Top 6 Slow-Release Fertilizers for Houseplants & Veggies

slow release fertilizer

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Slow-release fertilizers are great for houseplants and vegetable garden due to their ability to gradually release nutrients over an extended period, reducing the frequency of applications and potential nutrient losses.

In this review article, we will review 6 popular brands to help you make informed decisions when selecting the best one for your plants.

Quick Summary

Product

Review

Editor's Pick

Burpee

4-4-4 NPK

Pros:

- 100% natural and organic
- contains micronutrients and microbes
- suitable for all plant types
- feeds up to 3 months
- cheap

Cons:

- none

Osmocote Plus

15-9-12 NPK ratio

Pros:

- high potassium number good for fruits
- contains micronutrients
- feeds up to 6 months
- economical

Cons:

- not organic

Osmocote Smart-Release

14-14-14 NPK ratio

Pros:

- suitable for all types of plants
- feeds up to 4 months

Cons:

- no micronutrients

Espoma plant tone

3-3-3 NPK ratio

Pros

- 100% natural and organic
- contains beneficial microbes
- contains Calcium and Magnesium

Cons

- low potassium number
- expensive
- feeds up to a month

Tezula Nutricote

18-6-8 NPK ratio

Pros

- conatins micronutrients
- feeds over 6 months

Cons

- low phosphorus and potassium
- expensive

Miracle Gro

12-4-8 NPK ratio

Pros

- high nitrogen good for foliage plants

Cons

- expensive
- not organic
- not ideal for fruits and flowers

How to choose a good slow-release fertilizer?

When selecting a slow-release fertilizer for plants, there are several factors to consider:

Nutrient content:  Slow-release fertilizers come in different formulations, with varying amounts of macronutrients like nitrogen (N), phosphorus (P), and potassium (K). Plants with only foliage require more of nitrogen, while flowers and fruits need more potassium and phosphorous. 

Choose a fertilizer with the appropriate balance of nutrients for the specific plants you want to feed.

Release rate:  Slow-release fertilizers release nutrients over an extended period, ranging from several weeks to several months. Sulfur coating release nutrients at a slower rate than polymer coating and thus can last longer in soil. 

Soil type: Soil type affects the availability of nutrients to plants.  For example, slow-release fertilizers with sulfur coatings are better suited for acidic soils. Choose a fertilizer that is compatible with your soil type.

Environmental factors: Environmental conditions such as temperature and moisture affect the rate at which fertilizers release nutrients. Consider the local climate and weather patterns when selecting a slow-release fertilizer.

Application method: Slow-release fertilizers come in different forms, such as granules, pellets, or spikes. Choose a fertilizer that is easy to apply and distribute evenly around your plants.

Cost: Slow-release fertilizers can be more expensive than other types of fertilizers. Consider the cost per application and the long-term benefits of slow-release fertilizers when making your selection.

Overall, it is important to choose a slow-release fertilizer that meets the specific needs of your plants and is compatible with your soil type and environmental conditions.

Slow-release fertilizer reviews

1. Burpee – Editor’s Pick

Burpee’s slow-release fertilizer is our favorite and also has received the highest number of reviews. 

It is 100% natural and organic.  It contains only bone meal which provides phosphorus and calcium and blood meal which provides nitrogen to the plants.

With a 4-4-4 NPK ratio, it is an all-purpose fertilizer for all types of plants.  It also contains micronutrients and beneficial microbes to improve soil fertility naturally.

Each application can feed up to 3 months.

It has been tested with growing tomatoes and seedlings with many great results.

The bonus is that it is also the most economic on our list.

Our score: 5 out of 5

2. Osmocote Plus

Osmocote Plus has a 15/9/12 NPK ratio with micronutrients: Magnesium, Sulfur, Boron, Copper, Iron, Manganese, Molybdenum, and Zinc. 

It works for all plant varieties including acid-loving plants because it contains both ammoniacal nitrogen and nitrate nitrogen.

Each granule is coated with resin which allows nutrients to release slowly to feed up to 6 months and does not contaminate the soil.

The high proportion of potassium is ideal for flowers, tomatoes and other fruits.

It is available in 1lb, 2lb, and 8lb packages and is very economical because 1 scoopful can be used for a 2-gallon pot or an area of 4 square feet (or an area of 0.6 x 0.6 meters). 

