5 Best Fertilizer for Cucumbers | How & When to Use

The humble cucumber is one of those easy-to-grow crops that, with the right fertilizing strategy, you could end up sharing with the whole neighborhood. Another benefit is the mouth-watering flavor and texture they add to salads, sandwiches, and even just on their own with a bit of sour cream dip. 

To achieve optimum quality, these vined gourds thrive when fertilized with a moderately balanced NPK. Though cucumbers are known to be heavy feeders, they don’t require as much nitrogen as other crops might. The best fertilizer for cucumbers will be a little heavier in phosphorus and potassium (like a 3-4-6) to encourage abundant blooms and juicy fruit. 

I’ve gathered a comprehensive list of the 5 best fertilizer for cucumbers. Each one is a little unique but each one is greatly effective for producing a large and tasty bounty. Which we’ll discuss in a moment. 

Choosing the Best Fertilizer for Cucumbers 

A quality fertilizer promotes bigger cucumbers and a higher yield. An added bonus would be one that nourishes your plants and improves soil fertility at the same time. 

In this case, “quality” means one with the most effective NPK combination. As well as supporting micronutrients, trace elements, and beneficial bacteria. These bacteria actually break down nutrients and convert them into a form that’s more easily absorbed by your plants. 

N-P-K Cucumber Fertilizer Ratio 

A fertilizer’s NPK is displayed as three numbers on the label. These indicate its proportions of nitrogen, phosphorus, and potassium. For example: A 3-4-6 NPK contains 3% nitrogen, 4% phosphorus and 6% potassium.

When grown in pots, a 2-3-6 can provide all that your cucumbers need in their limited environment. In the ground, cucumbers would benefit from a 5-10-10. Or perhaps a 20-20-20, if your soil needs a little boost too. 

Granules Vs Liquid Fertilizer 

Deciding on an application method is simply a matter of what works best for you and your lifestyle. Liquid nutrients are quickly carried to the roots, allowing for immediate uptake. They can keep crucial pH levels balanced, too. But, caution is recommended, as over-feeding could lead to root burn.

Concentrated granules are slow-releasing and provide a consistent flow of nutrients for several months at a time, saving you time and effort. 

Liquid Fertilizer 

Cost-effective and time-saving liquids allow for simultaneous watering and nourishment and give you control over how much is applied and when. Vital nutrients flow directly through the soil to the roots. Which is especially beneficial for those living with shorter growing seasons. Liquid options are also typically less expensive. 

Granular Fertilizer 

As a slow-release choice, I find granules to be time-saving for you, the grower. Highly concentrated, they provide consistent nourishment for several months at a time. If applied prior to rainfall, no watering is needed for activation and is less likely to leach into nearby water sources, preventing contamination.  

Organic Cucumber Fertilizer 

For purely organic growing, nothing provides a more fertile, slow-releasing option than well-rotted compost. Chock-full of those beneficial microbes I spoke of earlier, it’s a great NPK source with trace minerals that won’t overwhelm your plants. While also improving moisture-retaining and drainage properties in sand or clay-based soils.

Worm castings are another great choice for an organic, slow-release fertilizer that has enough gentle nitrogen and trace elements to satisfy your cucumbers. 

Ideal pH for Cucumbers to Grow 

Cucumbers prefer a pH range of 6.0 – 7.0. Anything above that (overly alkaline) will block access to nutrients you’re providing. A pH that is too low (overly acidic) will render your plants vulnerable to the effects of damaging heavy metals in the soil which will stunt photosynthesis. Cucumbers can tolerate the low or high end of this range as long as the soil is fertile and well-draining.  


5 Best Cucumber Fertilizer Reviews 

I’ve done some extensive testing and research, including feedback from cucumber growers across the gardening and retail spectrum. I’ve covered what performed best, which was easiest to use and which had the best value for money. Read on to find out which best fertilizer for cucumbers product will suit you best.


1. Espoma Garden-Tone | Plant Food, Natural & Organic Fertilizer 3-4-4

Espoma’s Garden-Tone

Espoma’s Garden-Tone is a patented, slow-release granular formula that is perfect for cucumbers and other crops that need to be grown in nitrogen-rich soil.

This is a slow-release formula that allows you to apply the first application in spring to new corn plant seedlings and then repeat monthly thereafter throughout the growing season. It’s a brand I’m always happy to trial in my vegetable patch and am never disappointed with the results. In fact, I trialed this as a corn fertilizer at the same time as trying it out on my cucumbers.

