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Feed Me, Seymour

Fertilizing plants can be a bit bewildering but to get the most out of your plants, especially container plants, it is essential. This article will go over the basic types of fertilizers and give recommendations on when and how to apply those fertilizers.

Fertilizing plants can be a bit bewildering, but to get the most out of your plants, especially container plants, it is essential.  Have you ever wondered why some people and places seem to have larger, fuller plants?  The likely answer is regular fertilization and correct watering.  While many plants will do OK with little or no fertilizer, they will reach their full potential only with the correct nutrition.  However, fertilizer is one of those things where more isn’t necessarily better.  It is possible to harm your plants by feeding too heavily.

Fertilizing plants is an area that can be difficult to understand.  You stand in front of the fertilizer shelves at your garden center staring at the myriad options wondering, bloom booster, slow release, water soluble, N, P, K, micronutrients, bigger, more, better?  It’s enough to make a sane person, well, a little bit nuts. 

You can get really technical and bogged down in the little things when you get to talking fertilizer.  However, what most gardeners really want to know is what kind should I use and how often should I use it. 

The first question asked is often what are N, P and K?  ABC’s of Fertilizer gives a more in depth description of Nitrogen (N), Phosphorous (P) and Potassium (K).

The next question is what kind of fertilizer should I be using?  There are 3 main kinds of fertilizer: water soluble, slow release, and controlled release.  All 3 kinds have their positive and negative points.

Water soluble fertilizer is the oldest form of fertilizer.  The package you buy will be filled with either a crystalline or liquid fertilizer.  This substance is mixed with water, according to the directions on the package, and is normally applied every 7 to 14 days while you water.  Look for a formulation that has a fairly large N number (20 to 24 is good), a smaller P number - about half of N, (10 to 12 would be good), and a K number that is equal to or slightly less than N (15 to 20 is fine).  So look for a 20:10:20, 24:12:17, or 20:10:15.  This fertilizer ratio is a good bet for all types of fertilizer.  Follow the directions on the package for correct usage of your specific fertilizer.  Water soluble fertilizer is generally the least expensive form of fertilizer.


After water soluble fertilizer came slow release fertilizer which looks like pellets, about 1/3 of the size of a pea. Slow release fertilizers will slowly release a small amount of nutrients over a period of several months.  How much is released at a time is largely dependent on soil temperatures.  Microbes in the soil control how much slow release fertilizer is released at one time and the microbes are more active at warm temperatures than cool temperatures.  Slow release fertilizers can last for several months but since temperature has such a big impact it is difficult to predict exactly how long they will last.  Slow release fertilizers tend to be more expensive per package than water soluble, however, because you need to apply much less often they aren’t necessarily more expensive to use. 

The most recent addition to the fertilizer market are the controlled or time release fertilizers.  They are similar in appearance to slow release fertilizers but rather than working based on microbial activity in the soil they are largely controlled directly by temperature.  If temperatures are too cool no fertilizer is released.  However, when it is that cool plant growth rates are low so little fertilizer is necessary. Controlled release fertilizers are more exact and more expensive, than slow release fertilizers.  Controlled release fertilizers will last from 2 months to more than a year depending on the formulation you choose.  Choose your specific formulation based on how long your growing season is.  In other words annuals that will last for 4 months have no need for an 8 month fertilizer.  Shrubs and perennials would benefit from the longer term formulation.  The fertilizer package should tell you how long the fertilizer will last.

Slow and controlled release fertilizers are applied in a similar manner.  If you are planting in pots you can either mix the fertilizer into the potting mix as you add it to your container or you can top-dress.  Follow the package directions to determine how much to add to each pot.  Top-dressing  (photo, left) is when you add the desired amount of fertilizer to the top of an already planted pot.  It is best if you can mix the fertilizer into the top couple of inches of soil but it will be OK if you can’t.   

If you are planting into the landscape add the appropriate amount of fertilizer into the hole before placing the plant (consult the package for specific amounts).  Be sure to mix the fertilizer into the soil at the bottom of the hole.  Roots can be burned by direct contact with slow release fertilizer.  If you are applying to an already established planting, top dress according to the directions on the package.

