Petunia Seedlings Not Growing? How To Fix It

Petunias are easy to grow and propagate, which makes them a popular flower with gardeners. However, despite their popularity, petunias are not immune to problems. In particular, many gardeners have reported issues growing petunias from seedlings. 

If your petunia seedlings aren’t growing, there’s a chance they aren’t getting the adequate light, water, or soil pH that they need to grow. It’s also possible that none of the seedlins germinated properly when planted. You should also be on the lookout for disease and pests. 

In the rest of this article, I’ll discuss the factors that affect your petunia growth and how to troubleshoot these common issues. Then, we’ll go down the list of ways to fix your petunia seedling issue. 

Factors That Affect Petunia Seedling Growth 

With all plants, I like to troubleshoot my problems the same way. If there is a visual problem that might be the cause of the plant’s woes at hand, I start there. Otherwise, I ask myself the following:

  • Am I underwatering or overwatering?
  • Am I giving these plants adequate sunlight?
  • Is the temperature and season for growing right?
  • Do these plants look sickly, like they may have a disease?
  • Do I see any pests or have suspicions about pests?
  • Is my soil pH off?
  • Am I giving these plants nutrients through the soil?

For petunias, I commonly see underwatering/overwatering, temperature, and/or sunlight issues in the garden, especially in the early stages of growth. Seedlings should germinate and begin to sprout within 30 days, and they usually flower around a month after that. 

If you can’t get past the pre-sowing or transplanting stage, something is wrong with your petunia’s basic needs.

Sunlight for a Petunia

Petunias need at least six hours of direct sunlight each day. If your seedlings aren’t getting enough sunlight, they probably aren’t growing because they aren’t photosynthesizing as they need to be.

If your plants get enough sun but are exposed to massive amounts of heat, this can also affect growth. Petunias love cool weather, so if your seedlings get too much heat, they won’t grow well. 

You have to find a balance between the right amount of sunshine and the right amount of heat. Temperatures shouldn’t exceed 65 °F (18.33 °C). The perfect balance may require leaving your petunias in the sun for the morning, when it’s cooler, and then giving them some shade. In this way, as I’ll talk about more below, the balance is necessary.

Watering Petunias 

Watering issues are one of the most common reasons your petunias are not growing. 

For petunias, the soil needs to be kept moist at all times. They love the sun, but too much sunshine or heat can dry out the soil, leaving your petunia thirsty. Too much sunshine may also burn the roots or stems of your plant if it isn’t watered regularly enough.

This means that to mitigate any sun issues (besides solving the sun issues themselves), you must ensure your plant dirt is always moist. 

However, don’t overwater, either! Overwatering soil can drown out the roots and cause soil compaction, which makes it nearly impossible for microorganisms to live and support your soil. Again, you’ll need to find the perfect balance of watering without overwatering.

Watering petunias in pots is different from watering petunias that grow in the ground. To learn more about watering petunias in pots, you can ready my other article: How Often Should You Water Petunias in Pots?

Common Petunia Illness and Pests 

All plants are susceptible to illness, but petunias have a few issues they are commonly plagued with. A few of these include:

  • Botrytis Blight
  • Thrips
  • Crown Rot
  • Stunting
  • Viruses

Some of these things originate in outside factors out of your control, while others are due to nutrient deficiencies. While you can’t control what diseases are spreading around the garden, you can ensure your soil is healthy enough to deter pests and that your plants are healthy enough to fight off any infection.

Fighting off infection, even in the healthiest seedling, will be difficult. Pay extra attention to signs of illness if your seedlings just won’t grow. 

How To Fix Petunia Seedling Growth 

To fix your petunia seedling growth problems, I’d highly suggest using one or more of the following methods in tandem. Of course, as discussed above, look for obvious signs of what may be causing the problem before proceeding with everything. It may be a disease if you see any weird spots on the sprouted leaves. If it seems like your soil is compacted, you’re overwatering

Check for obvious signs of an issue and mitigate them before working through this list. While all these methods will improve your garden, it’ll waste precious time to do everything without considering the root cause of seedling stunting. 

1. Re-Work Your Implantation Method

Petunia seeds are germinated in spring and transplanted when they reach a height of 12-15 cm or 4-5 inches. If you’ve planted them in the ground, you still need to be intentional about where you’re setting your seeds. If you’re moving them before then, you may not be giving them enough time to grow in their original spot. This is, of course, only relevant for container gardeners.

Overcrowding is another reason why your petunia may not be growing. When you plant more than one seedling in the same pot, they will compete for nutrients and sunlight. 

This will result in your plants being stunted, and you may not get as much growth from each plant as you would like. When you plant your petunias, space them apart, so each plant has enough room for growth. 4-6 inches (10.16-15.24 cm) is usually an okay amount of space between petunias. 

2. Confirm Their Basic Needs Are Being Met

It goes without saying, but I’ll say it anyway: all plants are different and require different conditions!

You can’t treat your petunias like your tomatoes and vice versa. For petunias, in particular, make sure you’re giving your petunia garden:

Before planting, it’s also important to prepare the soil by adding compost or peat moss. This can add nutrients to your otherwise nutrient-deprived soil. 

Additionally, the soil should be well drained and slightly acidic (with a pH of around 6). 

The pH of your soil is a measure of its acidity or alkalinity. It’s a scale from 0 to 14, with 7 being neutral. 

A petunia grows best in soil with a pH level between 6.0-7.0, so ensure you have the right conditions for it to thrive! If needed, you can adjust your soil by adding sulfur or lime to lower the pH. 

3.  Troubleshoot Pests and Diseases

Pay attention to things that may be harming your plants. If you see any bugs, like aphids or whiteflies, kill them by gently shaking the plant from side to side over a plate of soapy water (about 1 tablespoon of dish soap per cup of water). Use a magnifying glass to make sure you don’t miss anything! I also swear by gently rubbing neem oil onto my petunias.

For what has grown or the surrounding plants, check for anything that’s off. If you notice that leaves are yellowing, turning brown or molding, you may have a disease outbreak in the garden.

4. Invest in a 5-Program Moisture Meter

It can be difficult and time-consuming to decide whether or not your plants are getting enough water. Luckily, there is a solution: invest in a moisture meter

Moisture meters are fairly inexpensive and easy-to-use devices that make it simple to check the moisture level in your soil on any given day. For petunias, in particular, a moisture meter will save you the guesswork of whether your plants are over, under, or perfectly watered. 

That way, no matter how busy your schedule gets or how many other tasks are vying for your attention, you’ll know exactly when it’s time for another watering session—and how much water each plant needs.

5. Select a Different Spot in Your Garden

Sunlight is a huge growth factor. Petunias need lots of sunlight, so choose an area that gets plenty of light throughout the day but is not exposed directly to midday sun. Direct exposure will cause scorching on leaves, resulting in reduced flowering and stunted growth

Six hours of indirect natural sunlight is the sweet spot, and ensure your petunias get this much sun each possible. If possible (and necessary), pick up your petunia pots and move them around the house to ensure they’re not directly in the sun. if you missed the growing season, or your seedlings cannot be saved, remember this next year with your next batch of pentunias!


Gardening requires patience, and everything blooms in its own time. As long as you see sprouting results that seem typical and you’re doing everything you should be for your petunias, they may surprise you and eventually pop up! You can use these tips to ensure your petunias are growing properly and you are getting the best possible results.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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