Fertilizing in the Home Garden

fertilizing strawberries
Many plants benefit from regular fertilization.  (1)

Many areas of the landscape benefit from fertilization, especially the lawn, edible gardens, flowering annuals, and houseplants.  However, figuring out how and when to use fertilizers responsibly can be confusing, and improper fertilization can harm plants and the environment.  

Follow the guidelines below to learn more about fertilizing all the plants in your landscape and garden properly.


Basics  |  Types  |  Applying Fertilizers  |  Fertilizer Requirements  |  FAQs  |  More Information 


Fertilizer Basics

All plants require 17 essential mineral nutrients to grow and complete their life cycle.  These nutrients are made available to the plant from the soil.  Some of these nutrients, like nitrogen, phosphorous, and potassium, are used in large quantities. Others, such as iron, boron, and manganese, are needed in very small quantities.  The table below lists all the mineral nutrients essential for plant growth.

As plants grow, they utilize these nutrients in the soil, and if they are not replaced, growth can slow, or plants can become unhealthy.  To provide the best growth possible, many plants benefit from fertilizer applications.

MacronutrientsMicronutrients
Needed in relatively large quantitiesNeeded in relatively small quantities
  • Nitrogen (N)
  • Phosphorus (P)
  • Potassium (K)
  • Sulfur (S)
  • Calcium (Ca)
  • Magnesium (Mg)
  • Iron (Fe)
  • Manganese (Mn)
  • Zinc (Zn)
  • Copper (Cu)
  • Boron (B)
  • Molybdenum (Mo)
  • Nickel (Ni)
  • Chlorine (Cl)

Because macronutrients are used in large quantities, they are the most important nutrients to consider when applying fertilizers, as they are the most likely to be deficient in the soil.  

Most Iowa soils contain sufficient amounts of micronutrients; additional supplementation is rarely needed. Many commonly used commercial fertilizers, and even things like compost and animal manure, contain micronutrients as impurities.

Fertilizer Analysis

The series of three numbers on a fertilizer package indicate the amounts or percentages of nitrogen, phosphate, and potash in the fertilizer.  These three nutrients are the most used by plants and, as a result, are often limiting to the growth and health of plants in the garden.  

The first number refers to the percentage of the fertilizer's weight is nitrogen.  The second (middle) number gives the percentage of phosphate (which contains phosphorous), and the third refers to the amount of potash (which contains potassium). For example, a  fertilizer analysis of 10-6-4 contains approximately 10% nitrogen, 6% phosphate, and 4% potash. 


Types of Fertilizers

store shelves with fertilizer
There are many types of fertilizers available.  General-purpose (or all-purpose) fertilizers are suitable for a wide range of plants in the landscape. (2)

Deciding what type of fertilizer to use can be a bit confusing.  Look at the fertilizer label first.  Fertilizer labels often tell you the type of plant it was formulated for.  For example, if it is an orchid fertilizer, this will often be prominent on the label.  Lawn fertilizers generally contain high nitrogen levels (first number) to promote vegetative or leafy growth. Lawn fertilizers are great for your grass, but lousy for annual flowers (too much nitrogen promotes excessive vegetative growth and inhibits flowering).  

General-purpose fertilizers are often complete (contain nitrogen, phosphate, potash, and other macro- and micronutrients) and are suitable for a wide range of plants in the garden, landscape, or containers. In the label directions, you will often get information on different application rates for different groups of plants.

Forms of Fertilizers

Home gardeners commonly use granular or liquid forms of fertilizer.  Granular fertilizers can be water soluble (fast dissolving) or slow-release materials.  Slow-release fertilizers are formulated to release nutrients slowly over several weeks or months, so one application in spring may be all that is necessary.  Liquid fertilizers are fast-acting and can be added to the water you use to irrigate your plants.

Organic vs. Synthetic Fertilizers

From a plant perspective, both organic and synthetic fertilizer sources can supply the nutrients needed.  There are pros and cons to both types of fertilizers. Organic fertilizers are often lower in analysis (less nitrogen, phosphorus, potassium, etc.), making them less likely to cause injury due to over-application.  Yet, this lower analysis may mean applying more product in poor soils.  Organic fertilizers may not supply specific nutrients, while synthetic formulations can include many macro- and micro-nutrients.  However, organic fertilizers, like composted manures, can also improve soil quality over time, unlike synthetic fertilizers. 

