You already know your cucumber plants need lots of nutrients to produce crispy, delicious fruits. Fertilizer is the way to deliver those nutrients, but what’s the best one to use? I wondered the same thing when I first started gardening, and I’ve gone through a fair bit of trial and error over the years.

I’m glad to say I’ve settled on the ones I believe are the best fertilizer for cucumbers, and I’m going to share those with you today. We’ll cover the roles of nitrogen, phosphorus, and potassium, as well as the different types of fertilizers and DIY options.

Let’s get going!

Nutrient Requirements for Cucumber Plants

For some reason, I didn’t grasp this for a long time: Mineral content in vegetables and fruits directly affects their flavor. The fruits/veggies with the highest nutrient levels taste the best and are usually more vibrant in color too.

All plants need 16 essential elements to live. Three of these- oxygen, carbon, and hydrogen- are absorbed through the air. The other thirteen are soil-based nutrients, and they’re divided into two categories:

1. Macronutrients: Nutrients needed in a higher dose
2. Micronutrients: Nutrients needed in a smaller dose (also called trace elements)

These are the six macronutrients:

1. Nitrogen
2. Phosphorous
3. Potassium
4. Magnesium
5. Calcium
6. Sulfur

These are the seven micronutrients:

1. Boron
2. Molybdenum
3. Manganese
4. Iron
5. Copper
6. Chlorine
7. Zinc

The three primary nutrients crucial for growing cucumbers are nitrogen, phosphorus, and potassium. These are the ones you’ll see listed in a fertilizer’s NPK analysis. Here’s why they’re important:

• Nitrogen (N). Nitrogen is essential for the development of cucumber leaves and stems. I think of it as “the green mineral” since it’s a key component of chlorophyll, but it also contributes to proteins and certain plant hormones. However, too much nitrogen can result in excessive foliage growth at the expense of flowers and fruits. So you need to strike the right balance here.
• Phosphorus (P). Phosphorus aids in cell division and the development of the plant’s growing tip, ensuring healthy plant growth. It’s also vital for root development, flowering, and fruiting in cucumbers. Too much phosphorus can lead to stunted growth, weak root systems, and limited cucumber blooms. Plus, excessive phosphorous in gardens runs off into local waterways, leading to harmful algae overgrowth.
• Potassium (K). Potassium facilitates the formation and movement of starches, sugars, and oils throughout the plant, and it also enhances the plant’s overall health and disease resistance. But here again, you don’t want too much- it can cause difficulty absorbing nitrogen and phosphorus.

The NPK analysis represents the concentration, shown as a percentage, of each nutrient in the formula:

This one is a 12-5-7 formula so there’s 12% nitrogen, 5% phosphorous, and 7% potassium.

A balanced fertilizer contains equal amounts of nitrogen, phosphorous, and potassium, like this 4-4-4 formula:

Types of Fertilizers for Cucumbers

You’ve got some options when it comes to cucumber fertilizer type.

In my mind, I break them down into a couple of categories:

• Organic
• Synthetic

And in each of those categories, there are two different formulations:

• Granular
• Liquid

I think it’s important to understand the details of each of these types/formulas, so let’s break them down a little more.

Organic Fertilizer vs Synthetic Fertilizer

I’ll start with organic vs. synthetic fertilizer types.

Organic Fertilizer

Organic fertilizers are made from ingredients found in nature. A couple of examples of ingredients I often see include:

• Worm castings
• Seaweed
• Aged processed manure
• Fish emulsion

Personally, I always choose an organic fertilizer for any edible crops I’m growing. I’m a little more lenient if I have to be when it comes to ornamental plants. But even then, organic is truly the best option if you’re able.

Synthetic Fertilizer

Synthetic fertilizers, also known as chemical fertilizers, are created from inorganic compounds and offer precise nutrient ratios to plants. In short, synthetic fertilizers are specifically developed to achieve a goal or address a problem, and they’re incredibly effective for the most part.

But I advise avoiding synthetic fertilizers, especially on vegetables. The chemical ingredients may have a detrimental effect on the environment and do not contribute to soil texture or long-term soil fertility. If you choose to use synthetic fertilizers for your cukes, it’s important to follow the application instructions carefully to minimize any potential concerns.

Granular Fertilizer vs Liquid Fertilizer

Now let’s address the question of granular and liquid formulations.

