When to Use 5-10-10 Fertilizer | How to Use It

If you are growing or plan to grow vining edibles such as melons, squash, zucchini, or tomatoes then it’s worth familiarising yourself with a 5-10-10 fertilizer. If it’s not already, it may soon become your biggest gardening ally. 

Out of all the different NPK formulas available, the 5-10-10 ratio that can be found in fertilizers for Pumpkins, Squash, And Watermelons is one that safely carries your vining vegetables all the way to the finish line with large, well-formed fruit.

With double the amount of phosphorus and potassium than nitrogen, this particular ratio adjusts a plant’s focus from forming healthy foliage to the formation of buds, flowers, and fruit.   

Of course, vibrant foliage will still be supported with the help of 5% nitrogen. But, any more than that the focus will remain on creating foliage. With few flowers and fruit, if any.

When growing these vegetable varieties in less-than-desirable soil, a triple 10 NPK fertilizer might be more appropriate to increase nutrient availability. Then, when buds are set on your vining veggies, a few extra organic compounds can be worked in to increase phosphorus and potassium levels.

Understanding 5-10-10 Fertilizer Labels?

5-10-10 Fertilizer

Interpreting the label of a 5-10-10 NPK and deciding if it is the best one for you, may seem daunting. Because, at the end of the day, all we gardeners really want to do is to grow healthy plants without spending a fortune. So let me break it down for you.

Most manufacturers will state the NPK ratio of their product on the label. Which will reflect how much nitrogen, phosphorus, and potassium the product contains. On the back of the container should be an ingredients list, just like you’ll find on grocery store items.

This list reveals all the ingredients that make up that product. First, the NPK content (macronutrients), then all secondary micronutrients like calcium and magnesium. Followed by trace elements such as copper and manganese. Lastly, will be any fillers the manufacturer may include, for an easy-to-use product.

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N-P-K Ratio

For those not acquainted with an NPK ratio, it is the three numbers (usually separated by dashes) that appear on fertilizer labeling. The numbers correlate with the amount of nitrogen, phosphorus, and potassium contained within the product.

A 5-10-10 NPK means 5% nitrogen, 10% phosphorus, and 10% potassium.

All plants need nitrogen, phosphorus, and potassium (also referred to as a plant’s macronutrients), but depending on the species of plant the amount required, will vary.

But what exactly do macronutrients do and why do plants need them? Well, they all work together and contribute towards the various stages of a plant’s growth cycle.

For example, they are instrumental in cell development, the process of photosynthesis, and the production of buds, flowers, and fruit.

They also help plants to absorb water effectively and can help to protect plants against extreme weather conditions (both hot and cold) and the risk of disease.

But even before all that takes place, when mixed with soil, fertilizers can help to increase soil fertility and have a positive impact on beneficial soil microbes too.


Nitrogen is vital for the growth of healthy, vibrant foliage. It does this by helping to direct energy toward chlorophyll production in plants.

t is chlorophyll that provides leaves with their green color and ensures that the process of photosynthesis can take place so that plants have enough energy to convert starches and carbohydrates into food. 

This multi-faceted macronutrient is also responsible for fueling the proteins and enzymes that ensure plants have the right amount of water and nutrients in the correct quantities in order to function effectively.

A fertilizer with a large percentage ratio of nitrogen is most often required for lawns, leafy edibles, and non-flowering plants, trees, and shrubs.


Phosphorus is the driving force behind photosynthesis because it plays a vital role once chlorophyll has been produced. Essentially, it helps to transition the stored energy in chlorophyll from starches and carbohydrates into food.

At the cellular level phosphorus also contributes to the construction of the proteins and enzymes that nitrogen then uses to regulate water and nutrients.

The other (more often talked about) function of phosphorus is how it supports the development of flowers and fruit once bud set has occurred in plants.

High phosphorus fertilizers are typically used for flowering annuals or winter greens. However, in the main specialist phosphorus fertilizers are seldom used other than in commercial applications, due to the high level of natural phosphates in garden soil.


Plants need potassium to help circulate water, nutrients, and photosynthesized food effectively.

It also activates the same

And in terms of the proteins and enzymes that phosphorus and nitrogen help to form, potassium helps to activate these proteins and enzymes so that plants form a healthy structure. 

When administered correctly and at the right time, potassium helps plants to conserve moisture and therefore protect them against diseases, extreme heat or cold, and drought by helping them to conserve moisture.

Perhaps this macronutrient’s most visible contribution to plant health and vitality is how it encourages tasty, vibrant, and plentiful crops on vining plants such as tomatoes, squash, zucchini, and melons.

