Fertilising your Giant Pumpkin

Think of fertilising your giant pumpkin plant as feeding it the nutrients that it needs to grow the best it can. If you want the biggest best giant pumpkin around, one that will win competitions you will want to have your fertiliser plan working well.

What is Fertiliser?

Fertiliser is a substance used to promote plant growth by providing essential nutrients. It is typically added to soil or directly to plants to balance nutrient deficiencies and enhance their health and productivity.

Fertilisers contain a combination of elements like nitrogen, phosphorus, and potassium, as well as trace elements such as iron, zinc, and manganese, which are crucial for plant development. They come in various forms including granules, powders, and liquids.

What is a complete or incomplete fertiliser?

You may hear these terms mentioned when looking at fertilisers.

Simply put a complete fertiliser has all three nutrients present and could look like 5-10-5 for the NPK percentages on the label.

An incomplete fertiliser is one that is missing one of the major nutrients. The NPK label could look like 0-0-40

Have you done soil tests?

Fertilising without a soil test can lead to the wrong products being applied to a plant that may be needing something else.

But soil test aren’t for everyone. While common place and cheap in the US. Soil tests here in New Zealand aren’t giant pumpkin focused and expensive.

If you want to go down that path you really need to commit to the cost of the test, and then the cost of the products you need to get to amend your pumpkin patch.

Get your soil test interpreted 

If you have got a soil test done, it should show you a range that your nutrients are in. Some may be too low, others too high and if your lucky a whole bunch should be in the optimal range.

Talk to someone that knows how to read these. They can offer you advice on the best products, what can effect other nutrients or what might lower one and raise another. Reach out to one of the pumpkin growing groups on Facebook, or head over to BigPumpkins.com and ask on the message board. 

Here’s a couple of things that could help you with your soil test results.

Guide to Interpreting Soil Test and Managing Fertility

The St. Croix Growers Association has a guide to help you with soil tests. This is what they say about it:

Growing a giant pumpkin requires good luck, good weather, good seed, and good soil. Of those four, soil is the factor we have the most control over. This ten-page booklet recommends labs to work with, which lab test profiles to run, how to collect a soil sample, and interpretation and management suggestions for pH, CEC, calcium, magnesium, potassium, nitrogen, sulfur, organic matter, phosphorus, & the micronutrients. The only guide of its kind that provides specific fertilizer suggestions based on your soil test results and patch size.

I have not used this guide, so can’t vouch for it at all. But for only $12 it seems like a good deal.

Check it out by going here:

Bryan Langley’s Soil Estimator

Bryan Langley's soil estimator spreadsheet to help balance the nutrients when fertilising a giant pumpkin patch

If you are wanting to get more in depth with your soil test results you can check out this soil estimator.

Bryan has made a great excel spreadsheet that helps you figure out what you could do with your soil to make it better.

The Illinois Giant Pumpkin Growers Association has a link for you to download it.

To help you understand it and how it works. Make sure to check out this great companion video created by Cecil.


  • Big thanks to Bryan and Cecil for these great pieces of information
  • The fertilisers already loaded into the spreadsheet might not work for your location, as you may not be able to get them in your part of the world

No soil test?

If you aren’t in a position to get a soil test done. Don’t worry. There are basic principles you can follow to help your pumpkin grow. Which will be better than doing nothing and can help you reach the next step in your giant pumpkin growing journey.

You’ll also want to look at different signs of nutrient deficiencies in your plant by looking at the color or the leaves and how the plant is growing. I have more information around this on the diseases page.

What type of fertilisers could you use?

There’s two ways fertilisers can be made. Some people can have strong opinions about this. 

  • Man made chemical fertilisers
  • Organic fertilisers made from natural materials

I don’t think there is any right or wrong answer when it comes to the types of fertilisers myself. You might even use a mixture of both, depending on what your plant may require. Cost might also play a part on your decision making process when it comes to what you use.

Keep in mind that a lot of products mentioned overseas aren’t available here in NZ. Trying to find products that have levels like those found overseas can sometimes be hard.

How plants use these nutrients

Here’s a video I found that explains the different ways nutrients work in plants. It’s a super basic video to give you a primer on nutrients.

For a more detailed video that is more focused on giant pumpkins, watch this video created by Cecil.

Nutrients Giant Pumpkins Use to Grow

Here’s the main nutrients giant pumpkin plants and most plants use to grow. These are the ones you are likely to see on a soil test report.

There’s a couple of others mentioned when you look up plant nutrients, but are required in small amounts and not mentioned much when talking about giant pumpkins. I’ve left those ones out.

