How to Fertilize an Indoor Herb Garden

indoor herb garden

The Spruce / Cori Sears

Once you have decided on the herbs to use for an indoor garden, you will need to choose the right fertilizer. Not all fertilizers are the same and, despite some advertising claims, all fertilizers can be overused enough to damage your indoor herbs.

Types of Fertilizers You Can Use Indoors

There are many types of fertilizers that will work for an indoor herb garden. For indoor feeding, use a water-soluble fertilizer or one that can be dissolved in water. These can include: 

  • A packaged granular that you measure and dissolve in water before applying.
  • A fish emulsion that is concentrated and must be added to water before applying.
types of indoor herb garden fertilizers

The Spruce / Cori Sears

How to Apply Fertilizers

No matter which type of fertilizer you choose, you will be applying it at one-quarter of the recommended rate listed on the package. The standard fertilizer ratio is too concentrated for container plants.

In an outdoor garden, the fertilizer naturally filters out into the soil surrounding the plant and the rest of the garden. This disperses the vital components and the plant takes as much fertilizer as it needs for healthy growth. For potted indoor herbs, everything inside the container is trapped inside the pot and there is nowhere for the fertilizer to go. This can lead to a build-up and too much fertilizer can end up doing more harm than good to your plants.

To apply fertilizer in the most efficient manner, follow this procedure once a week:

  1. Mix the fertilizer at one-fourth the strength recommended by the manufacturer.
  2. Water your herb plants thoroughly. 
  3. Apply the weakened fertilizer solution. 

By watering the plant prior to fertilization, you will increase the plant's absorption rate. This is because the potting soil is already saturated and the roots are actively soaking up the water.

If you forget to fertilize for a week or more, do not over-fertilize the next time to make up for the missed opportunity. Simply fertilize as if you didn't miss a week.

applying fertilizer to indoor herbs

The Spruce / Cori Sears

Monthly Maintenance When Fertilizing an Indoor Herb Garden

It is important to do a monthly flushing out of your indoor herb plants. The containers can trap harmful elements and salts inside the soil that would normally be filtered through the soil of an outdoor garden.

Additionally, the environment inside your home is not as friendly to natural cleansing processes like fresh air circulation and rain. This can inhibit plant growth and counteract your fertilization efforts.

To keep your indoor plants healthy and happy, take the time once a month to flush the soil. It's very easy and is a chore you can do while working on other projects in your home.

  1. Simply place the herb plant in a sink and water it completely.
  2. Allow all of the excess water to drain out.
  3. Once it stops dripping, water it thoroughly once again.
  4. Allow it to drain completely in the sink and return it to its sunny spot.

This simple process will remove any salts that build up in the plant's soil and it is the perfect time for your weekly fertilizer.

watering a potted herb in the sink

The Spruce / Cori Sears

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  1. Growing Herbs Indoors. NCSU Extension.