It is lower in nitrogen than some others I used so it doesn’t overwhelm my plants. Yet, introducing these exclusive Bio-Tone microbes really helps to disburse nutrients into the soil. The outcome is plants that grow strong, robust roots and stalks, and a plentiful yield of disease-free crops.

How To Use: Mix the recommended amount into the soil prior to planting or apply to seedlings 7-10 days after planting. Repeat monthly from May to August. 

Customer Reviews: Cucumber growers are reporting results within just 1 week of application and surprising bumper crops after a full season of using this organic product. Awarding Espoma’s Garden-Tone 4.7 out of 5 stars and my pick for best buy. Check the latest Espoma Garden Tone price here. 

Pros      

  • Organically-grown high yields
  • Results after just one week

Cons

  • Organic odor may be attractive to pets

2. Down to Earth | Organic Vegetable Fertilizer 4-4-4 

Down to Earth Organic Vegetable Fertilizer

My second pick is from Down-to-Earth. This equal-ratio vegetable feed is formulated to work with compost-amended soil. I found this to be the perfect complement to any organic matter compost or mulch that I add to the soil around my crops.

It’s a granular formula that works well either sprinkled directly onto the soil or used as a fertilizer tea and it is mild enough to use frequently without any fear of root or foliage burn. Perfect for the heavy feeding requirements of cucumber plants.

The end result is vibrant foliage and large, crisp cucumbers in bumper crop proportions. See prices for Down To Earth Vegetable Garden Fertilizer here.

How To Use: Apply ½ cup per sq foot of growing area and work into the top 3” of soil. Repeat twice per month throughout the growing season.

Customer Reviews: Gardeners across many review platforms are raving about the wonderfully organic results they’ve seen using this product. And without the typical odor associated with organic products. Calling it “their secret to success”. 4.7 out of 5 stars.

Pros      

  • Equal-ratio NPK for use in composted soil 
  • No harsh odor

Cons

  • May be at a slightly higher price point than others 

3. Dr. Earth Organic | Tomato, Vegetable & Herb Fertilizer 4-6-3

Dr. Earth Organic | Tomato, Vegetable & Herb Fertilizer

This next organic option is from Dr. Earth and has proved effective and versatile when tested as both a top dressing and a water-soluble tea. Infused with probiotics plus seven beneficial microbiotics, my slicing cucumbers were able to metabolize nutrients better, resulting in twice the fruit size and yield. 

This is the option for your cucumber plants if they are already planted in nutrient-rich organic soil that you have taken the time and effort to compost and mulch prior to planting. With the slightly higher ratio of phosphorous in this fertilizer expect a healthy disease-free crop and plenty of growth throughout the season. Check prices for Dr. Earth Organic Tomato, Vegetable & Herb Fertilizer here.

How To Use: New plantings: add 1 ½ cups to soil before planting. Established plants: apply ¾ cup for every 10 sq ft of growing area. Repeat every 2 months. 

Customer Reviews:  Consumers are reporting that Dr. Earth’s feed is great value for money. Putting it at the top of their “favorites” list. In small gardens, it can last for several growing seasons and the results are far better than other pricier options. Awarding it 4.6 out of 5 stars.

Pros      

  • Great value for money
  • Probiotics and seven beneficial microbiotics

Cons

  • Animals may be attracted to organic smell 

4. Down to Earth | Organic Vegan Fertilizer Mix 3-2-2 

Down to Earth | Organic Vegan Fertilizer

Another goodie from Down To Earth now and this time, one for vegan and vegetarian organic gardeners. It contains no animal products or animal by-products in this formula and instead is made up of vegetable and plant-based nutrient-rich ingredients such as alfalfa meal, canola meal, and soybean meal.

It is the careful blend of plant-based ingredients that provides this nitrogen-rich blend fertilizer. I tried it on some pickling cucumbers in an area I haven’t heavily composted. Not only did I get a surprising number on each plant, but the flavor and crispness of each were far more distinct than without. Check out Down to Earth Organic Vegan Fertilizer from Amazon.com

As you may have come to expect from an organic feed, this one has an odor this is highly attractive to dogs. Mine seemed to love it.

How To Use: Vegetable beds – apply 2.5-5 lbs per 100 square feet and thoroughly mix into the top 3″ of soil. New transplants – add 1-2 tbsp per hole, mix into soil and water in well. Repeat once per month during the growing season.

Customer Reviews: Gardeners are using this on everything from veggies to kitchen herbs and loving the purely organic results. Great value for money. 4.7 out of 5 stars.

