Summer squash are prolific plants, often producing more flowers than the plant can support. When this happens, the excess flowers will naturally fall off.
The first flush of flowers is usually male, followed a week later by the female flowers. Do not be alarmed when these first flowers fall away. This is only a problem if most or all of the female flowers are lost.
When all flowers are lost, the problem is usually a problem of excess rather than lack. An excess of fertilizer, moisture, temperature or the excessive use of insecticides is usually the problem.
Perform a soil test to determine fertilizer needs. Use a complete low nitrogen fertilizer like 5-10-10 before planting.
Distinguish between male and female flowers. Male flowers lack the swelling of the ovary at the base of the blossom. Male flowers drop after producing their pollen while female flowers should remain to produce fruit.
Look for signs of pollinating insects. Flowers that are not pollinated will drop along with their tiny fruit. Pollinate by hand if insects are not present by brushing inside a male flower with a paintbrush or cotton swab to gather pollen, then transfer it to the female flowers by brushing inside them.
Protect squash flowers from high winds, if possible, and avoid excess moisture. Water squash in the morning as needed.
Use a shade cloth during the hottest part of the summer. Blossoms are lost due to extreme heat. In tropical areas, plant squash in the early spring and fall.