Depending on the situation, many gardeners will use both organic and synthetic fertilizers.  For example, some gardeners will add composted manure to the vegetable garden in fall to improve soils and then still add granular synthetic fertilizers as a top dressing after planting for long-season vegetables like tomatoes.

Compost

coompost
Compost is a good supplement for fertilizer, but rarely has enough nutrients to replace other fertilizers (3)

To a limited extent, compost is a source of nutrients. However, nutrient release from compost is slow, and the nutrient content is often too low to supply all the nutrients necessary for plant growth. Compost should not be considered a substitute for fertilizer but rather a supplement. Compost increases the ability of the soil to hold and release essential plant nutrients, especially in sandy soils. This may reduce the amount of fertilizers needed.

Learn more about compost in this article: Composting FAQs.

Manures

Manure is the oldest fertilizer known to civilization and can be a cost-effective soil amendment with many beneficial qualities. Careful and appropriate use of manure, especially in vegetable gardens, is important. Certain precautions should be taken to prevent potential problems with the transmission of food-borne illnesses from manure contamination. 

Using well-composted manure rather than fresh can lower the risks involved with using manure. Composting the manure reduces the odor and weight and kills many weed seeds and pathogens (as long as the pile gets to 131°F or higher).

Fall applications of composted manure are best because edible crops should not be harvested until 90 or 120 days after a manure application (90 days for edible crops not in contact with the ground and 120 for those that do contact the soil).

Learn more about safely and effectively using manure in the garden in this article: Using Manure in the Home Garden.

Foliar Fertilizers

Some specialty fertilizers are promoted for foliar application. The claim is that the nutrients are readily available to the plant by absorption through leaf surfaces. This practice has more disadvantages than advantages for the homeowner. Usually, less than five percent of the total nutrients enter the plant, and this is not enough to make a difference in plant growth. Further, the risk of plant damage is high from salt burn, especially when applied in temperatures above 80°F or when humidity levels are low. 

Maintaining plant health through nutrient application is best done through a sound soil-applied fertilizer program based on soil test results.


Applying Fertilizers

apply fertilizer around rose bush
The rate and frequency of application depends on many factors. (4)

The rate and frequency of application depends on the nutrient analysis of the fertilizer, plant species, soil type, and other environmental factors.  Always start with a soil test to determine the amount of fertilizer needed.  

Learn more about collecting and submitting a soil test in this article: Soil Testing Resources for Home Gardeners.

Can you fertilize too much?

Yes, over-fertilization can burn plant leaves, stunt growth, and create environmental issues.  More is rarely better when using fertilizers.  Always read and follow label recommendations for fertilizer rates, dilutions, and application guidelines.  If you are ever in doubt, always err on the conservative side or use less fertilizer.

Tips for Applying Fertilizers

  • ALWAYS read and follow label directions before applying any fertilizer.
  • Avoid applying fertilizers when the soil is dry. (This increases the chances of burning the foliage.)
  • Newly planted trees, shrubs, and perennials rarely need fertilizer during the first growing season.  (Regular water applications to aid in root establishment are more important.)
  • For container plants in potting soil (soilless media), regular fertilizer is important when the plant is growing. If you use liquid or water-soluble fertilizers, avoid fertilizing every time you water.   

Fertilizer Requirements

Not all plantings in the home landscape require the same amount of fertilizer.  Some areas, like the lawn, need frequent applications and other plantings, such as shade trees and ornamental shrubs, rarely, if ever, need supplemental fertilizer. 

These are all general recommendations and could vary, so watch your plants.  Poor or slow growth and overall yellowing are signs that a plant may be lacking essential plant nutrients and would benefit from an application of fertilizer.


Vegetables  |  Small Fruits  |  Fruit Trees  |  Perennials  |  Annuals  |  Bulbs  |  Roses  |  Trees & Shrubs  |  Lawns  |  Houseplants


Vegetables

applying granular fertilizer in vegetable garden
Slow release fertilizers can be spread in the root zone of the plant to provide nutrients over several weeks or months (5)

Vegetables require regular fertilizer applications for high-quality vegetables and good yields.  Some crops require relatively high amounts of fertilizer (sweet corn, garlic, etc.).  Other crops produce well with fewer fertilizer applications (lettuce, herbs, etc.).  Many gardeners use compost along with organic and/or synthetic fertilizers incorporated into the soil before planting (and for some vegetables, during the growing season as well).  

Small Fruits

Like vegetables, small fruits like strawberries and raspberries require regular fertilization for good yields and high-quality fruit. 

More information can be found in this article: Fertilizing Tree and Small Fruits in the Home Garden.