It is the most popular product and receives high ratings.

The only downside is that it is expensive, more than double than Burpee.  Also, it is not organic and may not be preferred for growing vegetables and fruits.

Our score: 4 out of 5

3. Osmocote Smart-Release

The highlight of this product is that it can be used with fruits and vegetables for 4 months.

It has a 14/14/14 formula with equal parts of nitrogen, phosphate and potassium/potash.  However, it does not contain micronutrients.

It is suitable for a variety of crops including acid-loving plants because it contains both ammoniacal nitrogen and nitrate nitrogen.

Each granule is coated with resin which slowly releases nutrients.

Our score: 4 out of 5

4. Espoma plant tone

This is our favorite product because it is 100% natural, derived from feather meal, poultry manure, bone meal, alfalfa meal, greensand, sulfate of potash, and sulfate of potash magnesia.

It also contains beneficial microbes.

It has a 5-3-3 NPK formula with Calcium and Magnesium.

It can be used with acid-loving plants.

However, its low phosphorous and potassium number makes it not very ideal for flowers and fruits. 

Also, this product is that it is expensive, more than double than Burpee which is also organic.

Also, each application can only feed up to a month, not as much as other brands.

Our score: 4 out or 5

5. Tezula Nutricote

This time-release fertilizer by Tezula differs from other leading brands with the polymer coating which is not temperature sensitive, meaning that it can dissolve and release nutrients during cold days.

It contains micronutrients: Magnesium, Boron, Copper, Iron, Manganese, Molybdenum and Chlorine. 

Each application feeds over 6 months.

It can be applied to all plants both indoors and outdoors, including all kinds of orchids and bonsai with great results.

The bonus with this product is that the product comes with a ziplock package so that the pellets can last over 3 years if stored properly.

However, this is an expensive product.

Also, with a 18-6-8 NPK ratio, this fertilizer may be more suitable for houseplants with mostly foliage, but not for flowers, tomatoes and fruits because of a low potassium number.

Our score: 4 out of 5

6. Miracle-Gro

This is a slow-release fertilizer with a 12-4-8 NPK ratio and micronutrients.

The bottle has a convenient “shake-out” design that you can just shake the pellets out of the bottle where you want to fertilize.

This product works well with houseplants with mainly foliage, but may not be ideal for flowers, tomatoes, and fruits because of the low phosphorous content.

Some gardeners have reported signs of nutrient deficiencies after applying the product, e.g. leaves showing yellow mosaic patterns which are signs of nitrogen deficiency, purple stems, pale leaves, bud drop, stunted fruits, and slow ripening.

Also, it is an expensive product.

Our score: 3.5 out of 5

How to apply slow-release fertilizer?

Applying slow-release fertilizers correctly is essential to ensure that the plants receive the necessary nutrients without any adverse effects.

Here are the steps to apply slow-release fertilizer effectively:

  1. Determine the type of slow-release fertilizer you have and read the instructions carefully. Different slow-release fertilizers have different application rates and methods.
  2. Check the soil’s moisture content before applying the fertilizer. If the soil is dry, water the plants thoroughly before applying the fertilizer.
  3. Spread the slow-release fertilizer evenly over the soil surface, following the recommended application rate. If you are applying the fertilizer to potted plants, mix the fertilizer into the potting soil.
  4. Lightly rake the soil surface to incorporate the slow-release fertilizer into the soil.
  5. Water the plants thoroughly after applying the slow-release fertilizer to help activate the nutrients and ensure they reach the plant roots.
  6. Avoid applying slow-release fertilizer during periods of heavy rainfall or when the soil is waterlogged, as this can cause the fertilizer to leach out of the soil and potentially harm nearby waterways.
  7. Monitor the plants’ growth and adjust the fertilizer application rate as needed. Remember, slow-release fertilizers release nutrients over an extended period, so it may take several weeks to see the results of the application.

By following these steps, you can apply slow-release fertilizer effectively, providing your plants with the nutrients they need to thrive.

Happy gardening!

Related

Slow-Release vs Fast-Release Fertilizer: Which is Better?


Carol loves to garden and research to help others grow their green thumb.

She is working towards her dream of living close to nature.

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