Fertilizer Type

Fertilizers come in a range of options in terms of how they can be applied, how you intend to use them, and what you plan on using them for. To make it a simpler choice when deciding which one you need, here’s a look at them in more detail: 

    Fast-Acting Fertilizer

    Fast-acting fertilizers are generally used to provide an instant injection of nutrients when quick results are required.

    They are available in a few different formats. Either, as a ready-to-use liquid formula, a liquid concentrate, or a water-soluble powder. The latter two options require mixing with water before application.

    The solution is then applied directly to the soil around the base of plants and is instantly available for plant roots to absorb. Alternatively, solutions can be sprayed on foliage for absorption through leaves and stems. This is especially beneficial when leaves are yellow or brown due to nutrient deficiency.

    The pre-mixed options store well but tend to be more expensive compared to other fertilizers. Nonetheless, they are a great investment if you have just a few plants to feed and don’t have the space to store large containers or bags of fertilizer.

    One drawback with quick-release feeds is the potential to overfeed your plants. The concentrated formulas can easily lead to root burn and leaf scorching.

    Slow-Release Granules

    Available in granules or powder, slow-release fertilizers need to be worked into the soil either before planting or while plants are growing.

    Once in the soil, the formula begins working when it has been activated by water and broken down by soil microbes. Nutrients are released gradually and in a steady stream thanks to the time taken to break the granules down.

    There are many benefits to using slow-release fertilizers. You don’t have to constantly fertilize your plants for a start. Just one application can keep providing nutrients for between 4 weeks to 3 months (depending on the particular brand and what you are fertilizing).

    Another benefit is there is less risk of fertilizer burn caused by overfertilizing. This is all thanks to how the granules break down gradually and how often you need to apply them. This ensures that plants can’t absorb too many nutrients at any given time.

    In addition, the risk of leaching potentially hazardous chemicals into nearby water sources is limited when it comes to using granules. However, the risk of contaminating soil can still occur as does the distribution of chemicals when using synthetic fertilizers. 

    Granular fertilizers need to be applied around the base of trees, shrubs, and plants as evenly as possible. Getting an even coverage and avoiding contact with stems and leaves and neighboring plants that don’t need to be fertilized can be problematic when applying by hand.

    An alternative option to ensure even coverage or when fertilizing larger areas is to invest in using a broadcast spreader.

    Consideration also needs to be given to storage. Granules are usually sold in larger quantities, so unless you have a large area to cover or lots of plants to fertilize then they will need to be stored safely, kept dry, and kept out of reach of children and pets.

    Fertilizer Spikes

    Spikes offer convenience and are a mess-free solution to fertilizing. They are a compressed version of granules and are available to buy in various sizes depending on the size of the tree, plant, or shrub you need to fertilize.

    Spikes work best when you have loamy soil rather than hard clay as this makes inserting them difficult.

    Where the soil has become compacted I find that watering the area before fertilizing eases the application process. They can then be gently tapped into place using a rubber mallet.

    Just like granules, this type of fertilizer offers a gradual release of nutrients whereby the spikes are broken down over time by micro-organisms and moisture.

    There are a couple of drawbacks I find to using fertilizer spikes. Firstly, they are by far the most expensive method of fertilizing, especially if you have a large area to cover or a collection of trees or shrubs that need fertilizing.

    Another problem is the risk of causing damage to roots when the spikes are inserted into the soil. Either roots can get shredded or too much fertilizer could be absorbed by roots that are in the immediate vicinity of a spike.

    Organic Vs Non-Organic

    The ingredient list for organic fertilizers includes plant matter such as kelp and seaweed and the bi-products of animals including feather meal, bonemeal, and fish emulsion.

    Typically, these ingredients contain naturally occurring amounts of macro and micronutrients that plants need to survive and thrive.

    Inorganic fertilizers are manufactured using synthetic chemicals, fillers, and minerals. Results from using synthetic fertilizers are often impressive but there are downsides too. Some chemicals are hazardous to people and pets both if ingested and as an irritant. They also carry the risk of contaminating soil and water sources due to runoff.

    What is a 5-10-10 Fertilizer Used For?

    If you’re looking for one fertilizer to use in your garden throughout the growing season, a 5-10-10 ratio will promote healthy, robust plants. With a little extra phosphorus and potassium for flowering ornamentals, fruiting shrubs, and vegetables.

