8 Best Fertilizers For Pumpkins, Squash And Watermelons | How And When To Use

Biting into a juicy piece of melon tastes like summer holidays and picnics. While ripening pumpkins and squash on the vine harkens the arrival of cooler autumn days and harvest time.

Squash and melons may be completely different plants but there’s one thing they have in common. They all need a healthy dose of nutrients throughout the season. Which is vital to flower production and ultimately, delectable melons and squash. Since no two gardens are alike, I’ve gathered for you a comprehensive list of the 8 best fertilizers for pumpkins, squash, and watermelons. Each one brings something unique but all are greatly effective for producing a large and tasty bounty.

Choosing Fertilizer For Pumpkins, Squash And Watermelons

The interesting thing I’ve discovered on the path to growing large and nutritious squash and melons is that they need higher doses of different macronutrients throughout the growing season. 

For example, pumpkins and squash need more nitrogen, early on, to form strong roots, leaves, vines, and flowers. Once flowers appear, these plants need more phosphorus to generate an abundance of blooms. Then, when those flowers evolve into pumpkins and other types of squash, they require more potassium to form large, healthy fruit.

Watermelons are similar in that they also need a nitrogen-focused feed, at first. Then, once flowering occurs, they’ll need an equal amount of phosphorus and potassium for perfectly formed and juicy fruit. This is definitely something you’ll want to keep in mind when choosing the best feed for your crops.

Fertilizer Ratio N-P-K

Now that we know what specific nutrients are required at different stages, where do we go to find those? The best fertilizer for pumpkins, squash, and melons will have a higher proportion of these different macronutrients reflected in their NPK.

PRO-TIP: The NPK of every fertilizer is displayed as three numbers on the label. These numbers are the N-P-K ratio of that fertilizer, indicating its proportions of nitrogen, phosphorus, and potassium. For example: A 24-8-16 NPK contains 24% nitrogen, 8% phosphorus and 16% potassium. 

Pumpkins Fertilizer Ratio

As a start, a 10-5-5 NPK will strongly support root formation and growth. As flowers begin to form, switching to a 5-10-10 NPK and supplementing with a bit of bone meal or rock phosphate will encourage an abundance of blooms. Finally, once pumpkins appear, eliminate the extra phosphorus and allow the potassium to boost pumpkin size and formation.

Squash Fertilizer Ratio

Since pumpkins are a type of squash, the above recommendations can also be applied to these. However, many squash varieties don’t grow as large. So, an equal balance of phosphorus and potassium, once flowers appear, would work just fine. As you’ll find in some of the options in the below list.

Watermelon Fertilizer Ratio

As mentioned, melons have similar needs to smaller squash varieties. In that, they prefer more nitrogen in the beginning. So, they would greatly appreciate a 10-5-5 NPK at this point. Once flowering, melons also do well with an equal balance of phosphorus and potassium. Although, if you’re in the practice of adding compost to your soil, you could get away with using an equally balanced NPK like 10-10-10 for fruits and veggies.

Granular Vs Liquid Fertilizer

Liquids can save water and time, especially if you choose one versatile enough to use when watering the rest of your fruits and vegetables. Nutrients are carried to the root system through the soil right away, allowing for immediate uptake. This method is especially beneficial for those living in northern regions with shorter growing seasons. Liquid feeds also tend to keep the pH levels in your soil balanced. However, caution is recommended, as over-feeding could lead to root burn.

Granules are a slow-release choice. Heavily concentrated, they provide consistent nourishment for several months at a time. No watering is needed to activate in areas with substantial rainfall and is less likely to leach into nearby surface or groundwater.

Organic Vs Synthetic

Choosing an organic or synthetic fertilizer is simply a matter of preference and end-result expectations. A basic understanding of the difference can help you make a solid fertilizer choice for your crops.

Organics are typically plant or animal-based using manures and composted materials. Inorganics are mass-produced using minerals and synthetic chemicals. Organic feeds generally contain lower levels of nutrients but can nourish your squash and melons for longer periods of time. This option can also improve the surrounding soil. The use of inorganic feeds can result in larger fruits and vegetables as well as a higher yield. But, they can also potentially contaminate nearby water sources.