So should you use a water soluble or controlled/slow release fertilizer?  In general I think most people are best served using a controlled or slow release fertilizer.  You apply it once or in some cases twice a growing season and then just water as necessary.  You don’t have to mix up fertilizer every week or two and your plants should be perfectly happy.

There are times when it makes sense to supplement your controlled release fertilizer with an application or two of water soluble fertilizer.

  • If you have plants in pots that are “heavy” feeders (those that need a lot of nutrition), such as Supertunias®, you may want to use a water soluble fertilizer every couple of weeks to boost the nutrition level.  Heavy feeders planted in the soil are taking advantage of the native fertility of your soil and shouldn’t need the extra fertilizer.
  • If you have gone through a long rainy period or had a very heavy rainfall, an application of water soluble fertilizer will return some nutrition to your potting mix (what was there has likely washed away in the rain) and help your plants rebound.
  • If your plants have grown very large supplemental water soluble fertilizer may help them maintain lush growth.

Plants will only need fertilizer during active growth periods.  So if the plants are dormant don’t bother feeding.  If the plants are actively growing you should be fertilizing.  Be careful not to over fertilize in early spring (only a problem with water soluble fertilizers) when cooler temperatures mean plants aren’t growing as much.

558 Readers Rated This: 12345 (3.2)
Anonymous's picture
Anonymous Sat, 07/08/2017 - 10:46am

I would like to know if this product can be shipped to Canada, or if it is available at retailers in British Columbia.

Sarah Geoghegan's picture
Sarah Geoghegan Mon, 07/17/2017 - 11:31am

Yes! We do ship plant food to Canada.
You can order here:
Proven Winners

Anonymous's picture
Anonymous Sun, 07/02/2017 - 6:27pm

I just picked up this plant food at the store and was wondering if it's ok to apply to foliage and blooms of plants. My watering can has a permanent shower spray nozzle and it is hard to water just the soil at the base of the plant. Will it harm the plant/blooms to water this way or should I get a new watering can with just a spout?

Sarah Geoghegan's picture
Sarah Geoghegan Mon, 07/17/2017 - 11:16am

Direct watering with the Water Soluble Plant Food will not harm the blooms/foliage at all!
Happy Gardening!
Proven Winners

Anonymous's picture
Anonymous Fri, 05/20/2016 - 8:10pm

Can I use this plant food on all of of my plants or is it just for the petunias/pansies and others that I used to use miracid on?
Is it OK for Zinnias, sun-patens, etc.?

Kerry Meyer's picture
Kerry Meyer Tue, 05/24/2016 - 10:26am

It is fine to use on all flowering ornamental plants.

Anonymous's picture
Anonymous Sat, 05/30/2015 - 8:53am

5/30/15: I recently read in our local newspaper that heavy feeders like petunias and geranimums need to be fed every few days. So I fed my Bubble Gum PW petunias liquid Miracle Grow on a Sunday and then the following Wednesday, and now just a couple days later am wondering whether I over-fertilized them, as they've started to lose their color. Any thoughts about this problem?

Anonymous's picture
Anonymous Sun, 05/01/2016 - 8:50pm

Either fertilize much less twice a week or only fertilize once a week based on your technique I would fertilize once a week even then you will know if it is too often when you see bleaching of the flower color

Kelly Geoghegan's picture
Kelly Geoghegan Mon, 06/01/2015 - 4:35pm

We recommend using our fertilizer every third watering. With Supertunias make sure the soil is completely dry before the next watering.

Hope this helps.

Kelly Geoghegan

Anonymous's picture
Anonymous Wed, 07/09/2014 - 7:38pm

Help!, my instructions on the bottle are not intact the bottle must have got wet at the store. when I peeled the label it all stuck together and I don't have any information on how much food to give plants in baskets and ground

Marissa DeVlieger's picture
Marissa DeVlieger Mon, 08/18/2014 - 6:41pm

Here are the instructions as they appear on our Premium Continuous Release plant food:

"Potted & Container Plants: When planting into the following container sizes, use the following raters and water in thoroughly. Reapply after six months.

