Fertilizing Containers: Tips for Feeding Plants in Pots (2024)

For flower and vegetable containers that look great all summer long, a continuous supply of nutrientsis an absolute must. Here are tips for feeding plants in pots, including a simple 3-step process that ensures your potted pals are getting what theyneed.

The Importance of Nutrients for ContainerPlants

My containers filled with petunias, salvia, lettuces, and tomatoes looked awful, especially compared to those I planted in the ground later. I was accidentally starving the container plants because I didn’t replace nutrients leached out of the potting mix every time I watered. Unlike plants in the ground, which haveroots to seek out additional nutrients, container plants are effectively quarantined from the nutrients, fungi, and bacteria naturally found in soil.

If you grow plants in containers, you must also lend a helping hand. Even using high-quality potting soil or compost, plants exhaust the available nutrients in containers within six weeks.

Sure, you can sprinkle some fertilizer pellets, as you might do with vegetables grown in the ground. But even that won’t be enough for some container plants, especially tomatoes and other big feeders! Aregular liquid feed is best.You can buy liquid fertilizers or make your own. Diluted with water, they provide a shot of extra nutrients that ensure plants continue to grow well and beproductive.

My 3-Step Container FertilizerProgram

Now, I use this three-step fertilizer program, and my container gardens flourish. Be sure tofertilize…

1. …when you are filling your containers with pottingmix.

When starting your containers, incorporate fertilizer pellets into your potting mix.(If the potting mix contains fertilizer, skip this step.) You want “slow-release” fertilizer pellets coated with a polymer that lets them dissolve at varied rates; the thicker the coating, the longer it takes for the fertilizer in pellets to be released into the potting mix. Most brands feed plants for at least 60 days, but some supply a steady stream of nutrients for up to 120 days. Check the label on any product you buy for thisinformation.

Slow-release food is also available in organic form. Fish meal pellets are formulated similarly to synthetic fertilizers. Cotton seed meal, feather meal, and alfalfa pellets are other slow-release, organic choices. All feed plants for about 60 days. The alfalfa also contains a hormone, triacontanol, which promotes plantgrowth.

2. …as your plantsgrow.

Apply a water-soluble (liquid) fertilizer to supplement the slow-release fertilizer. Water-soluble ones deliver nutrients directly to plant roots and are easy to apply. Dissolve them in water and pour the liquid into the container for a nutritional boost. Follow package directions for dilution rates and the amount of fertilizer to use on eachcontainer.

If you are buying liquid fertilizer, many types are on the market. You want an equal ratioof “N-P-K” (nitrogen, phosphorus, potassium), which are the three nutrients that all plants need. A fertilizer with an equal amount of each nutrient is commonly called a “balanced” fertilizer, which you’ll see reflected in the label (e.g., 10-10-10). However, fruiting crops such as tomatoes and peppers need a liquid fertilizer with more phosphorus (P). For leafy plants such as lettuce and spinach, it’s fine to have more nitrogen to produce foliage, but any other plant would produce leaves at the expense offruit.

Organic choices such as fish meal emulsion and liquid kelp also work very well. In fact, some plants, like ferns and lettuce, respond better to organic products than syntheticfertilizers.

I like to usea liquid feed made from seaweed. I water all my vegetables with a dilute seaweed feed about once a month.Fruiting vegetables will need a tomato feed weekly (alternating with the seaweed feed once a month). Fertilize throughout the growing season from spring until latesummer.

Note: Some container plants really do not need to be fed as they grow. Cut-and-come-again lettuces or other salad leaves don’t typically need a regular feed, as they are usually harvested before they use up their supply. Herbs, particularly lavender, thyme, or rosemary, shouldn’t need to be fed at all; they do best in nutrient-poor, drierconditions.

3. …if plants appear stressed or need apick-me-up.

If plants need a quick pick-me-up due to stressors (such as extreme temperatures or drought) or heavy production of flowers or fruit, apply fertilizer directly to plants’ leaves. Deadhead old blooms, cut back damaged foliage, and then spray water-soluble fertilizer on leaf tops and undersides. The foliar spray delivers nutrients directly to where photosynthesis takes place. Results are dramatic—you’ll see growth or renewal almostovernight.

If plants are looking a bit under the weather, I water with my diluted seaweed solution or even spray theseaweed solution directly onto the leaves and that will often sort themout.

Use any spray bottle or garden sprayer and follow the dilution rates given on the fertilizerpackage.

A word of caution about foliar feeding: Don’t do it when temperatures are above 90ºF or when the sun is beating on plants directly. The fertilizer could burn leaves. The best time to foliar feed is in the morning or earlyevening.

Make Your Own LiquidFertilizer

Liquid fertilizer can get pricy, depending on the size of your container garden, so consider making your own by steeping “weeds” or other nutrient-packed plants inwater.

Comfrey is commonly used in homemade liquid fertilizer. It’s great for fruiting vegetables because it contains a good dose of potassium. Nettles or borage can be used in the same way for a higher-nitrogen alternative, which is beneficial for leafyvegetables.

→See our post on how to make organic fertilizer from comfrey or other herbs andweeds.

CompostTea

You could also make a “Compost Tea,” which is a good overall plant health booster (a little like vitamins for people) and helps plants be better able to resist pests anddiseases.See howto make compost tea.