Question
I have searched and found no answers as to what kind of fertilizer to use on pumpkins or watermelons. We will be planting in the spring for re-sale. Hope you can tell me what kind we need. Thanks!

Answer
Pumpkins ('Cucurbita pepo') and Watermelons (慍itrullus lanatus? are tender plants that love Summer heat and do not transplant well.  Peat pots solve that problem.  If you are growing your Pumpkin patch and your Watermelons up North around here, you'll need more time than our short growing season allows; you need a minimum of 3 months of serious, warm, Summer weather to grow Pumpkins and Watermelons mature enough to harvest.  Besides, Seeds of these crops don't germinate effectively unless the soil is at least 80 degrees F -- the hotter, the better -- and the Pumpkin and Watermelon vines won't be doing any significant growing unless the weather is in the 80s.  Watermelons need, of course, a lot of Water, much more than Pumpkins.  On the other hand, Pumpkins prefer an acid pH around 5.5 to 6.5.  Both need heat, time and elbow room.  Not to mention all the right vitamins and minerals.

Which brings us to your question.

I am guessing you expect to zero in on a few major minerals to get the best Pumpkins and Watermelons.  Have you gotten your soil tested?  Both will grow best in rich, healthy loam with efficient drainage and moisture when they need it.  Boosting the entire band width of Nitrogen, Potassium and Phosphorus (N-P-K) is essential; zeroing in on a single nutrient is not going to support growth of the whole plant.  Skip the leaves, for instance, and you won't have the leaves using photosynthesis to generate the high levels of energy needed to build a Pumpkin crop.  

You've got to feed the whole Pumpkin plant, the entire Watermelon vine, to get good vegetables, whether you're shooting for quantity or Giant quality.

Bone Meal, Fish Emulsion, Leaf Mould -- and a minimum of concentrated fertilizer (this means those flashy, Madison Avenue-promoted Miracle Gro products) -- will sustain the best possible growth for your Pumpkins and Watermelons.  Get your Soil tested so you know what you抮e missing and what you have plenty of, then correct it.

What's wrong with concentrated fertilizer for your vegetables?

Well, if you are growing your crop(s) in poor, depleted Soil, I guess you are stuck with the narrow band width and balancing act.  But you'll never be able to copy the slow, steady, temperature-driven output of rich Soil that builds superb taste and quality.  Never.  Not even slow release fertilizer can do it Nature's way.

If you don't mind compromising on quality and quantity, however, or if you need more control to feel comfortable, you can probably get satisfactory results by using one of the balanced fertilizers that you mix with water.  The biggest feeders are the Giant varieties.  Pumpkins typically need apx 2 lbs N, 3 lbs P and 6 lbs K for every thousand sq ft of Soil; Watermelons, in contrast, respond as many plants do to excess N, producing leaves at the expense of fruit.  A shortage of Calcium can lead to Blossom-end rot. But the solution is not necessarily to add Calcium; low pH or faulty watering can cause the same problem.  

Your Soil test will determine how much IF ANY fertilizer you will need to feed it.  To get the most out of the concentrates, dilute heavily and use every time you water, instead of the recommended once a week or twice a month.  Increase the dosage and frequency as temps heat up; slow down feedings when a cold front moves in.  And next year, practice crop rotation so you don抰 deplete every trace of minerals in the Soil.

Megaton Watermelons and Pumpkins are goals achieved less with fertilizer, more with a knowledge of growing techniques.  Select Jumbo-size seed varieties, and provide a long, hot growing season.

When the vines start to bloom, pull off the first 3 female flowers; vines will grow bigger, with more leaves, before they set fruit.  Initial flowers on Watermelons and Pumpkins and similar crops often fail to produce fruit, so odds are you are not diminishing production by getting rid of these flowers.

Depending on how badly you want to grow super-sized vegetables, tiny doses of Gibberellic Acid or another growth hormone used by mad bioscientists will stretch cells and ultimately grow Giant Pumpkins and Watermelons.  The growth does have to be supported by super-rich Soil, and you do have to know what you抮e doing -- too much or too little GA, and the experiment fails.

The Ohio State Extension Service posts a page on growing the ultimate Pumpkin:

http://ohioline.osu.edu/hyg-fact/1000/1646.html

University of Illinois Cooperative Extension posts a Pumpkin Page:

http://www.urbanext.uiuc.edu/pumpkins/growing.html

For size, there抯 the 慦orld Class Giant Pumpkin?website, mainly links for advice posted by Pumpkin specialists:

http://www.backyardgardener.com/wcgp/index.html

My favorite advice is the ?0 Steps to a Big Pumpkin?or something like that:

http://www.backyardgardener.com/wcgp/tips/10steps/10steps.html

University of Georgia抯 College of Agriculture publishes a page with extensive instructions about Watermelon growing:

http://pubs.caes.uga.edu/caespubs/pubcd/B996-w.htm

Good luck, and please do keep me posted.