Can You Use Indoor Plant Food Spikes on Outdoor Plants?

Plant food spikes are an easy and convenient way to feed and nourish plants. You can use fertilizer spikes on indoor and outdoor plants, but retailers often market them as different products. If you already have indoor plant food spikes, you might be wondering if you can use them on your outdoor plants.

You can use indoor plant food spikes on outdoor plants, but you may need to use more than the recommended amount. All indoor and outdoor plants need the same nutrients to survive. However, outdoor plants need higher amounts of nutrients because they grow faster.

The rest of this article will discuss using indoor plant food spikes on outdoor plants in greater detail. It will also discuss how often you should fertilize indoor and outdoor plants, the best spikes for indoor and outdoor plants, and if there are any significant differences between indoor and outdoor fertilizers.

Is It Good to Use Indoor Plant Food Spikes on Outdoor Plants?

It’s good to use indoor plant food spikes on outdoor plants, but they will not be as effective as outdoor plant-specific spikes. Since outdoor soil needs a higher level of nutrients than indoor plants during the growing season, you may need to use the indoor plant food spikes in greater numbers.

However, it’s not the best idea to use indoor plant food spikes on large plants, particularly trees. Indoor plant food spikes are small and don’t have as many nutrients as outdoor spikes. 

Thus, you would need to use a very high number of them to fertilize a tree adequately. 

If you compare indoor food spikes with outdoor tree and shrub food spikes, you can see the difference in size between them. Tree and shrub spikes are usually twice or three times the size of indoor food spikes and have higher nitrogen levels.

Differences in Nutrient Levels and Timing of Application

While all indoor and outdoor food spikes contain the same nutrients, the nutrient levels vary. Usually, there are lower amounts of nitrogen in indoor food spikes because indoor plants grow slower and don’t need as much nitrogen as outdoor plants.

All plants need nutrients like:

  • Carbon
  • Nitrogen
  • Potassium
  • Hydrogen
  • Phosphorus

However, after comparing the ingredients in the Miracle-Gro indoor plant food spikes and Miracle-Gro tree and shrub food spikes, it’s clear to see the differing levels of ingredients.

Miracle-Gro indoor plant food spikes contain:

  • 6% nitrogen
  • 12% phosphate
  • 6% soluble potash

Miracle-Gro Tree and shrub outdoor food spikes contain:

  • 15% nitrogen
  • 5% phosphate
  • 10% soluble potash

As you can see, outdoor spikes contain a much higher concentration of nitrogen and soluble potash. However, they have less phosphate, and since nitrogen is the essential nutrient for outdoor plants, you’ll need to ensure you’re using enough indoor spikes on your outdoor plants.

Why You Might Need Both

The primary difference between indoor and outdoor plant food is in the timing of the application. Typically, indoor plants grow more slowly than outdoor plants because they receive less sunlight than outdoor plants, which means they don’t need to be fed as much nitrogen as outdoor plants. 

Outdoor plants use nitrogen fairly quickly in the growing season and need frequent applications. However, you can’t add too much inorganic fertilizer at once because the concentration of salts will cause the fertilizer to burn your plants. 

Plants rooted in garden soil outside have a better chance of surviving fertilizer burns because the compacted nature and high water retention prevent quick fertilizer dispersal.

The time taken by fertilizer to disperse through the soil is also an important determinant of how much and how often fertilizer needs to be applied. This is determined by the compaction of the soil and the frequency of irrigation. 

Indoor plants can be fertilized throughout the year because the soil doesn’t harden in the winter, though this is inadvisable if your plant is not an evergreen. They are also watered less than outdoor plants, so they need very low quantities of fertilizer, applied less frequently. 

Outdoor plants need a lot of fertilizer in the growing season. 

Depending on the type of fertilizer, applying more frequently may not be necessary. Liquid fertilizer disperses faster through the soil, making nutrients readily available to your plants. 

However, liquid fertilizers are more prone to nutrient loss through volatilization, especially with foliar applications, and will need to be reapplied more frequently. Too frequently, and the fertilizer could cause leaf or root scorch, so you will need to dilute the fertilizer heavily.

When using liquid fertilizers as a starter solution for new seedlings that have been recently transplanted into the soil, you’ll want to use an extremely dilute application at the time of planting. 

You should also wait a few weeks for the plants to root before applying any more.

The starting solution can also be used for newly transplanted indoor plants in the same way, but you can wait much longer before needing to apply fertilizer again.

