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Petunia Seedlings Not Growing – What To Do?

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Petunias may be reliable annuals, but they are sensitive as seedlings. During their early stage, the seedlings could suddenly stop growing. If you are wondering why this happens and want to know what to do, you landed on the right page. We know the reasons behind this and have researched as well what you can do so they would continue to thrive and bloom. 

When petunia seedlings are not growing, it could be due to inappropriate temperature, poor soil quality, or excessive watering. Sometimes, planting the seeds too deep also slows down their development. Here's what you can do when petunia seedlings are not growing.

  1. Use fertile soil or seed starting mix.
  2. Do not overwater.
  3. Ensure ideal temperatures for petunia seedlings.
  4. Do not plant the seeds too deep. 

Petunias can be challenging to grow when you are unfamiliar with their needs, but we're here to give you all the information you need. Read through our post to know how to plant petunias properly and how to make them grow faster.

Replanting plants onto plastic pots on a table, Petunia Seedlings Not Growing - What To Do?

Petunia Seedlings Not Growing - What To Do?

Petunias are generally easy to grow under ideal conditions. Otherwise, the seedlings may develop slowly. In some cases, the seeds rot even before they begin to germinate. So what can you do to avoid petunia seedlings that are not growing?

Dazzling colors of petunia flowers at a small garden

Use fertile soil or seed starting mix.

Growing any kind of seeds starts with good soil. Petunia seeds will develop faster on healthy, fertilized soil. The ideal soil for these flowering annuals should be moist but drains very well. It is not recommended to reuse soil as well. Instead, you can buy seed starting mix or make your own. 

To make a seed starting soil from scratch, combine two parts each of compost and peat moss, and add only one part of vermiculite. Compost provides nutrients for the seedlings and has the ability to hold water well. Peat moss gives lasting moisture as it decomposes slowly, whereas vermiculite holds air that helps fluff up the soil mix.

Small growing petunia plants growing at the garden

Compact and dry soil does not make a good environment for petunia seedlings. At the same time, watch out for bad odor, moss growth, and insects which are common signs of poor soil quality.

Do not overwater.

Petunia seedlings need damp soil to grow fast, but it does no good when you overwater. When the soil is too wet, the seeds may not even begin to develop but rot. On the other hand, petunia seedlings in an overwatered environment may show symptoms such as the presence of white spots on leaves and yellowing leaves. When left in the same situation for extended periods, the seedlings will damage their roots.

Underwatering the seedlings is as bad. You would notice the same symptoms when the seedlings do not get enough water. Their growth slows down, and they are likely to die soon.

Full bloom petunias need watering once every 7-10 days, but damp soil is a primary requirement for seedlings until they have established their roots. As a guide, make sure to keep the 6-8 inches of topsoil moist until the seedlings have grown their roots.

Maintain ideal temperatures for petunia seedlings.

Petunias love sunlight, but the case is different for seedlings. Direct exposure to sunlight for long periods is a lot for the seedlings to handle and is probably the reason why they are not growing. Soon enough, they will wilt and die.

It is best to plant petunia seeds indoors, and they remain in the indoor environment for a few weeks after germination. The ideal environment should have a temperature ranging between 75 degrees and 80 degrees Fahrenheit.

But because the seedlings need warmth and light during the early stages, you should place your seedlings under a fluorescent light. The gap between the light source and the seedlings should not be more than 6 inches. As well, check that the temperature is between 60 and 65 degrees Fahrenheit and kept on for 12 to 16 hours.

Keep your seedlings under the same condition until they have established at least three leaves. If a fluorescent light source is not available, you can place your petunia seedlings near the window.

Do not plant the seeds too deep.

You may have planted the seeds too deep, which is probably why you think the seedlings are not growing. Needless to say, it takes the seedlings longer to reach the topsoil during the germination period when they are planted too deep.

Petunia seeds are very tiny. There could be around 300,000 seeds in a single ounce. This extremely small size makes it a challenge to plant petunias which is why they are now being coated into pellets to improve their size. Pelleted or not, you should not plant the seeds deeper than 1/4 inch.

Now that you know the basic needs of petunia seedlings, you should easily be able to identify what causes their slow development. Correct the case to save the seedlings, but if impossible, you can grow petunias from seeds again. We will also show you how to make them grow faster.

How to Make Petunia Seedlings Grow Faster

Gorgeous blooming petunia flowers photographed at the garden

Regardless of the variety, the most delicate stage of the petunia life cycle happens during the sowing and germination phases. Proper temperature, healthy soil, and enough moisture are all crucial when you start these annuals from seeds.

When you meet all of these conditions, in addition to proper care and handling, the seeds should begin to germinate in just 7 to 10 days. So how do you plant petunia seeds and make sure they germinate right in time and grow to full bloom without problems?

Plant during the frost-free seasons.

You should plant your petunia seeds at least 10 weeks before the transfer day. However, avoid planting the petunias when the frost danger is approaching. If you are in the northern location, March would be the most ideal time to start planting, and a little earlier when you live in the southern area.

Begin with indoor planting.

While petunias love to be under the sun, it is best to start from seeds indoors. The seedlings have lower chances of making it through full bloom when they are receiving more sunlight than they can handle.

Use clean planting trays.

Gardener placing soil on small pink containers on planting tray

To plant petunia seeds, it is important to use clean planting containers to avoid bacterial and fungal contamination. While your plant may not wilt from too much sunlight or lack of moisture, these contaminants could be the culprit that they die prematurely. 

Make holes around the planting trays for drainage.

A seed starting mix may be known to have properties that drain well, but it would be risky to plant petunia seeds in a container that does not have proper drainage. Use planting containers with holes at the bottom or improvise and punch holes to allow excess water to drain out of the mix.

Check out this planting tray with mesh for seedlings on Amazon.

Of course, you may also plant your petunias in egg shells to make them easier to transfer later. Alternatively, you can use biodegradable planting trays that look like egg trays.

Click here to check this biodegradable plant starter tray on Amazon.

 Feed the seedlings with liquid fertilizer once in two weeks.

Once the seedlings have already established at least three strong leaves, you can then begin feeding them additional nutrients. Dilute liquid fertilizer in water and feed your petunia seedlings once every two weeks.

View this liquid plant food on Amazon.

Bring out the seedlings for full sunlight for 5 hours.

Real sunlight is important to your seedlings so they can grow stronger stems. You will know when it is time for them to get real sunlight once they have grown stronger leaves. However, do not let the seedlings sit under the sun for longer periods. If it is impossible to take the seedlings outside, you can place them beside a sunny window.

When is the Best Time to Transfer Petunia Seedlings?

A small garden filled with different kinds of flowers

Petunia seedlings should be ready to transfer once they have at least four real leaves. You can transfer them to pots or directly to the garden bed. 

Plant the petunia seedlings with 12 inches of space in between each if the area receives direct sunlight. You may need to plant them closer together if transferring to a shaded area. Petunias fully bloom when they receive a lot of sunlight. 

You should also check the soil temperature before transferring the seedlings. The ideal soil temperature should be around 60 degrees Fahrenheit. 

Final Thoughts

Replanting plants onto plastic pots on a table

While petunias bloom to their fullest under the sun, seedlings need more delicate care. But even so, petunia seedlings should not stop growing if they get proper warmth, moisture, and nutrients. Make sure to plant them in damp, fertilized soil with uniform temperature so they would continue to develop well.

For other helpful information about growing petunias, you may read our other posts:

10 Best Petunia Fertilizers That Will Produce Fantastic Flowers

Where To Buy Petunia Seeds (Top 30 Online Stores)