Plant Fertilizer 101: How to Feed Your Garden

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Strong and healthy plants thrive when you feed them properly. Here’s how to give your garden a nutrient boost with plant fertilizer.

Farmer Giving Granulated Fertilizer To Young Tomato PlantsZBYNEK POSPISIL/GETTY IMAGES
A gardener applies granulated fertilizer to young tomato plants

Shopping for plant fertilizer and applying it may seem perplexing at first. Follow these simple tips and you’ll be fertilizing like a pro in no time.

Read the Label

plant fertilizer bagVia Merchant
The numbers on a fertilizer package represent nitrogen, phosphorus and potassium.

The front of every bag contains three numbers, such as 10-10-10 or 10-15-10 or 6-3-0. In order, these represent the percentage of nitrogen, phosphorus in the form of phosphate, and potassium in the form of potash. The rest of the material is filler that dilutes the fertilizer so it’s easier to apply. A balanced fertilizer (formulation 10-10-10 or 12-12-12) may seem suitable for most gardens, but this can lead to excessive levels of phosphorus and potassium, so it’s important to conduct a soil test before choosing a fertilizer.

Many are also labeled as fast- or slow-release, indicating how quickly the nutrients are available to the plant. Fast-release types dissolve in water and are readily available. They are fast-acting and less expensive but pose a greater risk of fertilizer burn and groundwater pollution if misapplied.

Slow-release types deliver small amounts of nutrients for plants to use over time. They have a lower burn potential and require fewer applications, but usually cost more.

Avoid these common mistakes you’re making with your tomato garden.

How to Apply Plant Fertilizer

Fertilizer pellets spraying from spreaderBanksPhotos/Getty Images
Apply fertilizer granules to large areas with a spreader.

Drop and broadcast spreaders apply granular fertilizer to large spaces, such as established grassy areas or unplanted large lawns, beds and gardens. In existing gardens, apply when the plants are dry. Brush off any granules that land on leaves. Lightly cultivate and then water, so the fertilizer soaks into the soil.

Use hand-held spreaders for applying granular fertilizer to small or medium-sized gardens. With this technique, fertilize only the plants that need it. Sprinkle on the ground around the base of plants and lightly scratch into the soil with a rake or trowel. Unless steady rain is predicted, water right away.

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How Often to Fertilize Plants

Hand Holding Shovel Full of Compost, Home CompostingOnfokus/Getty Images
Apply compost to feed your perennials in spring.

Annuals

Annual plants should be given a low-nitrogen formula. Use 2 to 3 pounds per 100 square feet every season. Use a slow-release fertilizer once, or make three 1-pound applications throughout the growing season. In areas with a long season, a midseason application may be needed.

Ground Covers

Most ground covers need only one spring application of nitrogen-rich fertilizer, but those with flowers and fall color typically don’t.

Perennials

Perennial plants perform best when fertilized in spring with compost or aged manure. Apply 2 inches every two to three years, using additional fertilizer as needed.

Container Plants

For potted plants, add a slow-release type to the soil mix before planting. Every time you water, a little fertilizer is released, providing a steady flow of nutrients. But depending on the growing conditions and number of plants in the container, a midseason boost may be needed. Can you reuse potting soil in planters?

Trees and Shrubs

Avoid over fertilizing trees and shrubs, which often get nutrients from nearby fertilized plantings and lawns.

Learn the 7 things you need to know before planting a tree.

Signs of Nutrient Deficiencies

Calcium deficiency on a tomatoMiyuki-3/Getty Images
Blossom end rot is a sign of calcium deficiency in tomatoes
  • Nitrogen: Pale green or yellowish lower leaves; slow growth.
  • Potassium: Yellow or brown along older leaf edges. May have yellowing between veins, curling or spotting.
  • Calcium: Deformed or failed terminal buds and root tips. Results in blossom end rot in peppers and tomatoes.
  • Phosphorus: A burned look on leaf tips; dark green or reddish purple older leaves.
  • Sulfur: Light green over the entire plant; yellowing of younger leaves.
  • Iron: Yellowing between veins of upper leaves leading to an eventual bleached look. Possibility of new leaves being yellowish white.
  • Manganese: Paling or yellowing of leaf tissue between veins, followed by spots that occur on middle leaves first

Keep a Record

spring flat lay with notebook, gardening tools and glovesCentralITAlliance/Getty Images
Write down the date when you apply fertilizer to make sure you don’t feed your plants too often.

Stay on top of your plant fertilizer applications by making notes on a calendar.

Next, find out if you should use coffee grounds in the garden.

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Kirsten Schrader
Kirsten is the content director of Birds & Blooms. She's been with the brand in various roles since 2007. She has many favorite birds (it changes with the seasons), but top picks include the red-headed woodpecker, Baltimore oriole and rose-breasted grosbeak. Her bucket list bird is the painted bunting.