In a natural environment, the plants growing within the water receive nutrients from the natural decomposition of plant and animal life around them. In a typical water garden, marginal and deep-water submersible plants may require supplements of fertilizer or food until their ecosystem becomes balanced. Fertilizing aquatic plants requires precision both in choice of the fertilizer and its application. You’ll want to avoid adding too many nutrient chemicals to the water itself, which may cause harm to plants that need few added nutrients, as well as to fish and other wildlife. Fertilizers may promote algae blooms and overstimulate plants that are best fed by natural processes.

Yellowing aquatic plants
Many aquatic plants spread new foliage from the moment that they are given a home in your water feature. They receive most of their nutrients from the water itself, recycling decayed plant matter and helping to clean the water of excess nutrients. When their growth slows or leaves turn yellow, it may be time to fertilize.
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard
Aquatic fertilizer spikes
Slow-release aquatic plants fertilizer spikes are formulated with slow-dissolving synthetic chemical fertilizers appropriate for aquatic plants in home water gardens.
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard

There are four times to consider fertilizing your aquatic plants:

  1. At planting.
  2. In the early part of the growing season to help aquatic plants emerge from dormancy.
  3. When plants are repotted after division or thinning.
  4. When a specific plant shows signs of distress.

Each aquatic plant species has specific nutrient needs. Follow the plant label or ask the aquatic specialist at your local garden center or water garden nursery for help with the specific plants you’ve purchased. Whatever you do, avoid using the same nutrients and application methods recommended for your inground plants – their needs are much different than the plants growing in your garden pond.

When fertilizing plants in your water garden, use slow-release fertilizer tablets designed especially for aquatics. These tablets contain appropriate levels of nitrogen, potassium, phosphorous and other nutrients that water plants require. Check the package’s instructions for the amount to apply for your specific plant’s needs. Embed the fertilizer tablets in the soil under the topdressing of gravel, where they’ll dissolve slowly over time and remain, for the most part, within each plant’s container. In addition, some nutrients can be spray-applied to the exposed leaves for immediate absorption, also in proper dilution and dosage per label instructions.

You’ll know if an individual plant is in need of fertilizer: It will become stunted, stop growing, or display discolored or limp foliage. Remove the troubled plant and its container from the water feature and care for the plant individually. Inspect for signs of pests and diseases before fertilizing and returning the plant to the water.

As you fertilize or otherwise treat your surrounding landscape – whether shoreline plants, the lawn or flower/vegetable garden – take care to avoid contaminating your water feature with garden chemicals. They may alter or damage the delicate balance of the water and plants in your feature’s ecosystem or cause algae to bloom!

While most submerged aquatic plants get the bulk of their nutrients from the water, marginals occasionally require extra boosts from fertilizer because most of their growth occurs above the water surface. Condition the soil of young, overwintered, divided or repotted plants with encapsulated slow-release granules. Fertilize the plants every 2 months during the growing season. Wear a pair of long rubber gloves, poke fertilizer pellets into the damp soil and take the steps in the following pictures and captions for two fertilizing options.

Slow Release Aquatic Fertilizer

Slow Release Aquatic Fertilizer - Step 1

Slow Release Aquatic Fertilizer - Step 1

Slow-release Fertilizer Application, Step 1: Remove the plant from the water feature and allow it to drain. Use care to protect foliage from harm, especially when handling large plants.
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard
Slow Release Aquatic Fertilizer - Step 2

Slow Release Aquatic Fertilizer - Step 2

Apply slow-release tablets for aquatic plants (and for the specific species). Insert tablet into the soil below the gravel topdressing, as directed on the fertilizer package.
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard
Slow Release Aquatic Fertilizer - Step 3

Slow Release Aquatic Fertilizer - Step 3

Replace the fertilized plant in the water feature. Fan its foliage, eliminating tangles or inverted leaves.
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard

Liquid Foliar Aquatic Fertilizer

Liquid Foliar Aquatic Fertilizer

Liquid Foliar Aquatic Fertilizer

Remove the plant to be fertilized from the water feature. Carefully following all package instructions, spray-apply liquid foliar fertilizer on floating and standing foliage. (Do this monthly during the growing season.) Allow the foliage to dry completely before returning the plant to the water. (Foliar fertilizers are absorbed directly through the foliage rather than through the roots.)
Photo Credit: ©2001 Dolezal Publishing/John M. Rickard