In the Garden:
Southwestern Deserts
July, 2010
Regional Report

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Volunteer sunflowers sprout amidst a vigorous zucchini plant.

Troubleshooting Summer Squash

Soft-shelled summer squash vines, such as yellow crookneck, pattypan and zucchini, are rampant growers in warm weather. Although fairly trouble free, sometimes squash may exhibit problems. Here's what to do:

No Fruit
If vines do not set fruit, the problem may be a lack of pollinators. Try hand-pollinating your squash. Use a small paintbrush or cotton swab to rub pollen from male flowers to female flowers. Female flowers have a small swollen area at the base, which will become the future fruit.

Wilted Leaves
Two possibilities may cause the large leaves of squash to look wilted. If wilting occurs late in the day, don't automatically apply more water. Evaporation may be faster than the plant's ability to absorb and replace water, causing wilted foliage even though there is plenty of soil moisture. Pouring on more water, a natural reflex when we see wilted foliage, promotes root rot because saturated soil eliminates oxygen, which plant roots need to thrive. Wait until the next morning; if foliage is no longer wilted and the top layer of soil feels moist, watering isn't needed. Add a fresh layer of organic mulch to the bed to help maintain moisture. When you do apply water, make sure it soaks deeply through the root system.

Another potential cause of wilting is the squash vine borer, which also hits other vining crops such as cukes and melons. Adult moths lay eggs on stems near the plant base. After the eggs hatch, white caterpillars with brown heads tunnel into the stems to eat. They cause vines to wilt, even though they are well watered, and eventually the plant will die. Look for entry holes and sawdust-like droppings at the base of the plants. Slit the stem lengthwise from the hole toward the tip of the vine and remove the caterpillar. Cover the stem with soil and it may reroot.

Squash Rotting
Consider several options. If baby squash are just emerging and then rot, it could be that female blossoms weren't pollinated. Hand pollinate as described above.

Another possibility is a nutrient deficiency. Plants need phosphorous to produce flowers and fruits. A side dressing of fertilizer high in phosphorous (the middle number) may help. Organic sources of phosphorus, such as bone meal and rock phosphate, are slow to move through the soil and break down into a form that roots can absorb. Applying them in midst of the season may be too late for this summer's crop, but if you are an organic gardener, try scratching them into the soil at the side of the plant so they are closer to the roots.

Finally, the wet scar formed when the flower detaches from the fruit is a prime site for infection if conditions are right. This isn't a significant problem in the arid Southwest, but be sure to apply water slowly at the soil level, not by overhead sprinkling. (Wet foliage enhances the spread of disease.) Growing vines on a trellis to improve air circulation can help if you deal with humid growing conditions.

Insufficient Friends and Neighbors
Summer squash is prolific. Harvest frequently when squash is young and tender to keep vines producing. If your Godzilla-like squash plants produce more than you and everyone you know can use, donate to a food bank. Another option to reduce the crop is to pick the flowers. Squash blossoms are edible and they make an eye-catching garnish.


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