How to Use Indoor Plant Food Spikes Outdoors

Installing indoor plant food spikes outdoors works similarly to how you would plant outdoor food spikes. However, since indoor plant food spikes generally carry lower levels of essential nutrients, you’ll need to install them more frequently.

Here’s how to use indoor plant food spikes outdoors:

  1. Determine how many spikes you need. Most packages tell you how many spikes you need depending on the pot’s diameter or plant. Since indoor food spikes cover less surface area than outdoor spikes, you may need to use a lot of them.
  2. Place the spike(s) in the soil. You’ll need to make a hole in the soil to place the spike securely inside.
  3. Cover the spike with soil. Cover it completely with more soil once you’ve fully submerged the plant food spike into the ground.
  4. Replace spikes every 1-2 weeks during summer. Most indoor plant food spikes need to be replaced every 30 days during summer, as you can see on its instruction pack. So you’ll need to replace them more frequently than this if using them outdoors. 

It’s important to note that most indoor plant food spikes cover less surface area than outdoor plant food spikes. For example, two Miracle-Gro indoor plant food spikes cover 3-4 inches (7.62-10.16 cm) of area. On the other hand, one Miracle-Gro tree and shrub spike cover 4 feet (1.2 m).

What Is the Right Timing and Frequency?

You should use fertilizer spikes on outdoor plants twice a year in most cases, once during spring and once during fall. In some instances, you may want to fertilize your plants more frequently during summer because plants need the most nutrients.

Generally speaking, outdoor plants don’t need to be fertilized as frequently as houseplants during the growing periods. This reduced requirement is mainly because outdoor plants have more natural nutrients, as mentioned earlier.

However, since houseplants tend to grow slower than many outdoor plants, they often don’t need a lot of fertilizer. Therefore, it’s possible to overfertilize indoor plants.

If you fertilize your outdoor plants too frequently, you’ll risk giving them too many nutrients at once, and it could result in fertilizer burn. Eventually, this can kill outdoor plants, so you must be cautious.

Factors to Consider When Selecting Fertilizer for Garden Plants

When determining a good fertilizer for your outdoor plants, you need to consider the following factors:

Nutrient Requirements

The nutrient requirements of your plants will vary. 

Grass and trees typically need fertilizers with a higher nitrogen ratio. On the other hand, tomato plants need larger phosphorus ratios to help them flower and potassium to help with water intake during the fruiting season.

Identifying your plant’s nutrient requirements and how much they need at a time is essential to identifying the best fertilizer.

All plants require the same 18 nutrients, but the quantities they need vary from plant to plant. 

For the most part, plants need three macronutrients and multiple micronutrients to help them develop strong roots and grow well. The presence of nutrients also determines the quality and quantity of the yield. 

Plants need the same macro and micronutrients, whether they’re indoors or outdoors. However, indoor plants need micronutrients added to the fertilizers more often than outdoor plants. Most garden soils have adequate micronutrients as long as the pH value is maintained between 6-7. 

Outdoor plants receive a great deal more sunlight and moisture than indoor plants, and if they’re well-fed, they grow healthier and bigger than indoor plants do. To grow as big as they can and need to, these plants need large amounts of macronutrients, particularly nitrogen. 

When planted directly into garden soil, plants must compete for essential nutrients. Plants and lawns typically use more nitrogen than the soil can supply, so amending the soil with nitrogen-heavy fertilizers is especially important for outdoor plants. 

The other common nutrient deficiency among outdoor plants is phosphorus. Phosphorus is crucial for root growth and development, which is one of the most important goals of nutrient application. Proper root growth ensures that the plants reach as far as they need to and absorb all the nutrients in the soil. 

Since nitrogen and phosphorus are important for plant growth, they’re among the first nutrients outdoor plants use. However, the application of fertilizers with these nutrients needs to be timed to ensure that the plants receive the nutrients when they need them most, which is during the growing season. 

The Immediacy of Requirement

The immediacy of nutrient requirements varies depending on the time of year and their growth stage. Mature outdoor plants in dormancy will benefit from the application of organic fertilizer that will release nutrients slowly and enrich the soil overall.

On the other hand, young plants and plants in the growing season have more immediate nutrient requirements that are best met by inorganic fertilizer. Remember, these fertilizers should be applied carefully to prevent scorching. 

Size of the Plant

The size of the plant determines how much nutrient it needs and how often it needs it.

Trees can be fed with a few plant food spikes for the entire growing season, though too many spikes too close to a tree can kill it. Meanwhile, lawns and vegetables need more frequent fertilizer applications to compensate for their root systems, lack of nutrient storage, and high yields required. 