You’ll find both formulations in both organic and synthetic types. In my opinion, this is purely a matter of personal preference- I’ve used both successfully in the past.

Granular Fertilizers

Granular fertilizers come in pellets, flakes, and coarse powder.

They’re a popular choice for gardeners because they offer slow-release nutrients, are simple to apply simple to apply, and are cost-effective when purchased in bulk. This is the formulation I typically use because it’s cheaper, easy to use, works for a long time, and stores well.

Liquid Fertilizers

Liquid fertilizers are made up of nutrients suspended in a water-based solution. You can use liquid fertilizer to target the roots through the soil or as a foliar spray to direct absorption through the leaves.

The nutrients in liquid formulas are already dissolved, so your cucumbers can rapidly absorb them. If you think your cukes are suffering from a nutrient deficiency, this is the formulation you want since it works so quickly.

But liquid fertilizers do require more frequent applications than granular ones, and they tend to be more expensive. Plus, the liquid suspension is more vulnerable to breaking down over time, so they lose potency in storage.

Best Fertilizer for Cucumbers: Top 5 Choices

Now that you understand the types and formulations you can use to fertilize cucumber plants, let’s get down to the specific products. I chose these products based on my own experience with them, features, benefits, and drawbacks. Options are good, and these are the cucumber fertilizers I believe are the best!

1. Jobe’s Organics All-Purpose Granular Fertilizer

• NPK: 4-4-4
• Best time for use: All season long
• Fertilizer type: Organic
• Formula type: Granular
• Made in USA: Yes
• Price: $

This granular formula from Jobe’s Organics comes in as my top pick for the best cucumber fertilizer. I use it in my garden, and I’ve been happy with the results. With a balanced NPK, I find that my plants do well with routine applications all season long.

As a granular formula, it’s easy to apply and feeds your cucumbers for a long time. It also contains Jobe’s Biozome, a Jobe’s-exclusive blend of beneficial microbes that nourish your plant and build soil long-term health.

Another nice thing about this fertilizer is that it’s made by a popular and reputable brand, Jobe’s Organics. While you certainly can order it online, you should also have no trouble finding it at your local garden center or big-box store.

2. Dr. Earth Home Grown Tomato, Vegetable & Herb Fertilizer

• NPK: 4-6-3
• Best time for use: All season long
• Fertilizer type: Organic
• Formula type: Granular
• Made in USA: Yes
• Price: $$

This was a very close second choice for me. I really like this fertilizer, and I’ve had nothing but good results with all Dr. Earth products. But Home Grown fertilizer comes in at #2 because it can be hard to find on store shelves or at a good price online.

This vegetable and tomato fertilizer has a flaky texture that breaks down more quickly than larger pellets. I’ve found that it’s easy to apply around plants and scratch into the soil surface. Dr. Earth uses ingredients that are certified human-grade and feed-grade, so this formula is safe for people and pets.

3. Fox Farm FX14091 Big Bloom Liquid Concentrate Fertilizer

• NPK: 1-3-7
• Best time for use: Flowering and fruiting stages
• Fertilizer type: Organic
• Formula type: Liquid
• Made in USA: Yes
• Price: $$

Once your cucumbers have reached the flowering stage, switching to a fertilizer with higher phosphorous and potassium can help you get the highest possible yields. And Big Bloom fertilizer from Fox Farm really gives its synthetic rivals a run for their money.

Fox Farm uses rock phosphate to supply phosphorous, which is a form that’s readily absorbed by plants. The formula also contains bat guano, Norwegian sea kelp, and worm castings to provide lots of nutrients.

Even though it’s powerful, this is also a gentle formula that you can use on your cucumbers frequently without the risk of burns.

4. Espoma Organic Tomato-Tone 

• NPK: 3-4-6
• Best time for use: Flowering and fruiting stages
• Fertilizer type: Organic
• Formula type: Granular
• Made in USA: Yes
• Price: $

Products labeled as tomato fertilizer are usually just right for cucumbers too- and this organic formula from Espoma is my top choice.

With a lower ratio of nitrogen compared to phosphorous and potassium, this fertilizer is best suited to your cucumbers’ later growing stages. Although with 3% nitrogen, you can also use it all season long if you choose.

