9 Best Fertilizer For Zucchini | How And When To Use

Fertilizer is crucial for most plants to succeed, and this applies to zucchini too. Luckily, they’re not too hungry plants and you won’t have to fertilize them on a frequent basis. This doesn’t mean that you can just choose any fertilizer and apply it randomly.

To avoid such problems, I’ll be sharing all I know about the best methods of fertilization, as well as the best fertilizer for zucchini in this article.

Choosing Zucchini Fertilizer

Zucchini needs plenty of nitrogen, phosphorus, and potassium, but it doesn’t need so much in the way of other micronutrients such as iron and magnesium as other plants do. Although, there may be occasions when your zucchini plants may be suffering from a calcium deficiency, however, more about that below.

Because of this, when you’re choosing your fertilizer, know that the NPK ratio is more important than anything else.

The only instance when a micronutrient is important for zucchini is the lack of calcium in the soil, but we’ll get to that later.

Top Zucchini Fertilizers

If you’re in a hurry to choose, then check out my top recommendations here. Alternatively, to understand all the facts and know-how about how to correctly fertilize zucchini, including why, how, and when is best to fertilize, then be sure to read to the end.

Best Slow-Release Granules

Burpee Natural Granular Organic Food 4-4-4

Slow-release granules containing an even balance of NPK – just how zucchini plants prefer.

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Best Organic Fertilizer

Dr. Earth Organic All Purpose Fertilizer 4-4-4

A perfectly balanced organic fertilizer. Gentle enough even for new plants and suitable for use throughout the growing season.

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Best Fertilizer for Potted Zucchini Plants

Neptune’s Harvest Veg Fish Fertilizer 2-4-2

An organic, liquid concentrate fertilizer that will provide zucchini plants with an instant boost as well as improve the soil when prone to nutrient deficiencies.

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N-P-K Ratio

NPK is the ratio of nitrogen, phosphorus, and potassium in the fertilizer. These are the three most important nutrients to plants, and every fertilizer has a declaration of the NPK ratio on the packaging.

Because zucchini needs large amounts of all three, it’s best to apply a fertilizer that’s high and balanced. A 10-10-10 ratio does very well with zucchini, but a 5-5-5 can do fine too, as long as you apply it in appropriate amounts.

The numbers indicate the percentage of the nutrient in the fertilizer mix. If the declaration says 5-5-5, then there’s 5% of each nutrient in the mix.

Fertilizers will greatly affect the soil of the plant, so it’s important to keep soil pH and fertilizer micronutrients in mind when choosing the fertilizer.

Soil pH and Nutrient Uptake

Zucchini doesn’t have any special pH requirements – provided it’s in the range of 5.5 to 7.5 – it can stand both slightly acidic and slightly alkaline soil.

When it comes to micronutrients (non-NPK nutrients), zucchini is a hardy plant that doesn’t need much care in that department.

Calcium Deficiencies

Fertilizers rich in calcium are usually sought after because of something called ‘blossom-end rot, which occurs when there’s a deficiency of calcium in the plant. This usually happens because the plant can’t absorb calcium from the soil.

There are two reasons why a plant can’t absorb calcium – there might not be enough calcium in the soil or there could be too much salt. Using fertilizer rich in calcium will most definitely enrich the soil and prevent blossom-end rot.

However, if the soil has too much salt, then this type of rot can’t be solved with fertilizer rich in calcium. ‘Soil salinization’ is solved through chemical treatment and soil flushing.

Granular vs Liquid Fertilizer

There are two major differences between granular and liquid fertilizers.

The first one is the method of application. Liquid fertilizers lead the way in this regard, as all you have to do is mix them with water (following the manufacturer’s instructions) and pour them into the soil. Some brands even produce ready-to-use formulas which make the whole application process even easier.

Granular fertilizers, on the other hand, require digging the soil, spreading the granules, and watering them plentifully.

The second difference is the rate of nutrient release. Granular fertilizers have the upper hand in this aspect, as they slowly release nutrients when applied. This means that you won’t have to fertilize as often.

