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Petunia Care: How Much Sun, Water & Fertilizer Do Supertunias® Need?

petunia care
Supertunia® Bordeaux Petunia


Here are some basics to help you succeed with petunias in your garden! The three big requirements are:

  • Sun
  • Water
  • Fertilizer

These are the three things you must keep in mind to have the best performance from your Supertunias.


Petunias need AT LEAST 6 hours of full sun a day for best results. So from 10:00am – 4:00 pm minimum.

Think of it this way, for Supertunias sun = energy – they need this energy to keep producing more flowers, because flowers require energy to produce. The more energy the plant has the better the flowering. With sun and Supertunia more is almost always better!

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Petunia plants like consistent water. They can tolerate a little more or a little less, but the key is to be consistent. The more they receive their needed water on a regular basis the more reliable they are in producing new flowers. 

Things get dicey when someone forgets to water and plants become very dry, or if someone gets carried away and makes the plant soggy. Those extremes are harder for the plant to deal with than regular watering. When the plant is stressed by the extremes, they stop producing flowers and just try to survive – you never want your flowers to have to make that decision!

The amount of water a plant needs is always changing, here are tips for watering your petunias:

  • Have a regular day every week that you water, and as the season progresses and you need to water more often, have a few regular days every week, always trying to be consistent. 
  • Petunias planted in pots, window boxes or hanging baskets will need more frequent watering than those planted in landscape beds.
  • In spring when there is rain and cool nights they just need enough water to keep them moist. 
  • As the summer progresses (especially in pots) the heat, sun, wind, and pot size all cause the plant to need more water. 
  • Then as fall settles in and night temperatures get cool again you’ll see plants stay moist longer with each watering and need less water overall.


If sun = energy, and water must be consistent, then fertilizer = food. It is hard to get up each day and produce 50 new flowers without having breakfast. Think of how hard it would be to go to work without any food for a day or so. Fertilizer is essential for Supertunias to do well; they need nutrients like we need food – everyday. So does that mean you need to fertilize daily? No. Because to a certain extent where your plants are located or planted has a big effect:

Planted in the ground:

They have it easy, they have unlimited space to grow and if they can’t find the food they need they can send their little roots out farther to find it. Think of the average garden plot in your yard as a bank, there is almost always some water and some nutrients available for loan, so it provides a bit of a fudge factor when watering and fertilizing. As a result, plants planted in the ground can do with a bit less fertilizer and water than plants in containers.

Planted in containers:

This is a bit more complicated because in a pot the soil "bank" is gone. There is only so much room in a pot for soil and only so much water that can be held by the pot and saucer, and there is no place to go when fertilizer or water runs out. Also potting soil is usually an artificial soil that does not have all the nutrients and good qualities of garden soil. Potting soils make it necessary to provide ALL nutrients to plants, as most do not have nutrients already in them. So plants in containers need to be babied along by providing for their needs and that means regular watering and complete fertilizing.

caring for petunia
Supertunia Mini Vista® Indigo

What kind of fertilizer should I use? 

Actually any number of fertilizers will work just fine, but there are some differences.

Organic Fertilizers: 

Many folks love organic fertilizers and they work well. Examples include:

  • fish emulsion
  • blood meal
  • bone meal
  • compost tea
  • etc

They do not provide supercharged levels of nutrients, but they do supply a lower level of a balanced diet. Most organic fertilizer needs to be reapplied every 3-4 weeks to keep fertilizer levels where plants need them all season. 

Usually an organic fertilizer needs to be mixed into the soil around the plant and not just scattered on the soil surface.  Why? Because all organic fertilizers require soil bacteria to break them down into small enough bites that your plants can take them up – most of the time there are always plenty of helpful soil bacteria to do this. Because bacteria are needed; in the spring organic fertilizer may take a few weeks to breakdown, so make sure your plants get enough food early in the year!

Non-organic fertilizers: 

This sounds bad, but it is not in most cases. Non-organic fertilizer is plant food in its ready to eat form, so you don’t need as many bacteria and the results are more immediate. 

Make sure your fertilizer is a ‘balanced’ fertilizer, just like humans need a balanced diet. How can you tell? Read the label and see what is in the fertilizer before you buy. It is a bit like taking vitamins, a good multi vitamin provides all needed vitamins & minerals, the same is true for a good fertilizer. 