In addition to the NPK, Espoma also included an 8% concentration of calcium. Calcium helps prevent your cucumbers from developing blossom end rot- always a discouraging thing to see after nurturing your cukes to the point of fruiting.

5. Worm Tea Fertilizer Liquid

• NPK: 1-1-1
• Best time for use: All season long
• Fertilizer type: Organic
• Formula type: Liquid
• Made in USA: Yes
• Price: $

Fertilizer tea is the perfect way to add nutrients to your soil gently, and Worm Tea from PetraTools Solutions is the brand I recommend.

This liquid fertilizer tea is made from worm castings, which have earned the rightful reputation as a garden soil super booster. It has a low NPK, but the main benefit is the high concentration of beneficial bacteria it adds to the soil. Research studies show that these friendly microbes produce nutrients to nourish your plants, so it’s a totally natural fertilizer that actually builds your soil’s health for the long term.

How to Use Cucumber Fertilizers

The timing and techniques you use when you fertilize cucumbers play a crucial role in their growth and yield. Proper fertilization not only ensures your plants receive the nutrients they need but also helps prevent problems like over-fertilization and nutrient deficiencies.

In this section, I’m going to cover timing and techniques for fertilizing at different stages of cucumber growth, from seedlings to the flower and fruit production stage.

1. Young Seedlings

Did you know that the cucumber seed itself contains all the nourishment a baby plant needs for the first few weeks of life? It’s true, and applying fertilizer- even a gentle one- too soon can overwhelm or be caustic to a tiny cucumber sprout.

Wait until your cucumber seedlings get established before fertilizing them- two sets of true leaves is a good benchmark. After that, give a 1/2 strength dose of liquid fertilizer (it’s easier to dilute reliably) every two weeks to provide them with a steady supply of nutrients for optimal growth.

2. Transplants

If you’re transplanting cucumber seedlings, I recommend waiting a week to 10 days to apply fertilizer. This gives the plants time to acclimate to their new home before potentially stressing them out with excessive nutrients to process.

Either granular or liquid fertilizer is a great choice here- just be sure to follow the manufacturer’s instructions for proper application and dosage. Then, water the soil thoroughly to help the nutrients reach the plant’s roots and promote healthy growth.

3. During Growth

While the cucumber seedling is young, it’s in the vegetative phase, meaning that the plant is focusing heavily on leaf and stem production.

Nitrogen is key for this, so a fertilizer with a higher nitrogen component is appropriate. In my experience, a balanced formula that you use all season long does a good job of supporting your plants and producing a moderate harvest. That’s what I do- I’m content to have enough cukes to enjoy fresh, and I like to keep things simple.

Whether you choose a granular or liquid formula, follow the package directions for dosing.

4. Flowering and Fruiting

Cucumber blossoms and cucumber fruits are two steps that are so closely related that I’ll count them as one.

During the flowering and fruiting stage, your cucumber plants require a different balance of nutrients for optimal yields. At this stage, you can either continue with your balanced formula or switch to a low-nitrogen fertilizer with high phosphorus and potassium to promote healthy fruit development and prevent excessive foliage growth.

Apply the fertilizer every two weeks to ensure your cucumbers receive the nutrients they need to produce an abundant harvest of crisp, flavorful cucumbers.

Soil Testing and pH Considerations

In addition to choosing the right fertilizer for your cucumber plants, the soil’s underlying nutrient content and pH level also matter. Let’s talk about the importance of soil testing and maintaining the ideal pH level for growing cucumbers.

Soil Testing

A soil test is a good idea to make sure you don’t overdo it with certain nutrients, which can throw off absorption of other elements can cause long-term issues. And in some situations, your soil could be severely depleted in key nutrients, needing a bigger correction than a standard fertilizer offers.

You can either use a simple soil test that shows the pH and key macronutrients (nitrogen, phosphorous, and potassium) or a comprehensive test that analyzes the full nutrient profile. Some tests also assess heavy metals.

You can get a simple soil test– they’re easy to use and inexpensive. For a comprehensive soil test, you’ll need to send a soil sample to a lab for analysis. I recommend My Soil or SoilKit– both are simple and don’t cost too much. For a truly thorough test, contact your local extension office for state university lab testing.