Nutrients needed for plant growth chart, including giant pumpkins

The Big 3 Macronutrients

No matter what you are growing. Plants require different amounts of nutrients at different parts of their growing cycle.

The main nutrients which you will see listed on packaging are NPK

Nitrogen, Phosphorous and Potassium

Nitrogen (N)

Nitrogen is crucial for the growth and development of plants, including giant pumpkins and their vines. It is an essential component of proteins, enzymes, and chlorophyll, which are vital for plant metabolism and photosynthesis. Nitrogen is primarily responsible for promoting vegetative growth in plants, helping them develop strong stems, lush leaves, and robust root systems.

In the case of giant pumpkins and their vines, adequate nitrogen levels are particularly important as they require substantial amounts of nutrients to support their extensive growth. Furthermore, nitrogen deficiency can lead to stunted growth, yellowing of leaves, and reduced fruit production.

Too much nitrogen can also reduce or delay the amount of flowers that are present, if this seems to be the case just stop adding the fertiliser for a week or two.

Phosphorous (P)

As one of the essential macronutrients, phosphorus is necessary for energy transfer, DNA replication, and cell division processes in plants. It aids in promoting root development and overall plant structure, making it particularly vital during early growth stages.

Phosphorus also aids in the transportation of other nutrients within the plant, ensuring proper nutrient uptake and utilization. Insufficient phosphorus levels can lead to stunted growth, reduced yield, and poor fruit development. 

Potassium (K)

Potassium plays a vital role in plant growth, particularly for giant pumpkins and pumpkin vines. It is one of the essential macronutrients required for overall plant health and development. Potassium helps in the formation of carbohydrates and proteins, aiding in the growth and reproduction processes of plants.

Additionally, it regulates water uptake and nutrient transportation within the plant cells. Potassium also strengthens the cell walls, making plants more resistant to diseases and pests.

It enhances photosynthesis, enabling plants to convert sunlight into energy more efficiently. In the case of giant pumpkins and pumpkin vines, potassium helps in fruit development, resulting in larger and healthier pumpkins. Maintaining adequate potassium levels through proper fertilization is crucial for robust growth and high-quality yields in these plants. 

Other Macronutrients

These are sometimes referred to as secondary or tertiary macronutrients. 

Calcium (Ca)

Calcium plays a crucial role in plant growth as it aids in cell wall development, enzyme activity, and nutrient absorption. It helps to strengthen the cell walls, giving the plant structure and stability. Calcium also acts as a messenger within the plant, signaling growth processes and regulating various physiological reactions.

Additionally, calcium assists in the transportation and uptake of other essential nutrients, helping plants to thrive and develop properly. 

Magnesium (Mg)

Magnesium is an essential nutrient for the growth and development of plants. It is a key component of chlorophyll, which is responsible for photosynthesis, the process through which plants convert sunlight into energy.

Magnesium also plays a crucial role in enzyme activity and the synthesis of nucleic acids and proteins. Without sufficient magnesium, plants may experience stunted growth, yellowing leaves, and reduced overall productivity.

Sulfur (S)

It plays a crucial role in various enzymatic and metabolic processes. Sulfur is especially important for the synthesis of proteins, which are essential for plant growth and development.

It also helps in the formation of chlorophyll, the pigment responsible for photosynthesis. Sulfur enhances root development, promotes better nutrient uptake, and improves overall plant health.  


You can often see these also referred to as trace minerals. These are required in much smaller quantities by plants, but are still important for good plant health.

Iron (Fe)

It is required for various essential processes, such as chlorophyll production and the synthesis of enzymes involved in respiration and photosynthesis. Iron also aids in the transportation of electrons and acts as a catalyst for important metabolic reactions, ultimately contributing to overall plant development and productivity. 

Boron (B)

Boron is an essential micronutrient for plants as it plays a crucial role in cell wall formation, carbohydrate metabolism, and proper nutrient uptake. It aids in root development, flowering, pollination, and fruit development.

Adequate boron levels result in healthier plants with improved resistance to diseases and pests as well as increased crop yields. Insufficient boron can lead to stunted growth, reduced seed and fruit production, and various physiological disorders in plants.

Copper (Cu)

Copper is a micronutrient that plays a vital role in plant growth. It helps in the formation of chlorophyll, which is responsible for photosynthesis in plants. Copper is also involved in enzyme activity, assisting in a variety of metabolic processes. Additionally, copper aids in the development and maintenance of plant cell walls, promoting overall plant health and growth.

Manganese (Mn)

Manganese is an essential micronutrient for plants as it plays a crucial role in the photosynthesis process. It assists in the production of chlorophyll, which is responsible for capturing sunlight and converting it into energy.