Liquid fertilizers are quick-release fertilizers, and the plant drinks up the nutrients very quickly. 

Both methods can lead to falling foul of overfertilization. This is where the product is applied in too greater quantities or too often.

Synthetic vs Organic Fertilizers

Organic fertilizers are derived from animal and plant matter that contain naturally occurring macro and micronutrients. Whereas, the ingredient list for synthetic fertilizers contains compounds that have been manufactured to replicate the macronutrients nitrogen, phosphorous, and potassium. 

Whilst some of the ingredients in synthetic fertilizers are derived from organic fertilizers, they will have been processed in some way. As a result, they are usually easier to use and break apart to release nutrients.

There always have been and there always will be arguments for and against the use of synthetic fertilizers. However, synthetic fertilizers are not dangerous for your plants if you know what you’re doing. 

Sure, if you use too much of them, you could kill your plants and potentially contaminate local water sources. But if you’re careful, you’ll be delivering strong, potent fertilizers to your plants. 

In addition, when using synthetic fertilizers on fruit and vegetables that you are going to eat, you’re going to want to wash them thoroughly once you’ve picked them and before you handle, prepare and eat them.

Organic fertilizers 

To become effective, organic fertilizers need to be broken down by beneficial bacteria found in soil and this process can take a while. 

The potency of organic fertilizers tends to be weaker compared to synthetics, and in combination with their natural slow rate of nutrient release, this makes organic fertilizers more difficult to overfertilize your plants with.

They carry less risk of causing harm to the environment, local water sources, people, and pets. However, they are not completely hazard-free. You’ll still need to read the label and were protective clothing when applying organic fertilizers.

Fertilizers for Zucchini Reviewed

Here’s a pick of the nine best zucchini fertilizers on the market.

1. Burpee Natural Purpose Granular Organic Food 4-4-4

Best Slow-Release Granules

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Pros: 

• Even NPK that’s beneficial to zucchini plants
• Can be used for many other edibles
• Slow-release formula with faster-than-expected results

Cons: 

• May need additional applications due to the gentle NPK ratio

If slow-release granules are what you are looking for when it comes to feeding your zucchini, then this option from Burpee may be exactly what you are looking for. 

An even balance of macronutrients that’s ideal for zucchini plants, certified organic – making it ideal for feeding, and once applied, there’s no need to feed again for another 3 months.

Organic certifications from OMRI guarantee that this granular fertilizer is completely organic, while micronutrients include calcium and beneficial microbes. 

Although it’s granular, the manufacturer’s claim that this fertilizer is actually more fast-acting than other similar products means that results can be seen in a very short time. I can vouch for that too! I tried it on a ground-planted zucchini right from the time of planting and the yield was plentiful and disease free.

How to use: When applied according to the manufacturer’s instructions, it can feed your plants for three months before needing reapplication. It’s a great fit for plants in pots, as well as plants in open soil.

2. Dr. Earth Organic All Purpose Fertilizer 4-4-4

Best Organic Fertilizer

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Pros: 

• Well-balanced NPK that zucchini prefer
• Difficult to overfertilize
• Utilizes beneficial soil microbes for overall soil and plant health

Cons: 

• ‘Organic’ odor that some find very strong

This is a well-balanced organic fertilizer, and while it packs a bit of a weaker punch when compared to 10-10-10 fertilizers, you’re definitely safe from overfertilization. 

This is a slow-release formula that uses absolutely no artificial ingredients and carries the highly regarded OMRI certificate so you can be sure your providing your zucchini plants and other garden edibles with a top-quality fertilizer.

In addition, the beneficial soil microbes improve soil quality and make it easier for your plants to absorb nutrients. Nutrients are derived from land and ocean plants, fish and fish bones, as well as minerals from the ground.

How To Use: For container zucchini plants: Mix 2 heaped tbsp with 1 gallon of potting soil. Dig in and water the well. Repeat monthly. For ground-planted zucchini, mix 1&1/3 cups into 10sq ft of soil. Dig in and water the well. Repeat every 2 months.

