Pumpkin MythBusters: Do Bloom Boosters Work?

If you go into any garden center you'll find one or more bags of bloom boosters in the isles.  Any grower who sees those bags at big box stores and garden centers could easily conclude if you want more flowers on your pumpkin plant around pollination time then adding some bloom booster could give you the desired results.  But does it?

Most bloom booster formulas have a higher amount of phosphorous, potassium or both and usually a lower amount of nitrogen.  The amount in each formula tends to differ, which suggests their isn't a consensus on the perfect bloom booster formula.

Pumpkin plants need a certain amount of phosphorous and potassium to grow properly.  The goal of any grower looking to grow big has to be to keep nutrients within the narrow margin for optimal growth.  Too much of most nutrients and you'll have problems.  Have too little and you'll have problems. Get it right in the Goldie Locks zone and you'll grow big all the time.

Phosphorus is critical for plant growth, but plants don’t need a lot of it. The American Rose Society says “Commercial  growers of roses for cut-flower production typically use fertilizers with a 3-1-2 NPK ratio.”  Most soils are not deficient in phosphorous and phosphorous does not leach from soils so typically very little is required.  So adding extra phosphorous to the soil may be creating a less than optimal or even toxic soil if it is overdone. 

One study looking at flowering rate based on nitrogen, phosphorous and potassium application rates found that "the P requirement...is low for reproductive development. Each plant produced over 20 flowers, even when no P was applied."  Suggesting that as long as their is sufficient phosphorous for flowering that adding more will have little to no impact on flowering.

Potassium plays an important role in regulating water and nutrient movement in a plant.  You'll also find high levels of potassium in a pumpkin.  Basically potassium acts like a pump in moving water between cells and with that moving nutrients through the plant.  Unless a plant is very potassium deficient to the extent it is impeding water and nutrient movement, it won't affect flowering.  Potassium, as a result, has little direct effect on flowering.

So what does affect flowering?   Plant hormones.   Auxins (IAA), cytokinin and gibberellin in particular. When the right levels of each hormones are in place than there are signals to the plant to go from vegetative growth to flowering and fruit.  This makes sense right?   When your pumpkin plants main vine gets from 7 to 12 feet out from the stump then suddenly flowers start appearing, right?  It wasn't the addition of potassium or phosphorous that suddenly made the flowers appear.  There is a clear change in the plant that happens around that stage of growth and that change is hormonal and not so much nutrients as long as the minimum required amounts are available to the plant.

So the myth of "bloom boosters" is busted.  If you want more flowering and earlier flowering then you'll need to manipulate the plants hormones and not the nutrients.  Although that probably isn't advisable.  Give the plants what it needs and be a patient grower and you will probably yield bigger pumpkins by the end of the season.