Do My Perennials Need Fertilizer?

When it comes to caring for your perennials, you might be wondering if you’ve been skipping a very important step. You’ve heard about fertilizer and know it’s supposed to help boost plants’ growth, but do your plants need it? When it comes to fertilizer, also known as “feeding” your plants, there is actually quite a bit to know before we answer the question about whether or not your perennials need it.

perennials fertilizer

Let’s first look at the basics of fertilizer for perennials.

Fertilizer Basics

Fertilizer contains many nutrients plants need but  sometimes cannot get from the soil and the air. That’s where the fertilizer comes in—to replenish some of those nutrients. In all mixed fertilizers, there are three main chemical ingredients worth noting.

  • Nitrogen: Promotes healthy leaf growth because nitrogen stimulates the production of chlorophyll. In case you need a refresher, chlorophyll is the main chemical involved in photosynthesis, which is how plants convert sunlight to food—so extra chlorophyll production is a good thing.
  • Phosphorus: The chemical phosphorous supports the vigorous development of some of the most important parts of the plant: roots, stems, blossoms, and fruits.
  • Potassium: Not only great for humans, potassium in plants helps them digest and manufacture their foods.

Different types of fertilizers have these ingredients in varying ratios. Before you go adding fertilizer to your plants, there is still more to know. For example, more fertilizer is not better—if you over-fertilize or fertilize at the wrong time, you can risk burning the roots of your plants and killing them. When deciding if your perennial needs fertilizer, first consider the soil it is already growing in and what types of nutrients are already present. It’s suggested to get your soil tested so you can correctly diagnose which type of fertilizer is needed to assist in bigger blooms.


Natural Fertilizer Vs. Synthetic Fertilizer

To make your decision more difficult, there are a lot of fertilizer types and options out there. We hope to clear up some confusion for you.

Natural fertilizer

Organic gardeners may want to go the natural route with their fertilizer. Natural fertilizers contain organic ingredients from plants and animals—manure, bone meal, and fish meal are common. Organic fertilizers have a wider variety of nutrients in smaller concentrations than synthetic fertilizers.

Synthetic fertilizer

These manufactured fertilizers use chemicals, including ammonia, natural gas, nitrogen from the atmosphere, phosphate minerals, and potash to be produced. They are common in most garden centers and contain a big blast of the core three nutrients mentioned above in precise ratios and concentrations. One of the most common synthetic fertilizers is the all-purpose 10-10-10 N-P-K (nitrogen, phosphorus, and potassium) variety, which contains 10% of each active ingredient.

Why not use synthetic fertilizers?

Well, some plants don’t need such a large amount of nutrients. Even though the plants eat the nutrients very quickly, you can still overdo it with this type of fertilizer, hurting your plants. With an organic fertilizer, because the nutrients are more varied, the plants eat them slower, causing a more controlled growth process. Additionally, synthetic fertilizers are usually highly water soluble and can drain into streams and lakes, kickstarting growth of invasive species and algae.

Speaking of water soluble fertilizers, it is worth looking into whether you should be using a granular fertilizer, which takes longer to absorb and offers longevity, or a water soluble fertilizer which is consumed quickly but requires more frequent application. This article gives a good rundown of your options.


Which perennials need fertilizer?

The question now arises: Should I be looking into fertilization options for my perennials? Well, if you’re a little intimidated by the world of fertilizers, there’s good news. Most perennials actually don’t need much fertilizer to thrive, and some don’t need it at all!

If your soil was rich and well-prepared at planting time, most of your perennials will probably do fine with a layer of compost at springtime. If your plants are in poor soil, you can get away with a one-time application of granular fertilizer in the spring. Of course, there are exceptions.

Some perennials are “heavy feeders” and thus require more food, or fertilizer. Heavy-feeding perennials are as follows:

  • Mums
  • Lupines
  • Lilies
  • Peonies
  • Delphiniums
  • Astilbe
  • Tall phlox

On the flipside, there are also perennial plants that don’t need fertilizer. Below are the perennials that do best without fertilizer supplements:

When to fertilize

Since most of your perennials likely won’t need much fertilizer to survive and thrive, it’s best to pay attention to the suggested fertilizing times. Remember, the only perennials that will benefit from fertilizers are the heavy feeders and those planted in sandy soil or soil without many organic nutrients. Leave your perennial alone if it’s planted in rich soil and seems to be doing well!

If you’re wondering when to fertilize the perennials that do need a little boost, here’s what Michigan State University Extension says:

Perennials may benefit from a fertilizer application before or at the time that new spring growth is pushing up. The most common recommendation is to apply no more than 1 pound of nitrogen per 1,000 square feet if no compost is used. (For comparison, this is about one-fourth of what you would apply to your lawn during a growing season.)

So, again, don’t overdo it, and you should be alright. It is also suggested that correct yearly composting can eliminate the need for extra fertilization of perennials altogether. As for the heavy feeding perennials, you can feed them in the spring, then again in the summer with other spot liquid treatment or “side-dressing,” which means spreading several tablespoons of fast-release fertilizer in the general root area of the plant. Don’t fertilize the crown, though—this can burn the plant.

Do not fertilize perennials in the late summer or fall. It can promote additional growth that won’t have enough time to stabilize before the winter.

Think you can handle fertilizing your perennials? Hopefully we cleared up some questions for you! For more helpful gardening tips that will help you keep your plants alive, join Rozanne’s Inner Circle.

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