As discussed previously your pumpkins will thrive in your mixture of manure and compost. As the season progresses and your pumpkins grow bigger, the plants will need more nutrients to produce even bigger pumpkins. Nutrients must be applied on a regular basis right through the season to prohibit slowing or stagnation of growth.
Commercial fertilizers, whether it's granules or in liquid form, contains all the correct nutrients that your plants need and is easy to apply. When you use commercial fertilizers always follow the manufacturers instructions carefully. The golden rule to fertilizing is rather less than to much. To much fertilizers can burn your plants and results in a delay of the flowering stage and even worse can kill your plants. If you're an inexperienced grower, keep to a balanced fertilizer like the 3-2-3 and as you gain experience you can use other fertilizers and even make up your own mixture.
The three most important ingredients for plant growth is normally displayed on fertilizer packages and looks like 3-2-3 (24).
This represents the percentage of Nitrogen, Phosphorous and Potassium in the fertilizer. The (24) stands for the percentage of the three major ingredients to the total volume of the fertilizer. In simple terms if you need a fertilizer with less Phosphorous but more Potassium, the equation will look something like 3-1-5 (22). The order of the chemicals will always be the same : Nitrogen-Phosphorous-Potassium.
Now let's see what each of these elements do for your plant.
NITROGEN improves root, leaf and vine growth. In the early stages apply a fertilizer with a higher nitrogen ingredient like the 3-2-1.
PHOSPHOROUS helps with the flowering and the fruit set. Apply something like 2-3-2 when the plant is about to start flowering.
POTASSIUM promotes fruit growth. Apply 3-1-5 or 3-1-6 just after the flowers died and the small pumpkins starts to grow bigger. Can be applied till it's time to harvest.
Granules are sprinkled around the stem of the plant but not to close to burn the stem. It's a slow release fertilizer and every time you water the plant, a small amount of nutrients are conveyed with the water to the roots.
Liquid fertilizer can be added to the water in the irrigation system in order to reach the roots. It is also used as foliar feeding and is applied with a hand sprayer to the leaves and the vines.
A few rules to remember when fertilizing: Never apply fertilizer to dry soil, first water the plants thoroughly. New plants must not be fertilized in the first 3 weeks. It's better to fertilize on a day when it's not very hot. Always read the instructions before any fertilizer is applied.
... next: Flowers and Polination