8 Best Fertilizers For Pumpkins, Squash & Watermelon

After careful research, personal experience, and delving into the experiences and feedback of peers and other home-growers on many of the best gardening forums and retail sites, I present my list of picks for the 8 best fertilizers for pumpkins, squash, and watermelons.


1. Plant Magic All Purpose Organic Fertilizer 6-5-5

Plant Magic All Purpose Organic Fertilizer

First up, for new plantings at the beginning of the season is this nitrogen-focused, organic fertilizer from Plant Magic. This all-natural, soluble powder has an NPK of 6-5-5 and also contains more than 55 trace minerals.

It also contains all the microorganisms your soil could possibly require to perform as well as natural compost. Quite an impressive boast but one I had to try out for myself. Let me tell you, I am certainly glad I gave it a shot because my squash and melon seedlings took off like bullets.

My young plants not only looked healthy and vibrant in color, but they were also easily strong enough to be able to support the weight of the fruit as it grew. And, my crop was impressive in size too. All this while being non-toxic and safe for my family and all of our animal babies. This is definitely a product I’ll return to each year. It’s a big hit with me. Click here to buy Plant Magic All Purpose Organic Fertilizer here.

Check Plant Magic’s latest price on Amazon

How To Use: This can be applied (as directed on the label) as a slow-release additive directly into the soil or diluted with water for immediate absorption.  I added it directly to the top layer of soil because I’m confident that my compost is already nutrient-rich but you can also mix it with water during normal watering if you want an instant hit of goodness.

Customer Reviews: Master gardeners and first-time home-growers alike are reporting how pleased they are with getting the same organic results from this product as they would from adding handmade compost. And the versatility of the application makes it easy to use no matter which method you prefer. Awarding this pick 4.5 / stars and our choice for BEST BUY.

Pros      

  • Same results seen as with handmade compost
  • Improves soil while being safe and non-toxic

Cons

  • May exhibit an organic odor when applied

2. Miracle-Gro Performance Organics Granules 7-6-9

Miracle-Gro Performance Organics Granules

This second organic option from Miracle-Gro is one of my top picks based on ease-of-use and price vs results. It has been approved for use on fruits and vegetables, has a 7-6-9 NPK, and the promise of a bountiful harvest and results in just 7 days compared with unfed crops.

Well-known for its dependability, Miracle-Gro’s new organic formula gave me the type of crop yield you might expect if you were to use an inorganic fertilizer. Thankfully, this granular formula comes with peace of mind that I’m feeding my edible plants something natural and also an endorsement by the Organic Materials Review Institute. Definitely, a “must try”. Check prices of Miracle-Gro Performance Organics Granules here.

How To Use: The flip lid dispenser makes applying the granules easy and mess-free. Simply shake and pout around the base of your established plants. You will need to measure out your plot beforehand to make sure that you are not overfertilizing. Water as normal and repeat every 4-6 weeks throughout the growing season.

Customer Reviews: Home-growers are reporting filling their freezers with the abundance of crops yielded from this product. Tasty and juicy fruits and veggies give Performance Organics a 4.6 / 5 stars.

Pros      

  • Vigorous growth and plant vitality with consistent use
  • Increased yield with a balanced NPK

Cons

  • Not recommended for use as a water soluble fertilizer

3. Miracle-Gro Organics All Purpose 11-3-8

Miracle-Gro Organics All Purpose

If you prefer a quick-release liquid option, then Miracle-Gro offers a water-soluble formula with their Performance Organics range. This fertilizer for pumpkins and many other fruiting plants have more nitrogen than the granular formula above, with an 11-3-8 NPK, but has all the essential micronutrients to provide the same high-yielding results. The formula just gets to work and delivers results in less time. 

I used a hose attachment to administer the fertilizer across my crops, but a watering can is just as effective. The end result is the same as with the granule option. Strong, healthy, and vibrant plants and crops that look well-nourished, right from the first planting, through to harvest. Click here for Miracle-Gro Performance Organics All Purpose Water Soluble.

How To Use: I added two level scoops and set the gauge on my hose attachment to one gallon of water. This one is gentle enough to be applied once per week throughout the growing season.

