Why Are My Petunias Not Growing and Flowering? Here’s Why

In rare cases, where the growing conditions are not favorable, petunias may not grow well and may refuse to flower. Fortunately, the problem can usually be diagnosed and fixed. Most often, the culprits may be insufficient light, nutrition and overwatering. Read on to learn more. When it comes to easy care for ornamental flowering plants, petunias are hard to beat – they can easily deal with unfavorable conditions, reach flowering maturity in less than 2 months from seed, and produce colorful flowers all throughout the warm months. Petunias have only 2 disadvantages

1. They are easily killed by frost.
2.  Letting them self-sow will usually produce differently colored offspring, due to the fact that most seeds sold on the market are hybrids.

What Problems Are Common When Growing Petunias?

Although Petunias are usually very resilient, they can experience many of the problems common with other garden plants. Those include fungal diseases, growth problems caused by insufficient nutrition and wilting due to overwatering. Wilting is particularly common in petunias, just like it is in their close cousin, the tomato. Some wilting after transplanting is normal and generous misting should fix the problem. The plants usually recover in a matter of days. Providing some shading can also help. However, if the problem develops unexpectedly and gradually worsens, this may point to root rot, which is usually caused by overwatering. Various fungal diseases and insect pests may also be the culprit. Examining the plant for aphids, scale insects or other bugs and checking the lower stem for fungal rot can quickly diagnose the issue.

What May Prevent Petunias From Flowering Or Cause Them to Stop Flowering?

In almost all cases, the problem is lack of light or lack of nutrition in the soil. In both of those cases, the plants will also grow unexpectedly slowly and will fail to develop the foliage necessary for flowering. Slow growth can also be caused by soil that is too compacted and kept overly wet. It’s uncommon for petunias to grow good foliage, but still refuse to flower – if that’s the case, make sure that you’re not being overly impatient and give them some time.

Here are a few things to try if your petunias are not flowering:

Wait

Petunias thrive on neglect – the impatient, overly-caring gardener may be one of their biggest enemies! Many gardeners expect petunias to start flowering as soon as spring arrives, constantly checking on them and fertilizing or pruning them. This often does more harm than good. Generally, it takes about 1.5 – 2 months for petunias grown from seed to start flowering. Newly transplanted plants may need a full month for acclimatization and root development before they decide to start forming flower buds. And in colder climates, petunias may decide to flower a bit later, with the arrival of summer. Flowering can also be delayed due to low-light conditions.

Apply fertilizer

Fertilization can be a double-edged sword, and it can be difficult to determine if the lack of flowering is caused by nutrient deficiencies. Applying a balanced fertilizer with enough phosphorus (the middle number in the three-number NPK label being higher than (10) can stimulate flowering, but over-fertilization can easily damage the plant. Usually, fresh, new soil supplies plenty of nutrition on its own. If the plant starts forming less and less new flowers and its growth rate slowly declines, this is usually a good sign that fertilization may be required. For more information about fertilizers, click here. 

Remove old flowers (deadheading)

If your petunias are blooming well during spring, but flowering stops or slows down unexpectedly, the first thing to try is removing all the dying flowers. The plant may have redirected all of its energy toward seed development and not toward new flower formation and getting rid of the forming seed pods quickly solves this issue. If you want to learn more about deadheading, click on the link below.

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Make sure the plant gets enough light

Without at least 6 hours of good, direct sunlight, the plant won’t have enough energy for proper flowering. Petunias growing in pots can be easily moved to a more suitable location. For plants growing in garden beds, the only option may be to remove nearby obstacles that block the sun. Nothing can compensate for lack of sufficient light.

Inspect the plant for diseases

Petunias aren’t prone to diseases, but it’s worth inspecting the plant and making sure that it isn’t suffering from fungal pathogens or insects. Rotting stems are a sure sign of a fungal infection and a good fungicide spray can solve the problem. Fungal problems usually develop because of too frequent watering. The TMV (tobacco mosaic virus) virus can infect petunias and there’s no cure for it – the only solution is to remove infected plants to stop the spread.

What Causes Petunias to Lose Leaf Color or Look Sick?

Over-watering and soil compaction may be the cause. The lack of oxygen that comes from over-watering may cause anaerobic bacteria to thrive, producing too much ammonium, which can be toxic to the plant. This is a difficult problem to diagnose and solve, which is why a good all-around solution for sick petunias is to repot them in new soil. When it comes to nutrition, the symptoms of nutrient deficiency can often be the same as those of over-fertilization, making this a tricky problem to diagnose. If the plant starts looking sick after regular fertilization, consider over-fertilization and nitrogen toxicity as the cause. If the petunias are planted in old, spent soil, consider nutrient deficiency as the cause. And lastly, consider fungal diseases, the tobacco mosaic virus or insect pests as the cause, as we already explained in the previous section.

