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Petunia Seedlings Not Growing – What To Do?

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 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. Make sure the temperature is right
  4. Do not plant the seeds too deep

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

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

Why Aren't My Petunia Seedlings Growing?

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 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 a seed starting mix or make one.

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 can hold water well. Peat moss gives lasting moisture as it decomposes slowly, whereas vermiculite holds air that helps fluff the soil mix.

Small growing petunia plants growing at the garden

Compact and dry soil does not make a suitable 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 white spots on leaves and yellowing leaves. The seedlings will damage their roots when left in the same situation for extended periods.

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. Keep the 6-8 inches of topsoil moist as a guide until the seedlings have grown their roots.

Make Sure The Temperature Is Right

Petunias love sunlight, but the case is different for seedlings. Direct exposure to sunlight for extended periods is a lot for the seedlings to handle and is probably 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. Also, check the temperature between 60 and 65 degrees Fahrenheit and keep it on for 12 to 16 hours.

Keep your seedlings under the same condition until they have established at least three leaves. You can place your petunia seedlings near the window if a fluorescent light source is unavailable.

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. 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 tiny size makes it challenging to plant petunias, so 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 crucial when starting 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, ensure they germinate right in time, and grow to full bloom without problems?

Plant During The Frost-Free Seasons

You should plant your petunia seeds ten 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 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 receive 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 essential 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 established at least three strong leaves, you can 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

Natural sunlight is vital to your seedlings so they can grow stronger stems. You will know when it is time for them to get natural sunlight once they have grown stronger leaves.

However, do not let the seedlings sit under the sun for extended 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 move 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 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.

Our Final Thoughts

Replanting plants onto plastic pots on a table

While petunias bloom to their fullest under the sun, seedlings need more tender 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 temperatures so they would continue to develop well.

Made it to the end? Check out these helpful related articles below:

10 Best Petunia Fertilizers That Will Produce Fantastic Flowers

Where To Buy Petunia Seeds (Top 30 Online Stores)