Ideal pH Level

Like most veggies, cucumbers thrive in a pH range of 6.0-7.0, which allows for optimal nutrient absorption and overall plant health. If your soil’s pH is outside this range, your plants may struggle to absorb the nutrients they need.

Most soil tests will show the pH level.

To adjust the pH level of your soil, you can add lime or sulfur, depending on whether your soil is too acidic (add lime) or too alkaline (add sulfur).

Using Cucumber Fertilizers in Different Growing Environments

While cucumbers growing in any environment need many of the same things, there are some differences in the fertilizing routine to keep in mind.

1. In-Ground Gardens

Cucumbers growing right in the ground have the benefit of reaching their roots deep into the soil and soaking up all those good naturally-occurring nutrients. So while they’ll still appreciate some supplemental nutrients, this is probably the growing environment where you’ll be reaching for the cucumber fertilizers the least.

As long as you start out with compost amended soil, using fertilizer every 4 weeks or so should be enough to keep your cukes healthy. However, a soil test is a great idea before planting- that way, you can tell if the nutrient profile or pH in your garden soil is off and address it right away.

2. Container Cucumbers

Growing cucumbers in containers requires more frequent fertilization compared to those grown in the ground for a couple of reasons:

• Nutrients in pots get flushed out of the soil with every watering
• Cucumbers take a lot of nutrition to grow, and they quickly deplete soil nutrients when they’re growing in a small volume of potting mix.

So make fertilizing a regular part of your care routine for container cukes- every two weeks with a water-soluble formula.

3. Raised Bed Cucumbers

Raised bed cucumbers are somewhere in the middle of in-ground and containers. There’s a larger soil volume, which helps hold onto nutrients for longer, but it’s still not the same as regular garden soil.

I’ve got some cucumber plants in a 4×8 metal raised bed:

I recommend applying fertilizer every 3-4 weeks. This will help ensure your plants receive the nutrients they need to produce an abundant harvest of delicious cucumbers.

4. Greenhouse Cucumbers

Treat greenhouse cucumbers in much the same way as container cukes since it’s likely that you’ll be growing them in large pots. I recommend starting out sparingly since a greenhouse is such a tightly controlled environment. Give your cukes fertilizer every four weeks, then monitor your plants and tailor your routine as needed.

Signs of Over-Fertilization and How to Correct It

In my experience, getting a little over-eager with cucumber fertilizers can cause more damage than erring on the stingy side. Too much fertilizer can cause a range of problems, from stunted growth and yellowing leaves to reduced fruit production. You don’t want that!

My personal advice is to stay on the conservative side with fertilizer- especially commercial formulas. Most synthetic fertilizers contain mineral salts, which can cause chemical burns to plant roots in high enough concentrations. I find that it’s harder to overdo it with organic or natural fertilizers.

Key signs of ever-fertilizing are browning around the leaf edges, where the plant material is thinnest. Continued over-exposure can cause wilting/drooping, poor growth, yellowing leaves, and a whitish crust on the soil.

To correct over-fertilization, flush excess nutrients from the soil by watering deeply. If your cucumbers are in a pot, you may have to repeat the flush a couple of times. Then stop all fertilizing for at least a couple of weeks, then resume with a lower dose. And always make sure to water thoroughly every time you apply fertilizer!

DIY Fertilizer Options for Cucumbers

In addition to commercially available fertilizers, there are several DIY cucumber fertilizers. These are fantastic ways to use natural ingredients to enhance your garden, and best of all, they’re often materials that you might otherwise throw away.

Some popular DIY fertilizers include:

• Compost
• Worm castings
• Coffee grounds
• Eggshells
• Fish emulsion
• Epsom salt
• Wood ash

Each of these options offers unique benefits and nutrient compositions, allowing you to customize your fertilization plan for healthy, happy, and eco-friendly cucumbers.

Final Thoughts

I hope this post has answered your questions about what makes the best fertilizer for cucumbers and how to use them in your garden.

The choice is yours when it comes to organic vs. synthetic, and granular vs. liquid- from what I’ve learned, how you apply the fertilizer matters most. Just start out carefully, assess how your cucumbers respond and go from there!

I’d love to hear from you! Is there anything you’re still wondering about regarding cucumber fertilizer? Or maybe there are some tips you’ve learned along the way that I didn’t include here. Whatever’s on your mind, somebody else can likely learn from it, so please feel share in the comments!