Optimal Growing Conditions During Warm Months

How much sunlight do they need?

Petunias require at least 4 to 6 hours of direct sunlight every day. Without direct sunlight, they grow too slowly and in extreme cases may never reach the mature stage when they are ready to bloom. Usually, lack of light doesn’t completely stop flowering, but it greatly reduces the number of flowers and delays the onset of blooming. Petunias growing in poorly-lit areas may flower in mid-summer, as opposed to in mid-spring. What Temperature Do They Grow Best At? Frost will damage petunias, but temperatures of around 40F (4C) aren’t harmful to them. They have little trouble dealing with the summer heat, but newly transplanted plants may wilt and die if not properly acclimatized to it. Petunias are actually a short-lived perennial plant and in very warm climates, above USDA zone 10, they may survive winter and start blooming again as spring arrives.

Best Soil For Petunias

Petunias thrive in regular, general purpose potting soil. The only requirement is that the soil shouldn’t be too compacted. Old, spent soil can result in very poor growth and yellowing of the leaves. Mixing in some fresh compost in the old soil can solve that problem and so can modest fertilization with a balanced fertilizer. High-phosphorus fertilizers, which are all fertilizers marketed as being suitable for flowering plants, can encourage blooming. High nitrogen fertilizers that lack phosphorus may stunt flowering.

Watering Needs

Petunias should be watered thoroughly, so that the water penetrates deep into the soil. Watering with small amounts of water may prevent the root system from growing deep enough, which can cause poor growth and poor flowering. That said, the watering frequency shouldn’t be too high or root rot may develop. A watering frequency of around once a week is usually ideal for outdoor Petunias.

Is Planting In Pots or In Raised Garden Beds Better?

Petunias can be successfully grown in pots, which gives you more control of the placement and arrangement. Pots larger than half a gallon are recommended – small pots will dry out quickly and the plants can easily die if you forget to water them. When planting petunias in pots, provide around 6 inches of spacing between individual plants.

Can Petunias Be Grown Indoors?

Petunias are not very practical for growing indoors. When sunlight comes from a window, the bushy structure of the plants prevents even illumination of the foliage, leading to poor growth and flowering. However, there are exceptions. Petunias grow very well on south-facing balconies.

Pruning to Stimulate Node Development

Without pruning, petunias grow one main stem without much side branching. This can limit the number of flowers that form. To avoid that, it’s recommended that you pinch off the top of the plant every so often – every 2 weeks or so. Pruning is also said to stimulate flowering and is one of the first things you may want to try if your petunias refuse to start blooming. Check out these Amazon picks below.

My Petunias Appear to Be Dying! What Should I Do?

If your petunias are getting enough light, but they still appear to be dying, the first thing to do is to inspect them for fungal diseases and apply fungicide if necessary. Here’s a good article on the different types of fungal treatments available. Distorted foliage, yellowing or brown spots can all point to a fungal pathogen. Fungal pathogens often develop because of an overly thick canopy, combined with excessive watering from above. This lets water accumulate on the stems for too long, creating a suitable environment for pathogenic fungi. In cases where the cause of the problem can’t be determined, a good solution is to simply repot the plants in fresh soil. Compacted soil that has been kept overly wet for a long time can accumulate too much ammonia and throw of the pH levels, creating a phenomenon known as ‘nutrient lockout’. This is not a common problem with petunias, but it can still happen. Mixing the soil around and aerating it, while adding aeration-promoting amendments like perlite, can solve the problem without the need of purchasing new soil. Mixing in fresh compost can also help renovate the soil.

Compensating For Unfavorable Growing Conditions

Petunias can deal well with unfavorable growing conditions, but there’s nothing that can be done to compensate for lack of light – without sufficient energy that comes from photosynthesis, the plants will simply not have the energy to grow well and produce flowers.

Do Unfavorable Conditions Affect All Varieties The Same?

There are around 20 species of petunias and just 4 ‘main’ varieties, which can be easily distinguished by the color and the size of their flowers. Those are grandiflora, multiflora, milliflora and wave petunias. However, they all have identical care requirements, so proper identification is not required. Letting petunias form seeds and planting those seeds will not usually produce identical offspring, because most seeds on the market come from hybrid pollination.

Final Thoughts

Petunias are easy to care for and you are unlikely to encounter any serious problems while growing them. If your petunias are not flowering, the best thing to do is make sure the basic growth requirements are met and wait. Diseases are uncommon and easy to spot and can be deal with by the use of fungicides or insecticides.