3. Neptune’s Harvest Veg Fish Fertilizer 2-4-2

Best Fertilizer for Potted Plants

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Pros: 

• A fast-acting liquid that can be used as a fertilizer and foliar spray
• Improves drought and high-temperature resistance
• Suitable for use with other vegetables too

Cons: 

• Strong odor 

This fertilizer is a bit unique in comparison to other fertilizers on the list because it helps with drought tolerance so it’s especially good for container-based plants that tend to dry up quicker than those planted in the ground, or when growing in drier regions. 

This fast-acting liquid fertilizer helps to improve root health and foliage growth, making the plant more resistant to high temperatures and that’s all thanks to the nutrients that are derived from seaweed, fish, and molasses.

Aside from watering it into the soil, it can also be used as a foliar application. My recommendation is to apply it in the morning. This is because plants open their foliage pores in the morning to drink in mildew making it much more effective than applying it during the day or in the evening.

Another great addition to your potting shed shelf since this feed is not only applicable for zucchini but can be used as a fertilizer for other vegetables as well. 

How to use: Mix 1/8 cup of fertilizer liquid with 1 gallon of water then water the soil liberally. Alternatively, drench foliage. Apply every two weeks.

4. Jobe’s Tomato Fertilizer Spikes 6-18-6

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Pros

• Continuous nourishment for 8 weeks
• No wasteful runoff
• Mess and odor-free fertilizing

Cons

• Maybe at a higher price point than others

Jobe’s spikes are essentially slow-releasing, timed fertilizers. They can provide a single plant with enough fertilization for two months.

This doesn’t mean that you’ll overfertilize your zucchini – spikes release their granules slowly, ensuring that there’s never too much or too little fertilizer for the plant.

You can just stick one spike next to one plant and leave it for the rest of the season as the spike slowly provides it with enough nutrients. There are 18 spikes in this pack, which should be enough for a small zucchini.

5. Osmocote Flower & Vegetable Fertilizer 14-14-14

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Pros:

• Granular capsules that provide slow-release fertilizing
• Can be used on a variety of vegetables and flowers
• Feeds plants for up to four months 

Cons: 

• Overuse can lead to fertilizer burn

The evenly balanced 14-14-14 NPK ratio in these slow-release granules from Osmocote is just a bit stronger than the ideal 10-10-10 ratio for zucchini, but I’ve never found it to harm my plants. Just remember to avoid applying too much of it and always read the label before using it. 

Bear in mind that this fertilizer releases its nutrients more quickly during warmer periods – something to keep in mind when it comes to summer fertilization. I prefer to apply it early on in the growing season so that the nutrients have begun the process of dispersion when the plants are young and tender.

This is a great potting shed staple for allotment growers as it can be used with a variety of vegetables and flowers, feeding them for up to 4 months at a time.

How to use: Water the soil before using the handy lid-top dispenser to sprinkle the required amount over the soil around your plants. Water will start dissolving the capsules and the nutrients will release thereafter. 

Because a single application can last up to four months (depending on how much fertilizer you used), this eliminates the need for reapplication.

6. Jobe’s Plant Food Vegetables & Tomato 2-5-3

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Pros: 

• Additional phosphorous encourages flower and fruit production
• Improves soil health and protects against disease
• Contains calcium to support common deficiencies

Cons: 

• We May need more applications to support heavy feeding requirements

This slow-releasing fertilizer was made specifically for tomatoes but is ideal for other flowering fruit and vegetable plants such as zucchini and squash. 

It contains bone meal which is a natural source of phosphorus and calcium, the latter of which can help with calcium deficiency which is a commonly occurring problem with zucchini plants that can lead to flower or leaf rot. 

Another important aspect of this fertilizer is Jobe’s patented BioZome formula. This is a combination of healthy bacteria and fungi that improves soil quality and develops resistance to diseases and pests.

Although it doesn’t follow the 10-10-10 NPK ratio that zucchini benefit from, I found that following the manufacturer’s recommendations of applying it once every five weeks still ensured a healthy, bumper crop of fruit on my zucchini plants.

