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Why Your Petunias Aren’t Blooming and 7 Practical Fixes

Why Your Petunias Aren’t Blooming and 7 Practical Fixes

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Petunias are grown for their bright colorful petals and lush fragrant scent. They’re the epitome of summer bedding plants and floral window boxes. Being summer plants, when you have petunias not blooming, you’re missing out on everything the plant symbolizes.

Solving the Mystery of Why Petunias Won’t Bloom (or Stops Flowering)

1 – Not Enough Light to Meet Their Needs

For petunias to bloom, light is the backbone of everything. It’s needed for photosynthesis. No amount of fertilizing will compensate for a lack of sunlight. It’s the most important facet of petunia care.

The more light these receive, the more greenery they produce. That, in turn, helps the plant absorb more energy from the sun’s rays, convert that to sugar, and throw loads of energy into producing buds.

The more buds you have, the more flowers you get. Pick them off and it encourages side shooting or branching, and then you can get even more gorgeous florals.

None of that is possible if the plants are located in a shady location – even if it’s only for part of the day.

Petunias are full-sun plants, necessitating at least 6 hours of full sun daily to have a chance of blooming. They can cope with five hours, but the more light they receive, the more flowers they produce.

These top the list of container plants for full sun, able to cope with direct sunlight all day (even in the afternoon heat) and without the leaves scorching. 8 hours of full sun is what to aim for to get the most prolific blooms from petunias. Starve them of bright light, they can stop blooming.

For those unsure of what light requirements for plants mean, the best way to describe ‘full sun’ is the amount of light the plant receives from all directions throughout the day. It’s the equivalent of plants in nature in a summer meadow.

No sheds, trees, walls, or outbuildings obstruct sunlight at various times of the day, such as when an overshadow is created as the sun moves. Observe yours at different times of the day to see if they’re being left in partial shade for an hour or two.

Petunias, being heavy feeders, need all the light they can get to capture the energy needed for consistent blooms right through the summer.

2 – Infertile Soil

When planting petunias in garden beds, or in containers that’ll be placed outdoors, it helps to give the plants a running start. Do that by planting them in soil that’s been prepared with a good mix of a balanced granular fertilizer that’s been worked in at a rate of around 2 lbs per 100 ft2.

The reason to start them in a mix enriched with balanced nutrients is to help with all-around growth, which is the root and leaf development phase. With nutrients already in the soil, extra feeds will be supplemental rather than the only nutrients the plants receive.

3 – Fertilizing with the Right Nutrients and at an Appropriate Frequency

The soil is only the start. Throughout the season, liquid fertilizer needs to be applied as a nutritional supplement. Petunias are heavy feeders so they don’t perform well when left to fend for themselves.

At a minimum, they’ll need a liquid fertilizer added every few weeks throughout the growing season. What type of fertilizer to use is what you need to determine.

There are a few ways to approach fertilizing petunias. The first, (and most common), is to use a balanced fertilizer. That’s when all three digits on the label are equal, representing an equal amount of nitrogen, phosphorous, and potassium.

The second approach is to use a fertilizer that is higher in phosphorous. Another method (and possibly a more advantageous one), is a hybrid of the two. It depends on the amount of rainfall your petunias are exposed to.

Here’s the reasoning behind the recommendation of different fertilizers…

  • Nitrogen is responsible for the green in plant leaves. Trouble is that it can be rapidly flushed from the soil by a period of intense rainfall.
  • Phosphorous is responsible for flowering. That’s why fertilizers with a higher amount of phosphorous in comparison to the other two nutrients are referred to as bloom boosters. They promote flowering, but at the expense of everything else, it means the blooms will be more proficient, but short-lived.
  • Potassium is what’s needed for healthy root growth.

To keep petunias in bloom, they need a healthy dose of all three primary nutrients.

If you were to be growing petunias in a window box, sheltered from rainfall, the balanced fertilizer all the time may be sufficient. When dealing with runoff and nutrient leaching in flower beds though, that’s when you may want to venture into different fertilizers at different times of the season.

When you first plant your petunias in the garden, or their hanging basket, feed them with a balanced liquid fertilizer at the start of the season. Then, as the plant matures, has strong enough roots established, and plenty of greenery, switch to a fertilizer that’s slightly higher in phosphorous to encourage blooming.

That way, the early balanced fertilizer gives the plant the nutrients required for all-around growth, and then when it’s ready for flowering, it gets an extra boost.

If you want to keep your petunias blooming, rotate between balanced feeds and a high phosphorous fertilizer so that the leaves and roots are continually being nourished rather than being sacrificed for promoting flowering. If the roots and leaves are neglected for long enough, blooming is likely to be impeded.

4 – Nailing the Watering Routine

Watering petunias too much, too little, or if the soil isn’t draining fast enough (causing water to stagnate), petunias won’t perform well at best, and at worst, it could be fatal for them. It is easy to go overboard with watering or to dehydrate the plant. The color of the leaves indicates if petunias are experiencing stress from inadequate watering.

Leaves on petunias turning yellow are indicative of dehydration. Overwatered petunias develop brown leaves and display wilting. Petunia leaves turning brown is a real cause for concern because it’s indicative of root damage.

Too much water is worse because it can lead to pooling on the topsoil, which then reduces oxygen reaching the roots. That’s when there’s an elevated risk of root rot developing owing to reduced oxygenation levels in the soil mix.

5 – Overcrowding Petunias in Containers or Flower Beds

Overcrowding containers or flower beds is going to lead to the roots competing for nutrients. Without enough to go around all the plants, each will receive fewer nutrients, leading to deficiencies, which eventually will decrease flowering. Potentially to the point that petunias stop blooming completely.

To ensure all plants get equal and sufficient feeding, space each plant at least 1 inch apart.

6 – Planting in Too Small of a Container

Similar to overcrowding in pots, too small a container can have the same symptoms as overcrowding, but caused by a different type of problem. Smaller containers can’t hold as much soil so it stands to reason, there are less nutrients available to feed all of the roots.

The smaller the container is, the less soil it can hold, and the less soil there is, the less nutrients are available. Add to that the exposure to rainfall causing nutrient leeching, the effect is a nutrient deficiency, despite your best efforts to keep the plant well nourished.

An indication of this happening is when your petunias start the season well, then after a month to two months, blooming declines to the point the plant has essentially stopped blooming. The slow (but noticeable) decline in flowers can indicate that rainfall or watering frequency is flushing nutrients from the soil far too fast.

To speed up the recovery process and get the plant blooming sooner, repot it in a fresh potting mix that has a granular fertilizer mixed through it. Leave it for three weeks with only water being added, then introduce a fertilizer with a higher level of phosphorous to promote flowering.

Go back to a balanced fertilizer though otherwise, the root and leaf development may be reduced. That would lead to reduced flowering later in the season.

7 – Overgrowth

Deadheading goes part and parcel with petunias. The blossoms are short-lived, but given the consistent production of buds during the warmer weather, you’re unlikely to notice it.

When flowers are pinched off, new ones grow in very soon after. With practice, you’ll likely find yourself sacrificing flowers here and there to make your petunias fuller.

Ultimately, the fix for petunias not blooming boils to the plants receiving less than 6 hours of FULL sun, dehydration, or too much water affecting soil drainage. That introduces the problem of nutrient leaching.

When nutrients are flushed, the plant will develop a nutrient deficiency, which is when you’ll notice the decline in flower production, regardless of how much fertilizer you add.

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