Fruit Trees

It is generally not necessary to fertilize fruit trees in Iowa.  Most Iowa soils can supply sufficient amounts of nutrients to fruit trees.  Fruit trees with less than desirable growth may need fertilizer applied in early spring.  

Learn more in this article: Should I fertilize my fruit trees?

Perennials

For most perennials, applying 1 to 2 pounds of an all-purpose garden fertilizer per 100 square feet in early spring is adequate. 

Learn more in this article: How often should I fertilize perennials?

Annuals

water soluble fertilizers
Water soluble fertilizers are convenient for annuals and houseplants (6)

Annuals benefit from regular fertilizer applications throughout the growing season.  Slow-release or water-soluble fertilizers can be used. 

Plants in containers need to be fertilized regularly as nutrient levels in potting mixes quickly fall due to absorption by plants and leaching during watering.  Many commercial potting mixes contain a slow-release fertilizer.  However, slow-release fertilizers seldom last the entire growing season.       

Bulbs

While not typically necessary, fertilizers can be used at bulb planting. These fertilizers are more important for developing next year's bulb than the upcoming spring flowers.  

Established bulb plantings should be fertilized after blooms fade.  Two to three pounds of a 5-10-5 or similar analysis fertilizer may be applied to 100 square feet of bed area. 

Learn more in this article: Selecting and Planting Spring Blooming Bulbs.

Roses

Shrub roses can be fertilized in early spring with an all-purpose garden fertilizer.  Hybrid Teas and other modern roses benefit from several applications throughout the growing season.  

Apply fertilizer around the base of the plant in a band 18 inches wide, approximately 6 inches out from the base of the canes.  Lightly incorporate it in the soil.  

Learn more in this article: Growing Roses in Iowa.

Trees and Shrubs

It is generally not necessary to fertilize healthy, vigorous trees and shrubs in the home landscape.  Most landscape soils in Iowa contain adequate levels of nutrients for trees and shrubs. Spring and fall are the best times to fertilize trees and shrubs if necessary.  

Learn more in this article: Should I fertilize established trees and shrubs?

Lawns

fertilizing the lawn
When fertilizing lawns, use a fertilizer formulated for use on turfgrass.  They have high amounts of nitrogen compared to other components (7)

In Iowa, lawns can be fertilized in late October/early November, mid-September, and spring (April or May).  

The number of fertilizer applications is primarily determined by an individual's desires or expectations for their lawn.  A single fertilizer application in late October/early November would be sufficient for individuals who prefer minimal fertilization.  A moderate fertilization plan consists of both fall applications. All three applications would be appropriate for individuals who want a vigorous, dark green lawn.  

Each fertilizer application should consist of one pound of actual nitrogen per 1,000 square feet using a fertilizer formulated for lawns which will have high amounts of nitrogen (the first number in the fertilizer analysis) compared to the other components.  

Learn more in this publication: Lawn Fertilization.

Houseplants

Fertilize indoor plants while actively growing (typically in spring and summer).  

You can buy fertilizers specially formulated for houseplants or utilize balanced, all-purpose fertilizers.  When using general, all-purpose fertilizers, mix them at half or quarter the strength outlined in the instructions because houseplants grow slower than the outdoor plants the instructions are written for.  

Learn more in this article: How to Care for Houseplants.


Fertilizer Frequently Asked Questions

My plant looks sick. Should I fertilize it?

First, you must figure out why the plant is not doing well.  Ask yourself the following questions: "Has it been over-watered or under-watered?  Is it receiving enough light or too little light?  Are there signs of disease or other pests?" before pulling out the fertilizer bag.  Fertilizer doesn't fix all problems and in some situations, it can make the problem worse.

Why are some fertilizers blue or pink?

Dyes (usually blue) are added to some fertilizers to identify them as a fertilizer and so that you can loosely determine how much you are applying.  As you would expect, a dark blue solution contains higher amounts of nutrients than a light blue solution.

Are fertilizers harmful to pets or kids?

Fertilizers, like many other household chemicals, have the potential to harm people and animals when misused or consumed.  They should be kept out of the reach of children and pets.  


More Information


Photo credits: 1: bildlove/AdobeStock; 2: murdocksimages/AdobeStock; 3: SUPHANSA/AdobeStock; 4: Julia/AdobeStock; 5: encierro/AdobeStock; 6: ronstik/AdobeStock; 7: The Toidi/AdobeStock

Last reviewed:
June 2024