Customer Reviews: I noticed across many forums how gardeners who are long-time users of Miracle-Gro’s flagship vegetable feed were at first hesitant to switch to an organic option. That was until they saw the same, dependable results they had come to expect. Reporting they’ll stick to organic now, going forward. Earning this quick-release option 4.6 / 5 stars.

Pros      

  • Quick-release for immediate nutrient absorption
  • Helps to improve nutrient-poor soil

Cons

  • May exhibit a slight organic odor

4. Lilly Miller All Purpose Food 10-10-10

Lilly Miller All Purpose Food

This 10-10-10 NPK from Lilly Miller provides the right amount of phosphorus and potassium support for large and nutritious fruit production. This is a great product to use if you are concerned about the size of your pumpkins, squash, or melons as they begin to emerge after flowering.

It is an organic fertilizer and is versatile enough to use throughout your garden on flowers, as well as all other edibles. This is a granular option that is best used in the second stage of fruit development and provides the option as either a slow-release feed or by mixing with water and adding it to your watering can for immediate action.

How To Use: Either work into the soil or dilute the recommended amount in water. Then, apply every 4-6 weeks after flowering. Click here to check Lilly Miller prices at Amazon.com

Customer Reviews: Gardeners are reporting great success with this product after years of trying to grow crops in poor soil. A higher yield of juicier and healthier fruits plus the versatility of application awards Lilly Miller’s vegetable feed an impressive 4.7 / 5 stars.

Pros      

  • Can be used as a slow or quick release application
  • Higher yield of healthy crops grown in poor soil

Cons

  • May not contain enough nitrogen for early stages of plant development

5. JR Peters Jack’s Classic Tomato Feed 12-15-30

Best Fertilizers For Pumpkins

Another water-soluble, potassium-rich option comes from Jack’s. I have been an advocate of their classic 12-15-30 NPK fertilizer and have used it on my vined fruits – particularly tomatoes and squash for the last 3 years.

This particular blend of micro-nutrients gets to work straight away as it is absorbed by roots and foliar to encourage green, voluminous, and lush foliage as crops develop. All of this means goodbye to leggy or spindly growth and hello healthy, bountiful harvest.

How To Use: This one comes with a measuring spoon and you just need to mix 1 spoonful with one gallon of water. Then apply over the entire plant. It can be easily combined with regular watering as you need to repeat every 7-10 days to make sure you are providing a consistent flow of nutrients.

Find Jack’s Classic Tomato on Amazon.com

Customer Reviews: Jack’s Classic has become an absolute must for gardeners in areas with a short growing season. The quick-release application means faster absorption and vigorous growth, just in time for early harvest. 4.8 / 5 stars.

Pros      

  • Water-soluble for immediate nutrients intake
  • Potassium-focused to large, healthy fruit formation

Cons

  • Over-applying may result in leaf and root burn

6. Osmocote Smart-Release Plant Food Flower & Vegetable 14-14-14

Osmocote Smart-Release Plant Food Flower & Vegetable

This granular option from Osmocote is specially formulated to release beneficial nutrients for up to 4 months at a time. This 14-14-14 NPK choice allows me to provide slow-release, nourishing support for not only my veggie patch but all of my flowering plants and can be used from the first planting, right up until harvest.

The gentle formula means it is even suitable for use on nutrient-rich, well-composted soil too. Good news if you crave more free time to enjoy other warm-weather activities knowing your garden is good to go.

Check Osmocote Smart-Release latest price here

How To Use: Work 3 tablespoons, per 4 square feet, into the top 1-3” of soil and water regularly. Repeat every 4 months.

Customer Reviews: Everyone from horticulturists and biologists to home gardeners struggling to successfully winter over their perennials are reporting they won’t use anything else but Osmocote. The ease of use for both crops and garden flowers gives this product very good value for money. 4.7 / 5 stars.

Pros      

  • Well-balanced NPK for crops grown in nutrient rich soil
  • Slow-release of nutrients for up to 4 months

Cons

  • Tiny pellets may be left behind once feed has dissolved into soil

7. Dr. Earth Organic & Natural All Purpose Fertilizer 4-4-4

Dr. Earth Organic & Natural All Purpose Fertilizer

Another safe feed for well-composted crops is this well-balanced, non-toxic option from Dr. Earth. In my experience, the 4-4-4 NPK can’t be beaten for gentle nourishment, without the risk of overfeeding. And, it continues to provide nutrients for up to two months.