How to use: Apply every 4-6 weeks by sprinkling in the soil around the base of the plant. Measurements vary depending on whether your plant is a container of ground planted. Gentle enough to use for new plantings by sprinkling into the planting hole.

7. Jack’s Classic All Purpose Fertilizer 20-20-20

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Pros

• Optimal nutrition for bud production and green foliage
• Dissolves faster and cakes less than other top brands

Cons

• It May give off an earthy odor 

Here’s a water-soluble option now from JR Peters. It’s a great fertilizer as it contains a powerful micronutrient package that includes – most noticeable – the micronutrient calcium, which can help with dreaded and oh-so-common calcium deficiencies in zucchini plants.

It also contains magnesium, which can improve feeding results for lots of edible fruit and vegetable plants. In fact, according to the manufacturer, this fertilizer was designed with zucchini in mind, but it’s also great for tomatoes, peppers, cucumber, eggplant, and squash.

As you’ll immediately notice, this fertilizer packs a much meaner punch than the standard 10-10-10 ratio. This means that you should apply it with caution to avoid overfertilization.

I recommend using this after you’ve conducted a soil test that shows depleted and nutrient deficient soil. Its high NPK ratio will be too powerful for fertile and nutrient-rich soil.

How To Use: For new plantings, add ½-1 cup per hole, mix into the soil, and water in the well. Apply once per month during the growing season.

8. Miracle-Gro Shake ‘N Feed Vegetable Fertilizer 10-5-15

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Pros

• Dispense directly from the container
• Only requires one application every 3 months
• Improves soil condition and contains calcium

Cons

• Can burn if used excessively 

The granular fertilizer from Miracle-Gro on the list is ready to use right out of the container and will keep your zucchini fed for up to three months. In addition, it is rich in calcium to protect against flower rot.

What I also love about this fertilizer is the inclusion of an array of natural ingredients that feed the microbes in the soil. Microbes play a vital role in stimulating plant growth by producing hormones that are beneficial to healthy growth and development.

I recommend using this just before the growing season kicks off. It’s a great way to ensure that soil is equipped with the nutrients required to support new plant growth. 

How to use: Suitable for ground-planted and container-grown vegetables. Scatter the required amount in and around your vegetables once every 3 months during the growing season.

9. Miracle-Gro Performance Organics Plant Nutrition 11-3-8

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Pros:

• Provides an instant boost of nutrients
• Supports healthy foliage and root growth
• Easy to apply liquid fertilizer that covers large areas

Cons: 

• We May need to supplement phosphorous at the flowering stage

Not dissimilar in NPK ratios to the Miracle-Gro granules that I have featured above, however, this is a liquid fertilizer. It is easy to administer but with the added bonus that it instantly provides nutrients to your plants. 

I use this right from the start of the growing season when my zucchini plants need a head start on foliage growth due to the high nitrogen content. 

It uses soy protein as its source of nitrogen – soy protein is highly soluble, making it easy for plants to take in. Bonemeal is also a key ingredient in this fertilizer It’s a source of calcium and phosphorus, which means it can be used to treat calcium deficiencies in zucchini plants.

It also contains a healthy ratio of potassium. This is superb as the season progresses for aiding root strength and development and for fending off pests and diseases.

How to use: Combine one gallon of water with 2 scoops of fertilizer to cover 10 square feet of soil.

How to Fertilize

The two most important elements of fertilizing zucchini (and any other plant, for that matter) are the rate and timing of fertilization and the amount of fertilizer you use.

If you use too much fertilizer, you’ll overfertilize your zucchini. On the other hand, if you don’t use enough fertilizer, you’ll under fertilize it.

Great news for you – zucchini doesn’t have extreme requirements for fertilization, so it’s generally easy to fertilize it and overfertilization shouldn’t be a problem.

Avoiding Overfertilizing

Application is generally recommended at a rate of up to 4 pounds of 10-10-10 fertilizer per 100 square feet for zucchini. The exact amount of fertilizer depends on the exact size of the areas you have zucchini planted in. For example, if you only have 50 square feet of zucchini (which is usually enough for one family), you only need 2 pounds of granular fertilizer.

