Thursday, June 6, 2013

Hand Pollinating Squash

Even with the many other websites that overview hand pollinating squash, I figure that it cannot hurt to review the process. Just like melons, squash are monoecious: meaning that they have separate male and female flowers that grow from the same vine. In order for fruit to mature, this type of plant requires a pollinator to remove pollen from the anther of the male flower and deposit it on the stigma of the female flower.

Immature Male Squash Blossom

Female flowers are identified by the bulbous protrusion on the stem right below the flower, whereas male flowers consist of a thin stalk leading up to the flower.

Depending upon the type of squash you are growing, female flowers may take a while to appear. The 90 days that I waited for my Long of Naples to produce female flowers was nearly enough to persuade me to cut the whole plant down.

Immature female Squash Blossom

Other reasons why female flowers may not grow include a lack of some nutrient. On one occasion, when I had a large zucchini plant with no female flowers, the plant quickly began to produce flowers after an application of a little bone meal. However, the correlation could be considered questionable. Whether the production of female flowers was because of the bone meal or whether the plant would have produced female flowers anyway was difficult to determine.

Mature Female Squash Blossom (side view)

Mature Female Squash Blossom (front view)

Pollinating of squash can occur as soon as a female squash blossom has been identified and that blossom begins to open its large flower. To pollinate, I identify a blossoming male flower, pull it by its stem, remove its large petals and rub the pollen from the male anther gently around stigma of the female flower. As there are usually more male flowers than female flowers, I usually use repeat the process several times using multiple male flowers.

Mature male squash blossom (Tucson ants will even eat pollen!)

Pollinating the female stigma with the male anther

So – how do you know when you’ve pollinated your squash correctly? Within a week the squash should either begin to grow or shrivel up. If it grows, then all the conditions were right for pollination and fruit set.

Squash set fruit - this is usually a good thing

If the fruit does not set and shrivels, this may not be the gardener’s fault. If I have multiple fruits setting at the same time on the same vine, the vine will often abort the less developed fruit in favor of a heartier fruit. This does not mean that I am a bad gardener, but rather – if I pollinated all the fruit correctly then I see this as the process by which the squash plant is determining its next generation of offspring. A stressed plant in a poor environment may favor the smaller fruit over the larger fruit, to enable it to perpetuate its seed; whereas a vigorous plant in a healthy environment will favor setting larger fruit with vigorous seed. 

Withered squash fruit - this could be a bad thing

When growing squash, it is wise to pick a variety that you can sustain in your garden and your climate. In 2010 I grew Athena (hybrid) cantaloupe in my garden. The vines set so much fruit (at the same time the plant was under intense environmental duress) that the plant literally killed itself. Slow and steady wins the prize: It is better to choose a variety that works in my environment then to pick a variety that produces so abundantly that it kills itself before the fruit matures.


  1. Wondering if you can help me w/ a zucchini problem. I've grown it quite successfully the last 2 summers (after learning about hand pollination), but this year I seem to be having a new issue. I got about 5 or 6 fruits from 2 very healthy looking plants back in June, but starting in July, I noticed the female flowers were beginning to turn yellow before their flowers even opened (so I couldn't pollinate them). The leaves look healthy, and there are no problems w/ the male flowers, so I am wondering if it might be the uneven moisture levels in the soil due to monsoon rains (we seems to have had quite a bit in Oro Valley). I don't have a moisture sensor on the irrigation system, so it always gets watered. Do you think this could be it or do you have any other thoughts?

    1. Dear Josette,

      Thank you for your question. Without a soil test, the mineral content and pH of the soil is really hard to tell. I try not to even pretend that I know all the answers, especially without seeing your soil. However, in the past I have always given my fruiting plants (squash, tomatoes, cucumbers, etc.) more phosphorus than the other two essential minerals. The phosphorus is the P in the N-P-K of fertilizer.

      A few years back, one of my zucchini plants was not producing any female fruit. I scratched some bone meal (usually high in phosphorus) into the soil about 6" from the main root and within a week the zucchini was producing female fruit and within 1-2 weeks I had fruit setting. If you attempt to do something like this, try to amend the soil on a night when you water. Severe heat coupled with adding nutrients can cause plants to be more sensitive to the heat (kind of like an Arizonan eating lunch, then going outside without having enough to drink).

      I have heard that both phosphorus and potassium can build up in the soil over time. With that in mind it is often helpful to give the plant a good dressing of finished compost around the area where the plant is rooting.

      Two other possibilities could be that the plant has lived its life and won't give any more (not likely with healthy looking leaves) or that you have some squash vine borers near where the fruit is setting. If you are not familiar with Squash Vine Borers I have some pictures of them on a previous post:

      I hope you are able to bring your zucchini back to life, Josette!

      Wishing you the best during the last stretch of our summer gardening season!


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