Every spring I’m frequently asked two questions by gardeners in northern states. The first is, “Why doesn’t my zucchini grow? It just sits there. What’s wrong with it?”  The second common question I get is, “What’s wrong with my zucchini (or cucumber, or melon)? It has lots and lots of flowers but no fruit. What’s up with that?”

Home gardeners love to grow members of the squash family, the Cucurbitaceae, called cucurbits for short. This big, important family includes all types of squash: winter (like acorn and butternut), and summer (like zucchini). It also includes cucumbers, pumpkins, melons in the genus Cucumis (cantaloupe, Persian, honeydew, casaba) and watermelon, in the genus Citrullus.

Keep in mind one very important fact about all these delicious vegetables and fruits:  they are all warm season crops. This means that they are sensitive to cold temperatures. And this sensitivity can cause stunting and lack of fruit.

Vegetable starts of warm season plants are readily available in nurseries and garden centers early in the season, when temperatures are really still too cold for them to thrive. As a result, when gardeners plant them too early, the plants simply sit, growing slowly or not at all, and become stunted. They usually begin to grow well when the weather warms up. So the answer to the first question is the squash doesn’t grow because it is still a bit too cold for it.

These two summer squash, each about 3 inches tall, wait for warmth. They’ve not grown significantly in the two months since they were planted. The photo also illustrates the second problem that crops up this time of year. Both plants above are flowering, but all the flowers are male. Male flowers do not make fruit. Only female flowers make fruit. All members of the squash family have female and male flowers on the same plant, but they produce only male flowers early in the season while temperatures are still cool. They start producing female flowers later in the season.

Here’s a female cucumber flower. See the spiny baby cucumber holding this flower up? That fat spiny structure below the petals (that is, closer to the plant) is the ovary of a female flower. The ovary is the thing that matures into a fruit, whether it’s an acorn squash or a zucchini. No female flowers, no fruit! And that’s the answer to the second question.

Look at the stalk holding up this male zucchini flower. It doesn’t look like a miniature zucchini at all. That’s because it isn’t. This stalk is merely a stalk. This flower does not have an ovary because it is a male flower and it will never mature into a fruit. The male flowers produce the pollen needed to fertilize the female flowers.

A female flower of a yellow summer squash clearly has a large yellow ovary underneath the flower petals. The ovary looks like a miniature squash. After the female flower gets pollinated it matures into a delicious squash.

 Next time you wonder why your cucurbit plants sit and sulk, or your zucchinis make flowers but no fruit, just be patient. Keep your vegetable starts where they are warm and have plenty of sun. Put them outside in the garden or a container when the weather warms up.

David Deardorff

It’s time to get started on the vegetable garden for the coming season so you can grow your own healthy, organic food again this year. Many of us have already started seedlings indoors to transplant out to the garden or the cold frames as soon as weather permits. Kathryn and I have come up with a checklist of ten things to consider before you plant. Each item on the list helps to prevent pests and diseases in your vegetable garden. All ten of them acting in concert really gives you a leg up for a successful and productive year.

1. Sanitize. If you didn’t get around to cleaning up old left-over garden debris last autumn, do it now. Pay special attention to any dead plant material from diseased or infested plants and get it out of your garden. Fungal spores, insect eggs, and bacteria lurking on old infected dead leaves lying on the ground can quickly infect your new plants and ruin your produce all summer long.

2. Right plant, right place. Be sure and read the instructions on the seed pack or the vegetable start plant label and put your plants in the best location to meet those requirements. If your plants have the right amount of light and water, the correct temperature, and the proper soil they won’t be under stress. And stress, as we all know, predisposes our plants (as well as ourselves) to attack by pests and diseases.

3. Light and air flow. Most vegetable and fruit plants want full sun and free air movement. Plants that do not get enough sunlight will be weak and spindly, and won’t be able to produce very much food for you. Free air movement helps foliage dry quickly and helps to avoid diseases and pests so don’t crowd your plants, give them space.

4. Genetic resistance. If you have a choice, choose cultivars that are genetically resistant to diseases and pests. Less disease and fewer pests means less work for you and more produce. Sounds like a win-win to me! Most all of these disease resistant cultivars have been developed through traditional plant breeding techniques.

5. Manage water. Set up your garden so that your watering practices deliver water to the root system, not to the leaves. Keeping the leaves dry goes a long way to avoiding diseases. In general, keep your plants evenly moist for best results. Allowing your plants to get extremely dry and then flooding them to get them extremely wet results in uneven growth, deformed foliage, and reduced yields. Also try to group plants according to their watering needs.

6. Proper temperature. Some vegetables like tomatoes and sweet corn, and fruits like melons are warm season crops. These are plants that flourish in hot humid weather. Other plants like cabbage, lettuce, and spinach are cool season plants that flourish in cool temperatures. If you put warm season plants in the ground in early spring while soil and air temperatures are still quite cool, they will not grow well and may be stunted. Conversely, cool season plants planted in mid-summer may simply flower and set seed while still very tiny.

7. Build soil. Creating healthy, biologically active soil is the best way to build healthy plants. Incorporating dead plant material (not diseased!) into the soil feeds micro-organisms that break it down into simple nutrients that will ultimately feed your plants. Feeding the soil results in a complex ecosystem filled with fungi, bacteria, insects, worms, and other critters that help to out-compete the ones that want to damage your plants. Compost and organic fertilizers incorporated into the soil are excellent sources of dead plant material with which to feed your soil. Mulch placed on top of the soil around your plants will also eventually break down and feed the soil.

8. Polycultures. A polyculture is where you put lots of different plants into the same location. Corn, beans, and squash, for example, is a traditional polyculture developed by the Pueblo Indians of the Southwest centuries ago. The corn, beans, and squash are all planted together in the same bed. You can mix vegetables and fruits into your flower beds and vice versa. The important benefit you get is that it makes your plants harder for pestiferous insects to find. It also makes it difficult for fungal and bacterial disease to jump from plant to plant.

9. Rotation. Don’t put a plant in the same location where you grew it last year. Move your plants around from year to year to make them moving targets. It helps to avoid the build-up of soil-borne pests and diseases. There are lots of crop rotation systems and schemes, you can choose one of these or just create your own system, one that works for you. Many people find that a three-year rotation system works well.

This hornworm caterpillar was eaten alive by a parasite.

10. Beneficial organisms. There are lots and lots of insects and other critters that are willing and able to eat the insect pests that want to eat your produce before you do. Many are predators, like lady bugs and lacewings, and some are parasites that lay their eggs inside other insects. And then there are beneficial nematodes that attack and kill insects that live in the soil. Many birds are also insectivorous and can help to get rid of insect pests for you, and so can frogs, toads, and spiders. If you manage your garden to protect these beneficial critters, they will help you manage the pests.