During the second fertilization, which usually occurs in the summer, you only need half a cup of the same fertilizer – spread that around all your plants.

How to Apply Granular, Liquid, and Spike Fertilizers

These are the three types of fertilizers, and each one has its positives and negatives.

To apply granular fertilizer, you should water the plants plentifully a few days beforehand to soften the soil as you’ll have to dig in. To fertilize, spread the granules around the soil (up to six inches in diameter, two inches into the ground), cover them with soil, and water them.

Liquid fertilizers require much less work, as you only have to make the solution according to the instructions on the label. This usually means that you have to mix a bottlecap or two bottlecaps of fertilizer with a few liters (or gallons, depending on the amount you’re making) of water.

After that, all you have to do is pour it out.

Spikes are the easiest to apply – simply stick them next to each plant and let the granular fertilizer roll out as the plant needs it.

When to Fertilize

You should fertilize your zucchini as soon as the first seedlings grow out of the soil (if you just planted it). This usually means fertilizing it heavily in the spring (the 4 pounds per 100 square feet rule).

After that, you’ll only need to fertilize it once again in the summer. Specifically fertilizing it when the plant begins to bear fruit in the summer (half-a-cup rule).

Aside from those two occasions, you don’t need to fertilize zucchini until next year.

How Often to Fertilize

Zucchini needs to be fertilized twice per season – anything more than that is excessive and it will lead to overfertilization.

A Word About Fertilizing Zucchini Flowers

A common issue with growing zucchini is where your seemingly happy and healthy plant develops flowers that do not then develop into a fruit. This occurs when there aren’t enough flowers of both sexes on the plant and/or if there aren’t natural pollinators in your garden.

Female flowers have immature fruit at the base and will only bear fruit after being pollinated (usually by bees) with the pollen from the male flowers. 

Zucchini plants often produce more male flowers than female during the growing season. However, if you have a plant that’s flowering but not developing fruit, it’s likely the result of female flowers that haven’t been pollinated. 

So, unless your garden is a habitat that attracts bees, you’re going to have to pollinate the zucchini yourself.

Many people use the terms fertilization and pollination interchangeably. Professionally, however, pollination is the process of creating plant offspring (it’s basically planted insemination), while fertilization is supplying plants with crucial nutrients.

Fertilizing Zucchini Final Thoughts

Zucchini isn’t a hungry plant and you only need to fertilize it twice – once in the spring, and once during the summer. Just like all other plants, it’s susceptible to overfertilization, so you have to make sure not to apply too much.

The recommended NPK ratio for zucchini is 10-10-10, but it is perfectly acceptable to use an evenly balanced feed and adjust the proportions and number of times you apply fertilizer thereafter if required. When choosing a fertilizer, it’d be smart to find a fertilizer with calcium, as the soil can easily develop a calcium deficiency.

Best Slow-Release Granules

Burpee Natural Granular Organic Food 4-4-4

Slow-release granules containing an even balance of NPK – just how zucchini plants prefer.

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So now it’s over to you. What will you choose? Slow-release granules from Burpee that provide nutrients for up to 3 months during the growing season? Or, the promise of a 100% natural and organic ingredient list and the ability to improve soil conditions, then go for Dr Earth with a nutrient balance in the same quantities.

Best Organic Fertilizer for Zucchini

Dr. Earth Organic All Purpose Fertilizer 4-4-4

A perfectly balanced organic fertilizer. Gentle enough even for new plants and suitable for use throughout the growing season.

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Alternatively, if it’s a liquid feed you need – and this is the ideal option for container-based plants that tend to leach nutrients quicker – then choose Neptune’s Harvest Liquid feed. 

Best Fertilizer for Zucchini in Pots

Neptune’s Harvest Veg Fish Fertilizer 2-4-2

An organic, liquid concentrate fertilizer that will provide zucchini plants with an instant boost as well as improve the soil when prone to nutrient deficiencies.

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Fertilizer Requirements for Zucchini FAQ