    If you grow your crops and flowers from seed, however, I do suggest starting with an NPK that’s a bit higher in nitrogen, like a 10-10-10 or even a 20-20-20 fertilizer. Plants need more nitrogen, in the beginning, stages of growth, to generate strong root systems and foliage that will carry the plant through to maturity. 

    Once buds are set, a switch to a 5-10-10 NPK will encourage more blooms and fruit, rather than just more foliage. This progression should apply to new houseplant cuttings, as well. 

    Trees and Shrubs

    Typically, non-flowering evergreen trees and shrubs rarely need fertilizing, after a few years of getting established. But, if they begin to show signs of deficiency, an NPK higher in nitrogen will help to trigger new, healthy growth. 

    For flowering varieties, like magnolia, wisteria, hydrangea, and azalea, a fertilizer higher in phosphorus and potassium (like a 5-10-10) can be introduced if a growing season goes by with few flowers. 

    Luckily, there are some low-nitrogen options that are formulated to increase or maintain soil acidity, too. This will even further benefit acid-loving plants and can be used as a fertilizer for azaleas, hydrangeas, berry shrubs, and flowering trees such as Crape Myrtle.

    Fruit Trees

    Fruiting trees and shrubs, including citrus, will need more of one macronutrient than another and at different times. A 5-10-10 works very well toward abundant flowers and fruit. While providing just enough nitrogen for lush, green foliage.

    This is especially true for smaller species when a fertilizer for fruit trees grown in pots is required. To offset the heavy leaching of water and nutrients that occurs in pots, a consistent application of a 5-10-10 NPK will maintain steady nutrient access.

    Dahlias and Other Flowers

    Flowering is an essential step in a plant’s reproductive process. The increased phosphorus in a 5-10-10 NPK stimulates healthy bud production. Followed by flowers and viable seed formation.

    Bulbs and tubers, like dahlias, experience accelerated plant maturity, resulting in buds and flowers appearing sooner, for lots of brilliant, seasonal colors. 

    The higher potassium content in a 5-10-10 NPK that is often found in fertilizers for Dahlias will not only boost drought tolerance and disease resistance in these flowering plants but also enhance crop color.

    Vegetable Gardens

    All vegetables require nitrogen, phosphorus, and potassium for root development, vigorous growth, and flowering. And some will do just fine with a balanced NPK, such as a 10-10-10. 

    But, applying a 5-10-10 NPK fertilizer, just as buds set, make tomatoes juicier and more vibrant in color. Specific fertilizers for Cucumbers and zucchini will produce tasty, plentiful crops and more seeds for the following year. And watermelon, cantaloupe, and honeydew will be ripe for creating happy memories of summer.


    Houseplants grown in fertile soil may not need as much nitrogen to maintain strong roots and healthy foliage. But, due to frequent leaching of water and nutrients, they’ll need a consistent stream of good quality houseplant fertilizer. A 5-10-10 NPK will provide what most houseplant varieties need.

    An exception would be flowering houseplants like African violets and bromeliads. Which need more phosphorus to form flowers and nitrogen for vibrant foliage. These perform far better with a 7-9-5 NPK.

    Lawn and Grass

    Phosphorus produces thick blankets of color with robust root systems in lawns and grasses. Yet, relying on nitrogen to maintain a vibrant structure that’s also resistant to wear-and-tear, excessive heat, and drought.

    Unless a soil test has revealed high nitrogen content, a 5-10-10 fertilizer may not provide enough. If it has, this low-nitrogen ratio will prevent burning and root damage. If not, a slightly higher nitrogen option may be a better choice.

    How and When to Use 5-10-10 Fertilizer

    When you’re in need of less nitrogen to prevent excessive foliage growth and need more prosperity and potassium to promote bud and flower development, a 5-10-10 fertilizer is the one to reach for. 

    The relatively low percentage NPK will provide those plants that require just a small boost of nutrients to flourish and will also reduce any risk of root and leaf burn. 

    A triple 6 fertilizer will also support color and flavor in leafy vegetables like broccoli and cabbage, grown in fertile soil. As well as kale, celery, and asparagus. Especially when these are planted in soil that just needs a small boost in nutrients. 

    Can You Use Too Much 5-10-10 Fertilizer?

    Too much phosphorus, potassium, or nitrogen can harm plants. Over-fertilization can weaken plants and leave them vulnerable to pests and diseases. Signs of overfeeding include stunted growth, browning, or yellowing of leaves and bud drop.

    When in doubt, a soil test will determine what nutrients are already present. Then, compare those results with the needs of what you’re growing. The difference will be what you need to add. 

    5-10-10 Fertilizer FAQ’s