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 nutrients and would benefit from fertilizer.
Vegetables | Small Fruits | Fruit Trees | Perennials, Annuals, & Bulbs | Roses | Trees & Shrubs | Lawns | Houseplants
Vegetables
Vegetables require regular fertilizer applications for high-quality vegetables and good yields. Some crops require relatively high levels of fertilizer (e.g., sweet corn, garlic). 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).
More information on rates for various vegetable crops can be found in this article: Vegetable Growing Guides.
A soil test will provide information to determine recommended fertilizer rates. The tables below provide general recommendations for fertilizer rates in the vegetable garden based on soil test results.
| Soil Organic Matter Percentage | Amount of Nitrogen to Apply* (lbs/100ft2) |
|---|---|
| Less than 3% | 0.20 |
| Between 3% and 19% | 0.15 |
| More than 19% | 0.10 |
| Phosphorous Soil Test Level (ppm) Bray-P1 Test** | Phosphorous Soil Test Level (ppm) Olsen-P Test** | Amount of Phosphate to Apply* (lbs/100ft2) |
|---|---|---|
| 0-5 | 0-3 | 0.40 |
| 6-10 | 4-7 | 0.30 |
| 11-15 | 8-11 | 0.20 |
| 16-25 | 12-18 | 0.10 |
| 25+ | 18+ | 0.00 |
| Potassium Soil Test Level (ppm) | Amount of Potash to Apply* (lbs/100ft2) |
|---|---|
| 0-50 | 0.40 |
| 51-100 | 0.30 |
| 101-150 | 0.20 |
| 151-200 | 0.10 |
| 200+ | 0.00 |
*The amount of nutrients to apply does not equal the amount of fertilizer to apply. To determine fertilizer amounts, consult this article: How to Calculate Fertilizer Rates for Lawn and Garden
**Phosphorous is tested in two different ways depending on soil pH. Select the appropriate rate based on the test used.
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 nutrients for 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, Annuals, and Bulbs
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
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 decline quickly due to plant uptake 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 the time of bulb planting. These fertilizers are more important for developing next year's bulbs than the upcoming spring flowers.
Established bulb plantings can be fertilized either just as the new growth emerges in the spring or after blooms fade (but not both). Two to three pounds of a 5-10-5 or similar analysis fertilizer should be applied to 100 square feet of bed area. Fertilizer is not needed for bulb plantings not intended to be in the garden year after year (such as hybrid tulips that are replaced each fall).
Learn more in this article: Selecting and Planting Spring Blooming Bulbs.
Fertilizer Recommendations Based on Soil Test Results
| Soil Organic Matter Percentage | Amount of Nitrogen to Apply* (lbs/100ft2) |
|---|---|
| Less than 3% | 0.20 |
| Between 3% and 19% | 0.15 |
| More than 19% | 0.10 |
| Phosphorous Soil Test Level (ppm) Bray-P1 Test** | Phosphorous Soil Test Level (ppm) Olsen-P Test** | Amount of Phosphate to Apply* (lbs/100ft2) |
|---|---|---|
| 0-5 | 0-3 | 0.40 |
| 6-10 | 4-7 | 0.30 |
| 11-15 | 8-11 | 0.20 |
| 16-25 | 12-18 | 0.10 |
| 25+ | 18+ | 0.00 |
| Potassium Soil Test Level (ppm) | Amount of Potash to Apply* (lbs/100ft2) |
|---|---|
| 0-50 | 0.40 |
| 51-100 | 0.30 |
| 101-150 | 0.20 |
| 151-200 | 0.10 |
| 200+ | 0.00 |
*The amount of nutrients to apply does not equal the amount of fertilizer to apply. To determine fertilizer amounts, consult this article: How to Calculate Fertilizer Rates for Lawn and Garden
**Phosphorous is tested in two different ways depending on soil pH. Select the appropriate rate based on the test used.
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.
If a soil test shows fertilization is needed, spring and fall are the best times to fertilize woody plants.
The soil test will provide information to determine recommended fertilizer rates. The tables below provide general recommendations for fertilizer rates of newly planted and established trees and shrubs.
| Soil Organic Matter Percentage | Amount of Nitrogen to Apply* (lbs/100ft2) |
|---|---|
| Less than 3% | 0.10 |
| Between 3% and 19% | 0.07 |
| More than 19% | 0.05 |
| Phosphorous Soil Test Level (ppm) Bray-P1 Test** | Phosphorous Soil Test Level (ppm) Olsen-P Test** | Amount of Phosphate to Apply* (lbs/100ft2) |
|---|---|---|
| 0-5 | 0-3 | 0.20 |
| 6-10 | 4-7 | 0.10 |
| 11-25 | 8-18 | 0.05 |
| 25+ | 18+ | 0.00 |
| Potassium Soil Test Level (ppm) | Amount of Potash to Apply* (lbs/100ft2) |
|---|---|
| 0-50 | 0.20 |
| 51-100 | 0.10 |
| 101-150 | 0.05 |
| 150+ | 0.00 |
*The amount of nutrients to apply does not equal the amount of fertilizer to apply. To determine fertilizer amounts, consult this article: How to Calculate Fertilizer Rates for Lawn and Garden
**Phosphorous is tested in two different ways depending on soil pH. Select the appropriate rate based on the test used.
Learn more in this article: Should I fertilize established trees and shrubs?
Lawns
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 lawn-care preferences or expectations. 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 seeking a vigorous, dark-green lawn.
Each fertilizer application should consist of 1 pound of actual nitrogen per 1,000 square feet, using a lawn fertilizer with a high nitrogen content (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.
More Information
- Fertilizing in the Home Garden
- How to Calculate Fertilizer Rates for Lawn and Garden
- Natural (Organic) Fertilization for Turf (PDF)
- Managing Garden Soil.
- Garden Soil Management (PDF)
- Composting Yard Waste (PDF)
Photo credits: 1: Khaligo/AdobeStock; 2: ronstik/AdobeStock; 3: The Toidi/AdobeStock