When to Stop Fertilizing Your Garden for the Year, According to Horticulturalists

When it comes to adding fertilizer to your garden, the key is to know exactly what nutrients are already in your soil. In many cases, you likely won't need to fertilize more than once a season—though in the case of vegetable gardens with heavy feeders, you may be fertilizing multiple times. But when is the right time during the season to stop feeding your plants? We spoke to plant experts who explain when is the best to stop fertilizing perennial, edible, and deciduous plants, plus when you should refrain from fertilizing in the first place.

Why Stop Fertilizing Your Plants?

Fertilizing your plants means giving them nutrients to continue growing. But, there comes a point in most plants' lifecycles when they need to prepare to go dormant or die off for the season. In this case, it's actually harmful to the plant to continue feeding it. Fertilizers generally contain nitrogen, which encourages new, leafy, vegetative growth when absorbed by your plants. But that new, young growth could be at risk of cold damage if it's grown too late into the year and closer to your region's first frost date.

When to Stop Fertilizing Perennials

Once you see your plants in bloom, stop fertilizing, says Laura Irish-Hanson, a horticulture educator at the University of Minnesota Extension. And definitely stop feeding them by the time fall comes, says Charlotte Glen, a master gardener from the Department of Horticultural Science at North Carolina State University. "I would not fertilize perennials late in the fall because the plant is trying to go dormant," says Glen. With the late addition of fertilizer, a perennial may think it's time to keep growing, and any new growth likely won't survive a hard frost.

When to Stop Fertilizing Edible Plants

How long it takes your edible plant to grow should give you an indication about how much to fertilize and when to stop, says Chip Bubl, associate professor in the Department of Horticulture at Oregon State University. Radishes, for example, may produce roots ready to eat within 30 days, and you wouldn't have anything to continue fertilizing once it comes out of the ground. Alternatively, a crop like butternut squash may take several months, but you should only stop fertilizing a few weeks before you harvest. "You don’t want to douse it, but you want to give small amounts over a long time," says Bubl.

The most common issue for edible plants is that gardeners will fertilize with too much nitrogen. "With solanaceous crops [nightshade vegetables like tomatoes and eggplant], for example, you’ll get lots of leafy growth but not enough blooms, which means less of a harvest," says Irish-Hanson. "For annual vegetables, fertilize the soil just before planting. Once you see flowering and fruiting, stop with the nitrogen."

When to Stop Fertilizing Deciduous Trees and Shrubs

Most gardeners shouldn't have to fertilize a deciduous tree or shrub at all. "For homeowners, most of the trees are incorporated into a turf situation," says Irish-Hanson. Tree roots are so widely spread under the ground that they'll grab nutrients from the same fertilizer you've applied to your lawn. "The trees are going to take up the fertilizer from these areas, which means you don't have to apply it directly to the tree," she says.

With this in mind, be careful about adding nitrogen to your lawn in the fall, or stop fertilizing with nitrogen near your trees altogether. "Some woody plants take nutrients a lot in the fall, which is helpful for the plant to store for the winter," says Glen. "But if you get too much nitrogen, your plant will start growing again, and if a freeze comes, it can harm the new growth."

With fruit-bearing trees, you can fertilize until the beginning of summer, but they'll have the same issue as your other trees, where additional fertilizer past this point can cause new growth that may die off in the first hard frost.

Adding fertilizer with newly planted deciduous trees is fine, Bubl says, but the plant will be healthiest if you find the right location in your yard before you plant it. "With landscape trees, the only exception for constantly fertilizing a tree would be if you’re growing a species that doesn’t like the climate you have," says Bubl. "But this might be more trouble than it's worth."