How Often Should You Fertilize Your Plants? We Asked Garden Experts

Plants need a certain amount of specific nutrients to grow well. Most of the time, garden and houseplants do fine without any help from you. But fertilizing actually gives plants a boost that helps them flourish. “Photosynthesis is how plants make food,” says Stacey Hirvela, horticulturalist with Spring Meadow Nursery and Proven Winners Color Choice Shrubs. “But fertilizer is like giving them vitamins.”

Fertilizing your plants keeps them strong and able to stand up to whatever nature throws at them during the growing season. “The best defense against pests and diseases is a healthy plant,” says Hirvela. “When growing vigorously, a plant can outpace pests and diseases and are naturally more resilient to various environmental stressors.”

Before you fertilize, it’s also a good idea to do a soil test of your garden or landscape beds to identify what nutrients are lacking—or those nutrients of which you have an excess amount. Your local university coop extension service can help (find yours here). 

Do You Have To Fertilize Plants?

Most residential soils contain the nutrients plants need to sustain healthy growth, and you can have a beautiful landscape filled with perennials, shrubs, and trees without fertilizing. “But when you fertilize, you add additional nutrients that the plant can funnel into bigger, more abundant flowers, faster growth, or darker foliage,” says Hirvela.

Houseplants also benefit from fertilizer. “If you’ve had a plant in the same pot for five years, it’s probably a good idea to fertilize,” says Justin Hancock, horticulturalist with Costa Farms. “You can get away with never fertilizing, but a plant will perform better with some level of fertilizer.”

In your vegetable garden, plants grow fast and consume lots of nutrients as they produce flowers and fruit, so they benefit from  frequent feeding. “Heavy feeders are the veggies that need more nutrients to perform well,” says Josh Kirschenbaum, vegetable business and portfolio manager, PanAmerican Seed Company. “Examples include corn, peppers, squash, and tomatoes.”

How Often Should You Fertilize Perennials, Shrubs, And Trees?

For most established perennials, shrubs, and trees, you can fertilize with slow-release granular fertilizer once a year in late winter to early spring. “Sustained-release products encourage slower, more sustained growth with the nutrients available over a longer period of time,” says Hirvela. You’ll also have a better sense of how much you’re using. However, liquid fertilizer is okay, too, if you prefer to use it throughout the season.

Regardless of the type used, stop by late summer (mid to late August) in hot climates or by the end of July in cooler climates. This is because you don’t want to push soft, tender growth too late in the season because it won’t have time to harden off, so it will be damaged by the cold. “It’s a waste of a plant’s energy and your money to encourage new growth too late in the season,” says Hirvela.

How Often Should You Fertilize Houseplants?

Houseplants can benefit from any fertilization schedule. In fact, fertilizing is especially helpful for houseplants because outdoors, there’s a regenerative process, with organic matter being regularly added back to the soil from sources such as dying insects, leaf litter and so on. That obviously doesn’t happen indoors, says Hancock.

Either slow-release granular that lasts a few months or a liquid fertilizer is fine. “But less is more,” says Hancock. “The label lists the maximum amount you should use, but you can use any amount less than what’s recommended. Just don’t use more than the label indicates or you can burn the roots and harm your plant.”

How Often Should You Fertilize Vegetable Gardens?

Place a granular slow-release vegetable fertilizer in the hole at planting time. “But fruiting crops like tomatoes and peppers also benefit if you ‘side dress’ them, or sprinkle a bit of fertilizer at the base of the plant when they are flowering to promote larger harvests,” says Kirschenbaum. Liquid fertilizers also can be used throughout the season, especially if the plant looks a bit weak or its foliage is light green in color.

 Vegetables grown in pots typically need to be fertilized more frequently than veggies in ground. This is because every time the plants are watered, there’s a potential for fertilizer to wash out of the pot. “Keep an eye on how healthy the plant looks, which will give you an indication of when it needs more fertilizer,” says Kirschenbaum.

What Type Of Fertilizer Should You Use?

Most of the time, you can use any general-purpose fertilizer for perennials, shrubs, and trees. “Don’t worry too much about using the ‘right’ kind of fertilizer,” says Hirvela “You don’t need a ‘spice rack’ full of different types of fertilizers for every type of plant. Use what you have.”

For vegetables, choose a fertilizer that’s labeled for vegetables or that has a relatively low NPK ratio, such as 12-10-5, says Kirschenbaum.

For the majority of houseplants, any general-purpose houseplant fertilizer will do. “The only exception is orchids, which are epiphytic so they have different nutrient needs. Choose a product formulated specifically for them,” says Hancock.