Pumpkins need a lot of fertility, especially Nitrogen and Potassium, and dislike very acidic soils. So, before you seed your pumpkins, you will need to make sure that the area where you want to plant them has a soil pH in the neighborhood of 6.0 to 6.5. Pumpkins can tolerate a basic pH of around 7.5, so those of you with alkaline soils can rejoice!
You will also want to add compost or aged manure and a good source of potassium such as alfalfa meal or wood ash (use this sparingly because it can lead to soil salinity problems) to your growing area.
If you have a short growing season, and want to grow a relatively long-season variety of pumpkin, consider transplanting your plants. You will have to handle your pumpkin seedlings carefully so that they won't be to set back by the transplanting process: don't allow them to get root bound in their pots, and make sure to keep their root ball intact when you put them into the ground.
Once your plants have germinated and are growing happily, the will flower abundantly. Pumpkins need a lot of pollination in order to set fruit. In fact, a pumpkin flower needs to get eight to twelve visits from a honey bee or other pollinating insect in order to set fruit. Since pumpkin flowers are only fertile for one day, this is a feat that requires an army of pollinating insects to accomplish. Getting adequate pollination is one of biggest challenges that pumpkin growers must overcome.
Fortunately, organic grower's gardens are often havens for bees and other beneficial insects that thrive on the diversity of flowering plants that are available to them in a typical organic garden. More importantly, organic gardeners don't spray long-lasting insecticides that kill pollinators.
Floating row cover, crop rotation and keeping your garden neat and clean are three things that will help keep your pumpkins relatively pest and disease free. Keep in mind that in some areas of the country, such as the humid, buggy, Southeastern US, growing organic pumpkins is an uphill battle!
Covering your young plants with floating row cover and keeping them covered until they flower, will help keep some pests, notably squash bugs, from getting to them before they have a chance to set fruit. Determined growers can even leave the row cover on the pumpkins the whole growing season, as long as they pull it off every morning during the period that the vines are flowering. This will allow the pollinators to get to the flowers while they are open (usually dawn to noon or so) but allow the plants to keep their bug protection during the rest of the day.
Keeping insect pests off of your plants will also help prevent many plant diseases which are transmitted via the pests. Removing diseased or infested plants from your garden promptly (its often better from your pumpkin's point of view to landfill or burn these plants rather than compost them) and keeping the areas around your pumpkin patch mowed will also reduce insect populations and disease pressure.
You're pumpkin patch is likely to make you the talk of your block this Halloween. Now, all you have to do is convince your trick or treaters to eat roasted organic pumpkin seeds instead of Snickers bars. . . On second thought, maybe it would be better to just stick with the candy! Happy Halloween!