A balanced fertilizer should supply all of the following: Nitrogen, Phosphorus, and Potassium. These are the three numbers on the front of many fertilizer bags, they usually show up like this 18-6-12, or 14-14-14. It is just a simple way to show what the percentage of each are in the fertilizer. 

BUT…that’s only part of the story, you also need all the other nutrients (calcium, magnesium, sulfur, boron, chlorine, copper, iron, manganese, molybdenum, zinc and nickel) and that is where reading the back of the label comes in handy. Check for these nutrients as well and you if they are there – you have a balanced fertilizer! Remember, for plants living in containers, they have no way to get these essential parts of their diet unless you supply them!

Proven Winners has some great plant food that you can find on this page:

How often do you need to fertilize with non-organic fertilizers? 

It depends on how you apply them, here’s a quick reference:

  1. Liquid (or mixed with water) – these fertilizers need to be applied about every 1-3 weeks (depending on the amount of rain you are getting, or how often you water because these fertilizers will wash away in water and then you need to apply more), although if you use drip irrigation you can apply with every watering – this is a great way to take care of plants, it is the MOST efficient way to take care of them if you can!
  2. Granular fertilizer – are dried chunks of fertilizer that last a bit longer than liquid types so you apply them by scattering over the soil around the plants. This type of fertilizer breaks down over a period of week so needs to be reapplied every 3-4 weeks (but don’t forget a lot of rain or watering will wash it down past the roots as well) so heavy rains usually require you to fertilize again.
  3. Slow Release fertilizers – these are very helpful fertilizers but a bit more expensive, here’s why. The fertilizer is wrapped in a hard shell so it lasts and lasts. Depending on the type of shell it can be applied once a month of even every 6-8 weeks. A big time saver and it reduces run off of excess fertilizer into the soil. Proven Winners carries a slow release fertilizer that is very good!  


Most petunias benefit from deadheading -- the process of removing spent flowers to encourage more blooms. However, Supertunia® petunias are self-cleaning, with no deadheading necessary. If you are a time-starved gardener, these are the perfect petunia to grow. However, if your plant begins to look open or a bit tired, an allover trim can be beneficial. Learn more about deadheading.


April – Or whenever spring comes in your location.

  • When you buy in the spring, buy a slow release fertilizer to top dress the basket or container. If you plant your own basket, incorporate some of the slow release fertilizer in the soil as you plant. Follow the package directions.

May - fertilize with a water-soluble fertilizer once every two weeks.

  • Mix up the fertilizer and water the plants just like you would if you were using clear water. It normally takes a good half of gallon of water to really water a 10" wide basket or raised container.

June - as the weather starts to get warm to hot, fertilize weekly, again with a good soaking.

  • If the weather turns really hot as it sometimes does in Late June you may need to fertilize every third watering. By now the Supertunia is really growing and starting to tumble down from the basket or fill out across the flowerbed.

July - is when the cutting back occurs.

  • Around the 4th of July, (after your big party) get some of the slow release fertilizer that you bought in spring and re-apply across the top of the planter. By now with July's heat you should be watering at least every other day and begin to fertilize every other watering. I know it sounds like a lot, but if you want a plant to grow like an elephant and be the most it can be, you got to feed it like an elephant!

  • At the same time, trim back some of the longer branches just enough to bring the plant back in line with the bottom of the pot or basket. Don't remove too much at the maximum cut back 20% of the branches or 1 in five shoots. You can also just give it a general light trim. Your plant will be out of flower for a few days, but will come back stronger than ever.

August - is, hot, humid, & sometimes with monsoons. Keep up the water and fertilizing.

  • Again, if the plant starts to look straggly remove a few more branches but never more than 20% or give it a general trim as before.

September - The plants should still look good, as you start to back off the watering and the feed

  • Shape the basket with the last pruning of the season. Hopefully this will now carry you through until frost!

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NOTE: For folks in the deep south – your calendar will likely start & finish earlier. For the deep south most Petunias struggle in August heat and humidity, as well as the afternoon rains, so expect petunia season to end usually in late-July or mid-August. To extend your season, move planters under protection from rains, but make sure to keep them in the sun for best flowering.

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