Find Dr. Earth latest price on Amazon.com

How To Use: In veg beds, work 1 ⅓ cups for every 10 sq ft of soil. In containers, work in 2 tablespoons for every 4 liters (1 gallon) of soil. Repeat every two months.

Customer Reviews: Gardeners are happily reporting that this product is even gentle enough to add to compost teas for an extra boost. Resulting in higher-than-expected crop yields and plentiful blooms on flowering annuals and perennials. 4.7 / 5 stars.

Pros      

  • Gentle enough for use with natural composts
  • Safe for people and pets

Cons

  • May not be appropriate for plants growing in nutrient-poor soil

8. Joyful Dirt All Purpose Organic Plant Food and Fertilizer 9-1-5

Joyful Dirt | All Purpose Organic Plant Food And Fertilizer

Are you a gardener who lives in a region with a short growing season? Then, my last pick may be the one for you. Because of our long winters, I have to start certain crops inside while there’s still snow on the ground outside.

Using this as slow-release fertilizer in early spring allows me to put already vigorously growing plants and crops outside as the weather warms up. Giving them plenty of time to develop toward a high-volume, healthy harvest. Find Joyful Dirt online here

How To Use: Either work in 1/8th of a teaspoon evenly over the soil. Or, mix 1 tbsp into 1 gallon of water. Then, water normally. Repeat once a month.

Customer Reviews: Avid gardeners who adore houseplants and like to start their garden seeds indoors in early spring swear by this option from Joyful Dirt. When used as directed, flowering and non-flowering plants alike really respond well. 4.5 / 5 stars.

Pros      

  • Get winter-dormant plants off to a great spring start
  • Versatile enough for use on houseplants as well

Cons

  • May not be appropriate for plants growing in nitrogen-rich soil

Fertilizing Pumpkins and Squash

So, as we’ve seen, there are quite a few great options out there to suit the specific needs of your pumpkins and squash. Let’s recap what they need and when for a bountiful, delicious harvest.

How To Fertilize Pumpkins & Squash

Young plants need a hardy dose of nitrogen to form robust root systems that will then produce the strong vines and stems needed to support large squash. Once flowering, a switch to phosphorus and then potassium will result in large, nutritious pumpkins and squash.

When To Fertilize Pumpkins & Squash

Applying fertilizer is beneficial throughout the growing season but the frequency and amount may vary depending on the type of squash you’re growing. For example…

Winter & Summer Squash

Winter squash varieties tend to be heavier feeders than the summer assortment. How often to feed each of these will depend on the fertilizer type and application method you choose.

Giant Pumpkins

For giant “show” pumpkins, fertilization begins when the seed is planted. Around the beginning of May. Upon germinating, the 2nd dose is applied. At the beginning of June, a 3rd dose is applied and repeated every 14 days until harvest.

Fertilizing Watermelons

As with squash, feeding watermelon plants is most beneficial when consistently applied throughout the growing season.

How To Fertilize Watermelons

An NPK with a higher amount of nitrogen should be applied at the time of planting until they flower. Then, switch to one with higher but equal amounts of phosphorus and potassium, until harvest.

When To Fertilize Watermelons

Your watermelon feeding schedule should coincide with the growing stages of your plants. These will vary according to climate, growing conditions, and the type of feed you choose.

Final Thoughts

With a bit of careful planning, growing pumpkins, squash, and watermelons will not only add joy to your summer gardening activities but also to your holiday picnic table as well. Adding to your scrapbook of wonderful, seasonal memories.

With so many fruitful options on this list of best fertilizers for pumpkins, you’re bound to find the perfect feed to suit your climate, soil conditions, and activity level. Will it be Plant Magic’s all-natural feed that is loaded to the roof with macro and micronutrients and trace element minerals? Or, will it be one of the Miracle-Gro organic formulas? Miracle-Gro Performance Organics Granules or Miracle-Gro Performance Organics Water-Soluble. Both of which will bring you healthy crops and a bountiful harvest but do you prefer slow-release granules or a fast-acting liquid formula?

No matter which, I hope that my carefully researched list has provided you with some helpful information and access to success.