Fertilizing Plants in Containers

Plants growing in containers usually need more regular fertilizing than plants growing in the ground. Their roots are limited to a relatively small amount of potting mix, and repeated watering can gradually leach nutrients out through the drainage holes.

The right fertilizer schedule depends on the plant, the potting mix, the type of fertilizer, how often you water, and how actively the plant is growing. The goal is to provide steady nutrition without overfeeding.

Why Do Potted Plants Need Fertilizer?

Container plants have access only to the nutrients contained within the pot. Unlike plants growing in the ground, their roots cannot expand outward into surrounding soil to find additional nutrients.

Watering also moves nutrients through the potting mix and out of the drainage holes. The more frequently a container is watered, the faster some nutrients may be lost.

University of Minnesota Extension recommends beginning regular fertilizer applications roughly 2 to 6 weeks after planting, depending on the potting mix, watering schedule, fertilizer already present in the mix, and rate of plant growth.

Slow-Release vs. Water-Soluble Fertilizer

Both types can work well in containers. The best choice depends on how much maintenance you want to do and how quickly the plant needs nutrients.

How To Apply Fertilizer To Potted Plants

Always follow the fertilizer label for application rate and frequency. Products vary widely in concentration, so one brand's directions may be very different from another's.

Water-soluble fertilizers are usually diluted in water and applied during normal watering. Illinois Extension notes that applying liquid fertilizer about every two weeks is adequate for many containers, while lower-strength fertilizer can also be used more frequently.

Slow-release products may be mixed into the potting mix at planting time or sprinkled over the surface depending on the product instructions.

How Often Should You Fertilize Container Plants?

There is no single schedule that works for every container. How often you fertilize depends on the fertilizer formulation, the plant's growth rate, the potting mix, container size, and watering frequency.

If your potting mix already contains slow-release fertilizer, you may not need to begin supplemental feeding immediately. Check the potting-mix label before adding more.

When To Fertilize Potted Plants

Fertilize container plants primarily while they are actively growing. Outdoor annuals, vegetables, perennials, shrubs, and trees generally use nutrients most actively during their normal growing season.

Plants growing slowly because of cold weather, extreme heat, drought stress, transplant stress, or dormancy generally do not need the same amount of fertilizer as plants in active growth.

Avoid relying on a strict temperature cutoff such as 50°F or 95°F for every plant. Different species respond differently to temperature. Instead, look at the plant's growth and overall condition.

If a plant is wilted from dry soil or suffering during extreme heat, correct the moisture or temperature stress first and wait until the plant has stabilized before fertilizing.

What Is The Best Fertilizer For Potted Plants?

For most mixed container gardens, an all-purpose fertilizer is a good starting point. These fertilizers generally contain nitrogen, phosphorus, potassium, and often additional plant nutrients.

The three numbers on a fertilizer package represent the percentage by weight of nitrogen, phosphate, and potash, commonly referred to as the fertilizer's N-P-K analysis.

Plants grown primarily for foliage often perform well with an all-purpose fertilizer. Flowering and fruiting containers may benefit from fertilizers formulated with proportionally less nitrogen and relatively more phosphorus or potassium.

There is no single ideal N-P-K ratio for all flowering plants, so follow the needs of the plant and the fertilizer manufacturer's recommendations rather than looking for one universal ratio.

Signs A Container Plant May Need Fertilizer

Nutrient deficiencies can cause symptoms, but many of the same symptoms can also result from watering problems, root damage, poor drainage, pests, disease, or inadequate light.

Possible signs of nutrient deficiency include:

• Pale or yellowing foliage
• Weak or unusually slow growth
• Smaller-than-normal leaves
• Reduced flowering or fruiting
• Older leaves declining prematurely

Before adding extra fertilizer, check soil moisture, drainage, light, and the plant's general health. Fertilizer will not correct a plant that is struggling because its roots are waterlogged or its container is too small.

Can You Over-Fertilize Potted Plants?

Yes. Because container roots are confined to a relatively small volume of potting mix, excess fertilizer salts can build up and damage roots.

Symptoms of excessive fertilizer may include brown leaf tips or margins, wilting despite moist soil, slowed growth, or a visible white crust of mineral salts on the soil surface or container.

The easiest way to avoid this problem is to measure fertilizer carefully and follow label directions. More fertilizer does not make plants grow faster.

Container Fertilizing Tips