Soil Fertility

A complete soil analysis is always a good idea to help you determine the right kind of fertilizer for your outdoor plants. It will let you know what nutrients are missing and need to be fed into your soil to ensure that your outdoor plants are receiving the nutrients they need. 

Soil Compaction and Water Retention

Soil compaction refers to the texture of your soil and how tightly the particles stick to each other. Liquid fertilizers are better for compact soil, as they will disperse faster to the roots and are easily absorbed by plants.

Slow-release fertilizers like compost or plant food spikes, including the spikes used for indoor plants into the soil, are good options throughout the year. These will help supply nutrients in necessary quantities while improving overall soil health. 

Contrasting Feeding Requirements

It’s essential to understand the differences between feeding indoor and outdoor plants. While many assume they both work the same, this isn’t necessarily the case. Indoor plants don’t have access to fresh outdoor air and fresh, earthy soil. 

They also don’t experience as much moisture due to the lack of rain indoors.

Here are some things to consider when it comes to fertilizing indoor and outdoor plants:

Consider the Soil Requirements

You must consider the soil requirements. The soil outdoors is much more challenging to control than the soil indoors. And as I’ve mentioned already, the soil outdoors is likely to have higher levels of nutrients occurring naturally.

The best thing to do is get a soil test for your outdoor soil. That way, you can see what nutrients you need to provide your plant. From there, you can decide whether or not it’s appropriate to use indoor plant food spikes on outdoor plants.

Characteristics of Garden Soil

Most garden soil is made up of sand, silt, and clay particles. The amount of each of these particles determines the texture of the soil. Sandy soils have very high drainage, while clay soils are very compact and hold on to water. 

The more compact a soil, the harder it is for roots to draw nutrients from it as the particles stick to each other and the roots. It’s important that garden soil be amended with organic fertilizers like manure and compost to improve drainage and the overall nutrient composition of the soil.

Garden soil also tends to get colder and freeze in the winter, which compacts it all the more. 

Plants kept indoors in a temperature-controlled environment may continue growing through the winter, especially if they are tropical plants. But plants outside will enter dormancy, and any inorganic fertilizers added at this time will not be used. 

Amending garden soil with organic matter also helps introduce more organisms into the soil. 

These organisms include microbes and earthworms, as they help aerate the soil and improve soil health and texture. Slow-release fertilizers, especially the ones activated by microbial activity, are also a good way of improving soil health gradually.

You can incorporate plant materials like leaves, straw, and grass directly into your soil if you’re planting outdoors in your garden and have planned it well in advance. Adding plant materials to your soil in the fall will ensure a richer soil by spring. 

Even after adding organic matter, plants rooted outdoors in garden soil need a great deal of additional fertilizer, especially in the growing season. Of course, all plants need to be fed in the growing season, but outdoor plants need additional help as garden soils are easily depleted of macronutrients. 

Differentiation of Nutritional Needs

You must remember that indoor and outdoor plants often need different amounts of nutrients, so it’s not always the best idea to have your indoor and outdoor plants on the same feeding schedule. 

The differences in requirements don’t mean that you can’t use the same fertilizer for indoor and outdoor plants, but it does mean that you should pay attention to when you should fertilize them separately, and how many spikes you use each time.

Can You Use Any Fertilizer on Outdoor Plants?

You can’t use any fertilizer on outdoor plants. For example, lawn fertilizer can contain harsh chemicals like herbicides, and they can damage plants. Plus, some fertilizers may have too much, or not enough, of certain nutrients that your soil needs.

So, you shouldn’t just pick up any fertilizer and use it on your soil. It’s important to know what your soil needs first, and then you can decide on the most appropriate fertilizer.

In many cases, indoor fertilizer spikes are fine for outdoor plants. But if your soil needs an exceptionally high amount of phosphorus or nitrogen, you’ll need to make sure you choose a fertilizer with higher amounts, which you won’t find with indoor food spikes.

On the other hand, your soil may only need a small amount of a particular nutrient, which you would find out through a soil test. Some indoor fertilizer spikes may contain too much of it, which is another reason why you’d need to use a different fertilizer.


You may use indoor food spikes on outdoor plants because they contain the same macronutrients. However, outdoor plants need to be fed more frequently than indoor plants because they grow quickly during the summer and need more nitrogen and potassium. 

Indoor food spikes generally contain less nitrogen than outdoor food spikes, which is another essential point to remember. So, if your soil is deficient in nitrogen, it’s best to stick with a fertilizer with higher nitrogen levels rather than indoor food spikes.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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