Everything You Need to Know About Fertilizing Your Plants

susan martin |  june 28, 2023

Some of the questions we hear most often from our customers at Garden Crossings are centered around fertilizing plants. What kind of fertilizer is best? How much and how often should I feed my plants? We’ll do our best to answer those questions here.

 

First, a little background.

 

What’s the difference between feeding and fertilizing? For our purposes here, the two words mean the same thing. They both refer to providing your plants with the nutrients they need to thrive. 

The three main nutrients that general fertilizers provide are nitrogen (N), phosphorus (P) and potassium (K). Nitrogen benefits the plants’ foliage and turns it an attractive, deep green color. Phosphorus helps the plants’ roots grow and stimulates flower and fruit production. Potassium (also known as potash) supports the overall good health and strength of the plant. 

 

When you read a fertilizer package, you’ll see the N-P-K ratio stated there in numerical terms. The numbers indicate the percentage of each nutrient present in the product by weight. In the example above of Espoma’s Plant-tone® fertilizer, the ratio stated at the top is 5-3-3.

 

What’s known as “balanced fertilizers” have equal numbers such as 10-10-10. Those designed to make flowers bloom more heavily will have a larger middle number like 10-30-20. The number zero indicates there is none of that nutrient included in the product.

 

Some fertilizers also include macronutrients that plants need such as iron, sulfur, magnesium and calcium. Iron is not easily absorbed by plants unless the soil’s pH is just right or unless it is in a special form known as EDDHA iron. Proven Winners’ water soluble plant food contains this form of iron, which is why the water turns brown when you mix the product up. It’s one of the reasons why this brand of plant food is more effective than cheaper water soluble fertilizers. 

Don’t plants make their own food?

If you think back to elementary school science class, you may recall your lesson on photosynthesis. It’s the process by which plants make their own food using the chlorophyll in their leaves to turn sunlight into energy. It happens even when plants are growing in the shade or indoors. This is the basic energy all plants need to survive.

 

Beyond that, plants require 17 essential elements to grow and develop properly. Three of them—carbon, hydrogen and oxygen—are drawn from air and water. The rest are taken up by the plants’ roots from the soil. If a plant cannot absorb those nutrients from the soil, either because they aren’t present or because the properties of the soil limit absorption, you can often tell because the plant starts to look unhealthy. Its leaves might start to turn yellow, or its growth might be slow or stunted. 

How can I tell what’s in my soil?

How do you know if your soil has all the essential elements to help plants grow? The best way to know for sure is to have a soil test done. This is a very simple process. Visit your local County Extension Office’s website to order a soil testing kit. They will ask you to spoon a bit of soil from different parts of your yard into the provided box and mail it back to their office.

 

In exchange for a small fee, they will send you a complete soil report in return. This report will help you understand exactly which nutrients are in your soil, so you’ll know what you need to add and what you don’t. Soil tests can be done every few years and should be performed early on when you are starting a brand new garden. If you skip this step, you could risk adding too much or not enough of the right nutrients to your soil.

What should I use to feed my plants?

There are several variables to this question, but the primary one is knowing which kinds of plants you are trying to feed. Are they trees, shrubs, roses, hydrangeas, perennials, annuals, bulbs or houseplants? Is your plant an acid-loving type? Different kinds of plants prefer different kinds of fertilizers.

 

We carry a full line of Espoma organic plant foods and soil building ingredients. This comprehensive article explains all of the Espoma products we carry so you’ll know which product is best for each type of plant. We also offer Proven Winners’ water soluble and continuous release plant foods.

 

Fertilizers come in both granular and liquid or water soluble forms. The granular types are designed to feed your plants a little bit at a time over an extended period. The liquid or water soluble types are meant to give your plant a quick fix of nutrients that it will absorb all at once. Think of granular fertilizer as insurance. It provides a low level supply of nutrients all the time. Liquid fertilizer is a quick “meal” for your plants – nutritious but not long-acting.

Many annuals, especially prolifically flowering annuals like petunias, calibrachoa and bedding impatiens, grow best if you feed them with both granular and liquid fertilizers. By contrast, most perennials and shrubs only need one application of granular fertilizer in the spring for sufficient growth. Young trees can benefit from being fed in the spring, too. Tree fertilizer comes in several different forms, from spikes to granular to injectable liquid.  