Manganese also aids in enzyme activation involved in the metabolism of nitrogen and carbohydrates, promoting healthy plant growth and development.

Molybdenum (Mo)

Molybdenum is an essential micronutrient for plants as it plays a crucial role in various enzymatic reactions. It helps in the conversion of nitrate into amino acids, which are essential building blocks for plant growth and development. Molybdenum also aids in the fixation of atmospheric nitrogen by bacteria, ensuring an adequate supply of this vital nutrient for plant growth.

Chlorine (Cl)

Chlorine is an essential micronutrient for plants as it aids in photosynthesis and helps control water movement within cells. It is involved in the production of enzymes and proteins, helps plants resist disease, and promotes root development.

However, excess chlorine can have toxic effects on plants, so it is important to maintain a balanced amount for optimal growth.

Zinc (Zn)

Zinc is a micronutrient that plays a vital role in plant growth and development. It is involved in enzyme activation and stimulates root development, leading to enhanced nutrient uptake. Zinc also aids in the production of chlorophyll and helps in seed formation, ultimately promoting overall plant growth and productivity.

Nickel (Ni)

Nickel is a micronutrient essential for plant growth as it plays a crucial role in several plant enzymes. It is involved in nitrogen metabolism, helping in the conversion of urea to ammonia, a critical step in plant nutrition. Nickel also aids in the absorption and utilization of iron, which is vital for chlorophyll production and overall plant health. Overall, nickel is necessary for optimal growth and development in plants.

Sodium (Na)

Sodium plays a vital role as a plant nutrient, even though it’s not considered essential for all plant species. It serves as a functional substitute for potassium in certain plant physiology aspects. Sodium aids in metabolic processes, stimulates plant growth, and can improve resistance to diseases. However, excessive sodium can be harmful, causing salt stress in plants.

Provide what the plant wants and needs, and slow and steady

The trick to any fertiliser is to provide the plant with what it needs, this can be worked out from just understanding your plants to getting foliar tests done.  Slow and steady is also a key, not overdoing it and causing to much stress on the plant is what you are aiming for here.

You may want to use a lot of product to get great results. The exact opposite might happen. Toxicity from too much of a nutrient could occur. Or you might just be wasting your money.

Make sure to follow either:

  • The recommended application rates
  • Advice from seasoned giant pumpkin growers
  • Working out what your plants are lacking in

With all three of these combined and the correct rates applied you will be well on your way to growing a giant.

How to read a fertilizer bag

On fertiliser bags you will have the NPK listed. This tells you the percentage of these 3 major nutrients in this package per the package weight.

In my example here the NPK is 0-0-41 which tells me that 41% of the bag is made up of potassium. That works out to be 1.025kg of the 2.5kg bag I have.

Front of a bag of fertiliser showing the NPK amounts

A giant pumpkin plants fertiliser needs

If you’ve had a soil test done, you should be working towards amending the soil to be in the best condition it can be for your plant.

But if you aren’t doing a soil test here’s a couple of things that can help you.

The plant needs N P and K in that order of it’s growth.

Nitrogen helps with leaf, root and vine growth.

Phosphorous helps with healthy root growth, fruit setting and development.

Potassium helps with fruit growth.

If you are on a limited budget, pick a well rounded product and follow it’s instructions. I would also supplement with a seaweed type product as well.

Application of Fertilisers

Important point to note is check the application rates. Only apply what you need for your patch size.

Broadcasting – This is where the fertiliser is applied evenly over the soil surface. This could be done for both liquid and dry types of fertilisers.

Fertigation – This method is when the fertilisers are injected into the irrigation system. This could be used with sprinklers or drip tape.

Foliar – Liquid fertilisers are sprayed onto the leaves of the plant. This can be used as a quick way to help with deficiencies during the growing season.

These are the main ways of applying fertiliser for giant pumpkin growing. There are a couple of other methods out there used on other crops.

Growing simply or just getting started

If you are new to this and it all sounds a bit too much. Here’s my suggestion. Get a water soluble fish and seaweed fertiliser. Due to our location and coastlines we have a lot of these products out there.

Follow the instructions and apply to the plant. This type of product will help provide a balanced amount of nutrients to your plan

The main thing to remember when fertilising is that slow and steady wins the race. When you feel the urge to fertilize, remember this, and don’t go overboard.

In conclusion

Fertiliser as you can see is a large topic when it comes to growing giant pumpkins. It’s one part of a puzzle to growing the biggest giant pumpkin you can.

If you can get your soil in the best condition possible and provide your plant with the nutrients it requires at different stages of growth, while giving it enough water. You will be giving your giant pumpkin plant the best chance at success.

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