Pros      

  • Suitable for vegan gardening – Organic results from a purely plant-based products
  • Versatile use on any nitrogen-hungry plant

Cons

  • Animals may be attracted to organic smell 

5. Miracle-Gro Shake ‘N Feed | Tomato, Fruit & Vegetable Plant Food 10-5-15

Miracle-Gro Shake 'N Feed | Tomato, Fruit & Vegetable Plant Food

Miracle-Gro Shake n’ Feed contains specially formulated micronutrients for your plants and an array of natural ingredients to feed the microbes in the soil. If that wasn’t enough this formula also contains extra calcium. All of this combined helps to stimulate plant growth and encourage higher quality cucumber crops with a longer shelf life.

This is a good option to use right at the start of the growing season even before the growing season has begun especially in soil that is slightly less than perfect. That way, the soil is primed and nutrient-rich ready to support new plant growth when it starts.

I have found that find this fertilizer can be used in my garden borders and containers where the soil was less-than-fertile. Check out Miracle-Gro’s Shake n’ Feed at Amazon.com

How To Use: Apply the recommended dosage directly to dry soil and mix into the top 3 inches. Water thoroughly and re-apply every 3 months. 

Customer Reviews: Gardeners, who used different feeds for different plants, really appreciate the ease of use and versatility of this product. And the new calcium-added formula is definitely a bonus. 4.7 / 5 stars.

Pros      

  • Versatile enough for use with all garden vegetables
  • New calcium-added formula for higher quality crops

Cons

  • Results may vary in nitrogen-poor soil

Fertilizing Cucumbers Indoors and Outdoor 

Provided that they have adequate sunlight, warmth, soil content, and nutrients, these climbers can grow quite nicely indoors.  A milder NPK, like a 2-3-6, will accommodate the nutrition needs of potted cucumbers. While cutting down on the risk of overfeeding.

In outdoor veg patches, these plants will be able to spread out and become bigger. Requiring the need for a slightly higher NPK ratio like a 3-4-6 to satisfy their needs. 

Cucumbers in Pots and Containers 

Potted plants need frequent watering, which often results in soil and nutrients leaching out. A slow-release option can be sprinkled around your plant’s base to be administered in small doses with every watering. Greatly minimizing the risk of plant burn, often associated with liquid fertilizers. 

Cucumbers in Greenhouse 

In greenhouses, plants are more easily managed because they have direct yet controlled access to environmental needs like bright sunshine, warmth, and fresh air. These factors will naturally stimulate robust and vigorous growth. The right fertilizer will help support that for a higher yield of lovely cucumbers. 

How to Fertilize Cucumbers 

The best fertilizer for cucumbers will result in a bountiful harvest when the NPK is lighter on nitrogen and your plants are consistently fed through to autumn. 

If starting from seed, the second set of leaves will signal when to start adding a bit of fertilizer. This can continue until around a month before harvest so all the plant’s energy will go to ripening existing cucumbers instead of triggering new growth. 

How Often to Feed Cucumber Plants 

Feeding frequency will depend on the brand and application type of the fertilizer you choose. Slow-releasers recommend fewer applications over the course of a growing season. Perhaps, once every 1-3 months. Water-soluble methods are faster acting and require weekly applications if growing in pots. 

Over Fertilizing Cucumbers 

Too much fertilizer can easily lead to root burn and plant failure, especially for cucumbers grown in pots. At the very least, over-fertilizing will stimulate the growth of lots of lush foliage but no flowers. Which means no cucumbers. Success comes from consistent, measured applications over time. 

When to Fertilize Cucumbers 

With cucumber seedlings, you can add some fertilizer to the bottom of the hole before adding your plant. Once flowers appear, it’s safe to start the second stage of application, based on the brand’s recommendations.

In the ground, cucumbers benefit from a dose of fertilizer a minimum of once a month. Established plants in pots may require a dose weekly or bi-weekly, depending on the strength of the type you choose. 

Verdict: Best Fertilizer for Cucumbers 

So, no it comes down to what to buy. My first place choice goes to Espoma Garden-Tone. This organic, granular fertilizer features its patented Bio-tone microbes to ensure a steady flow of nutrients into the soil so that your cucumber plants grow strong and healthy with zero risk of fertilizer burn.

Next, Dr. Earth’s Organic Tomato, Veg & Herb feed. This fertilizer gives you the option of either digging into the soil or using it as an organic fertilizer tea. It is just what you need to increase phosphorus levels as cucumber plants become more mature.

FAQ’s Fertilizing Cucumbers

If you’re still left wondering and have more questions about growing cucumbers, here’s an insight into what I regularly get asked about this easy to grow and thoroughly rewarding summer edible plants.