaves are turning yellow and being overexposed to light. In that case, the best solution is to allow the seedling some shaded recovery time and immediately relocate the plants to a stably lit location.

If overly exposed to light, it is likely seedlings are also moisture deficient by the time they are displaying yellowing leaves. Giving seedlings a slow drink of water can help them get back to good health more quickly.  

Temperature

It is not uncommon to mistakenly have seedlings growing outdoors before temperatures are consistently warm enough. An overnight cold snap has surprised many gardeners and negatively affected seedlings. Seedlings prefer a steady warm temperature; extreme cold or heat will stall plant growth and affect leaf color.

Keeping seedlings outdoors early in the growing season is vital to monitor weather conditions daily and move seedlings indoors for drastic cold, increase shade for extreme heat, and shield them from harsh wind to maintain optimum plant health.    

If seedlings have been exposed to drastic winds or temperatures and are showing effects, including leaf yellowing, they should be moved to a calm environment with ideal temperatures of 65 – 75 degrees. Seedlings that have been exposed to extreme cold may show signs of recovery if moved to an indoor heating mat. Seedlings that have been exposed to extreme heat will benefit from shade and water.  

Moisture

Seedlings require more frequent watering but at lower quantities than mature plants. Seedlings need to live in containers with good drainage to help the moisture move through the soil and get absorbed by the plant’s roots with each watering. Maintain the soil by keeping it damp but not soggy, and never let it dry out. If the seedling is getting too much water or if the roots are thirsty, the first sign is often yellowing leaves. 

If a seedling’s leaves are starting to yellow due to too much or too little moisture, the most logical solution is to adapt the watering schedule. If one can’t tell visually if their seedling soil is lacking moisture or drowning the plant, a gentle press of the finger to the surface of the soil will easily answer that question.

Dry soil will feel hard to the touch and, just that, dry. Overly wet soil will feel soupy, and your gentle press of the finger will most likely plunge deeper into the soil than intended. The soil of perfectly hydrated seedlings will consistently feel like a cool-mist was sprayed over the plant, soil, and roots. Increasing or decreasing the watering of the seedlings to get to that cool mist feeling should also help to resolve yellowing leaves due to moisture.  

Soil & Nutrients

Starting seedlings in healthy, nutrient rich soil is ideal for healthy plant growth. There are a number of soil varieties at most garden centers that are specific to starting plants from seed and already have the necessary nutrients.

Look for seed starting soils that contain nitrogen, iron, potassium, and calcium for happy seedlings. If seedlings are grown in soil deficient in nutrients, the plant’s roots will become stressed, which could cause the seedling leaves to turn yellow.  

If your seedlings are showing signs of malnutrition, soil supplements can be purchased at most garden centers. Purchasing a soil kit can also be beneficial in assessing which specific nutrients your soil is lacking. Once the deficient nutrients are identified, purchasing and administering these supplements to your soil will help to resolve yellowing leaves and nurse seedlings back to health.  

Pests

Because seedlings are tiny, it is easy to catch medium to large pests that could affect the plant before they become a severe issue. However, some pests are so minuscule they can damage the seedling before the gardener sees them.

Spider Mites, Aphids, and Whiteflies are some of the most common pests that go easily unnoticed at first. Gardeners need to have an eagle eye to catch and mitigate these pests before they have too much impact on the plant. 

Pests are an annoyance and can damage seedlings quickly if not addressed. If you’ve identified pests on your seedlings, spraying a diluted mix of dish soap and water or neem oil and water can help kill and remove the unwanted pests from your plants.

Depending on the level of pest invasion you are experiencing, you will most likely need to apply one of these solvents daily until the pests are gone, and the plant is showing signs of recovery.  

Final Tips For Seedling Health

Seedlings are delicate and require more care than at any other stage of plant life. Keeping the balance of the factors discussed in this article will help you maintain healthy seedlings that turn into abundantly grown plants.

Knowing and following the planting guidance for each type of seedling, including planting depth and preferred temperatures, will also help keep your seedlings healthy. Lastly, applying a diluted liquid fertilizer every 2 – 3 weeks as the seedling grows into a stable plant will help maintain nutrients in the soil and regular absorption by the plant roots. Taking these combined steps of care will most ensure your seedlings are green, happy, and healthy.