Container Size
(Diameter in inches) 4-------6-------8(1 gallon)
Amount (teaspoons) 1------1.5------3

Container Size
(Diameter in inches) 10-------18-------24
Amount (tablespoons) 2--------4--------8

Planting into the landscape:
New Transplants: Use the rates from the chart above that correspond with the container size you are planting. With container or cell pack sizes smaller than 4 inch, use a rate of .5 teaspoon per plant. After planting, sprinkle the plant food evenly around the plant. Or, before planting, mix the plant food with soil in the planting hole and place plant in the hole. Water in thoroughly. Reapply after six months.

Established plants: Apply 8 tablespoons of plant food for every 5 ft. x 5 ft. area of garden. Apply evenly on the soil surface. Or, work plant food into the top 2 to 3 inches of soil. Water in thoroughly. Reapply after six months."

Anonymous's picture
Anonymous Sat, 05/24/2014 - 7:28am

A friend told me not to use miracle grow on my potted tomato plant. She said use a 10, 10, 10. Is this good advice and can you tell me why?

Anonymous's picture
Anonymous Sun, 04/30/2017 - 8:36am

I really really dislike miracle grow. I will never ever use it in my garden. I am not sure if it is because they say they are time release, but aren't really or what is going on with them but they will either over fertilize or under fertilize your plants and it seems like their estimated amounts in their fertilizer (the 10, 10, 10) is way off to me. You will see your plants burned after using miracle grow or never really prosper. Anyways miracle grow (for some reason) seems to be what every new gardener goes for. Every time I see someone I tell them what I said here. And also 10 10 10 is not a good number. Remember Plants that are known for their prolific flowering abilities will generally need more phosphorous. This is the middle number is most fertilizers. A 10-20-10 will contain a higher dose of phosphorous to help nourish your flowering plants. [7]

Anonymous's picture
Anonymous Thu, 06/05/2014 - 5:01pm


Anonymous's picture
Anonymous Tue, 12/10/2013 - 10:45pm

organic ones supplied by natural systems. We can replicate or these systems and produce wonderfully healthy gardens. Cheers!

Anonymous's picture
Anonymous Sat, 07/20/2013 - 4:48pm

I use the indoor plant instructions for the liquid fertilizer when I water my hanging baskets. I use it every time I water. On the very continuous hot days when I water twice (if my gardening water meter reads that I should do so) I only use it once. Am I doing the right thing or should I back off adding the fertilizer every time I water.

Kerry Meyer's picture
Kerry Meyer Tue, 05/20/2014 - 1:54pm

Using a weak fertilizer solution every time you water is a perfectly valid way to fertilize your plants.  If your plants are performing well, there is absolutely no reason to change what you are doing.  Success is success!


Kerry Meyer
Proven Winners

Anonymous's picture
Anonymous Fri, 07/19/2013 - 6:26pm

What is the shelf life of water soluble granules? I have some that is at least 5 years old.

Kelly Geoghegan's picture
Kelly Geoghegan Wed, 04/23/2014 - 5:10pm

Our Proven Winners Water Soluble Fertilizer will not go bad!

Hope this helps! Kelly Geoghegan PW

Anonymous's picture
Anonymous Fri, 07/19/2013 - 3:38pm

This is a very well written, informative article. it's a keeper! The timing is flowers look just like Kerry's description.
I'd like an article to address the plants that love acidic hydrangeas and rhododendron.

Thanks and God Bless YOU!

Anonymous's picture
Anonymous Fri, 07/27/2012 - 8:01pm

what kind of fertilizer, does Hydrangea like best? My Blue Nikki does not have any buds, but looks very healthy. Any suggestions why?

Anonymous's picture
Anonymous Fri, 05/23/2014 - 9:04am

If you are in a zone that is too far north, you might have lost the flower buds through dieback over winter. Macrophylla hydrangeas have that problem, and if it gets too cold you get nice healthy leaves but no flower buds. The new hydrangeas that bloom on old and new wood helps, but Nikko Blue is not one of them.

Anonymous's picture
Anonymous Fri, 07/19/2013 - 4:01pm

Hydrangea usually like a acid fertilizer like Hollytone or Miracid. However, I don't thing lack of fertilizer has stopped your Hydrangea from blooming. Even though they like shade, they do need a bit of sun to bloom. I had to move some of mine to part sun to bloom. Or-the plant is too young or pruned at the wrong time of year. I too have a Nikko Blue and it took 3 years before it bloomed.

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