- The soil food web. Organic fertilizers feed what is called the soil food web. Chemical fertilizers can diminish the soil food web. The soil food web is the community of bacteria, fungi, protozoa, dirt, plants, and organic material in the soil working together synergistically to feed and help each other. You see the best of this in jungles and forests where the plants thrive without much outside intervention. Organic fertilizers typically build this community and add to it. Chemical fertilizers can diminish some communities in the food web and this breaks the natural cycles. So what you end up doing is feeding the plant rather than the soil.
- Salts. Most chemical fertilizers when they break down leave salts behind. These salts will build up over years of fertilization and could hurt your pumpkin plant some.
- Micro nutrients and hormones. Some organic fertilizers contain micro nutrients and plant hormones that most chemical fertilizers do not have. A good seaweed fertilizer contains growth promoting substances like auxims, cytokinins and gibberellins that can increase the size of your plant and in turn your pumpkin.
Some people go a little psycho in regards to the whole organic verses chemical fertilizer debate. The reasons above is why I only use organic fertilizers. They can be a slightly more expensive, but I think they are worth it to add a few more pounds to the pumpkin.