 

Compost, soil conditioner, earthworm castings, shredded leaves, pine straw and grass clippings can be used to add organic matter to your soil. They are all great long-acting materials that will work over the years to enrich your soil slowly as they decompose. They are especially important where the soil is poor or low in nutrients such as in sandy soils, heavy clay, and new construction fill dirt. Slow release granular and liquid fertilizers can be used along with these organic items to build up the nutrients in your soil.

Acid-loving plants such as azaleas, rhododendrons, hydrangeas, hollies, camellias and conifers benefit from being fed with a special fertilizer called Holly-tone® by Espoma in the spring. It’s important to realize that this is only fertilizer and is not the same product that is used to make the soil more acidic to turn hydrangeas blue. That product is called Soil Acidifier. Both Holly-tone and Soil Acidifier can be applied to the same plant without harming it. If your soil’s pH is neutral or alkaline, Soil Acidifier helps to make it more acidic so that the acid-loving plants can better absorb the fertilizer. Both products are slow acting and will take time to have an effect.

How often should I feed my plants?

How often you should feed your plants is dependent on several factors including:

  • What kind of plant is it?
  • Is it growing in the ground or in a container?
  • If in the ground, do you have heavier soil like clay or light soil like sand?
  • Are you looking to maximize your plant’s performance or to feed it just enough for it to survive?

Annuals, meaning plants that complete their life cycle in one year, tend to be much “hungrier” plants than perennials, shrubs and trees. Flowering annuals often produce fewer flowers or stop flowering altogether when they run out of nutrients, so they need to be fed more often. Perennials and shrubs tend to bloom at one specific time of the year and usually can draw enough nutrients from the soil to complete that bloom cycle. 

 

Plants growing in the ground have a greater reserve of nutrients and moisture to draw from the earth. Their roots can spread wider to seek what they need. Heavier soils like clay or amended clay bind nutrients more tightly, so they don’t flush down through it as quickly as they do in loose, sandy soils.

 

Plants growing in containers have a finite amount of soil from which to draw nutrients and moisture. Their roots are limited to the container and can’t seek what they need outside of those walls. Each time it rains or you water, a tiny amount of nutrients is washed out of the drainage hole. Heavy thunderstorms can deplete the nutrients out of containers fairly quickly, which is why it’s a good idea to fertilize after a series of heavy rains.

When should I feed my plants?

Annuals growing in containers, especially flowering annuals, require the most frequent fertilizing of any plants. We recommend feeding them every third time you water or once per week for maximum plant performance. If you wait to feed just once per month and your annuals go out of bloom in the meantime, it can take a couple of weeks for them to start blooming normally again after feeding with water soluble or liquid plant food.

 

Most perennials, shrubs and new trees growing in the ground can be fed with a slow acting granular plant food once per year in the spring when they start to wake up from their winter’s slumber. Perennials and shrubs that are heavier feeders, such as roses, reblooming hydrangeas, tall garden phlox and irises, can benefit from being fed a second time in early summer. Mature trees that are growing near your lawn will absorb the nutrients from your turf fertilizer. Where there isn’t lawn, the leaves that fall from deciduous trees in the fall eventually decompose and provide the essential nutrients the trees need to prosper.

 

It’s not a good idea to fertilize trees and shrubs from midsummer through mid-fall. That’s because doing so would likely prompt tender new growth which would not have enough time to harden off before winter. Late feeding can also interfere with a plant’s natural dormancy process and can result in winter damage.

How Much Should I Feed My Plants?

It is important to follow the package instructions when you are using fertilizer. Read each package, as the rates will vary with each one. Think of it like baking a cake. Too much of one ingredient can ruin the whole cake, but following the directions will deliver good results every time.

 

Take care not to over-feed your plants. Not only will you be wasting your money, but you can also harm your plants and contaminate your water resources with excess fertilizer. The amounts stated on the package have been tested and proven to work. You don’t need any more to benefit your plants.

 

If you are broadcasting fertilizer over a large area, a drop spreader will come in handy. The number for which to set your spreader should be printed on the back of the package of fertilizer. To treat smaller areas or individual plants, you’ll want to have a dedicated set of measuring cups and tablespoons that you use only for this purpose.

It’s always a good idea to wear gloves when you are mixing up and applying fertilizer. Don’t spray on windy days if you can avoid it. Be sure you are standing up-wind when you spray any garden products to avoid getting them on you. Also, take care to store fertilizers properly according to package instructions and keep them out of the reach of children and pets.

 

Remember that you should not expect to see instant results from granular and slow release fertilizers. Those products are designed to aide your plants over a period of many weeks and months. You’ll notice results faster when you use liquid and water soluble fertilizers, but they will need to be applied more often.

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