A timely question came into Ask Gardenerd this week from David D.: I am growing Seminole pumpkins in Florida. I have numerous fruit which sometimes get big enough to pollinate and some fall off before the female flower opens. I have had to self pollinate so far. Is it possible there are too many fruit and the plant does that so it can feed the rest. I would like to pollinate as many as I can. Thank you.”
You’re absolutely right, David. Pumpkins and other squashes will abort unpollinated fruits if they don’t have enough nutrients to support growth. It also happens if no male flowers are present when the female flowers open. But that’s not your issue here. Your issue is: FEED ME, SEYMOUR!
Pumpkins are Heavy Feeders
Pumpkins and other winter squashes (and some summer squashes) are considered heavy feeders, meaning they need to grow in rich soil with plenty of nutrients. Since phosphorus and potassium are responsible for flowering and fruiting, make sure your soil has enough to support growth through the season.
Our favorite source of phosphorus is Seabird guano. Our favorite source of potassium is Maxicrop kelp meal. You can mix these individual nutrients into your soil before planting, or top dress as flowers start to appear. But be sure to test your soil for levels before adding. Remember, more is not necessarily better. You can really screw up your soil by over-amending. And watch out for adding too much nitrogen. That can tax plants and put pumpkin babies at risk too.
Balanced organic veggie fertilizers (pre-mixed by companies like Dr. Earth, E.B. Stone, Fox Farm, etc.) will also provide sufficient nutrients for growing crops. If you’re not up for the single-nutrient challenge, just go with pre-mixed brands.
Don’t Forget The Soil Food Web
Many times, soils already contain all the nutrients they need to grow healthy crops, but phosphorus and potassium are often bound up, making it difficult for plants to access them. Healthy soils contain billions of microbes that mine these minerals for plants. Make sure your soil biology (strong populations of beneficial fungi and bacteria) is up to snuff. Use aerated compost tea to boost microbial populations and they will do the work for you.
Stress (hot temperatures, sudden temperature shifts, etc.) can also cause plants to abort their fruit. So can blossom end rot (which is also caused by a nutrient deficiency). Bottom line, check your soil and feed accordingly. Boost your soil food web and that will stop your pumpkin fruits from dropping.
We hope this helps you achieve the Great Pumpkin Patch you desire, David D. Thanks for writing in and Happy gardening!