Don't Plant These Vegetables Close Together

Most of us don’t live on farms with acres to spread out crops, but instead have a few boxes, planters, or a small plot to grow our gardens. As a result, we tend to cram as much as we can into the space. It's called “crowdscaping,”  and not only does it stop plants from growing to their full potential, but it also risks an even bigger problem: cross pollination.

Bees and other pollinators are indiscriminate little flirts. It’d be nice if they took pumpkin pollen and made sure to visit other pumpkins first, but they move onto the next flower whether that's a tomato or dill. Usually, it isn’t an issue—pea pollen has no effect on tomatoes, for instance—but that isn’t always true. Some crops can cross pollinate, and the result is a plant with DNA characteristics of both parent plants. In other words: frankencrops.

Let's take corn, for example. Unlike most plants that rely on pollinators like insects, corn is pollinated by the wind. Corn plants grow tassels, which have pollen on them, and the wind blows the tassels and sends the pollen to fall on corn plants of the same variety. That same wind can carry corn pollen as far as a half mile (but generally, 20-50 feet is considered the usual distance, to be safe). In a home garden, you need to have enough corn in a block to have it pollinate itself (a six foot by six foot block is advisable), but you shouldn't plant multiple varieties of corn in your garden because the resulting ears can take on traits from both varieties, and it won't necessarily be the best traits of each. You can also control cross pollination by choosing two varieties that have wildly different periods of pollination, but that's tricky math to master, as pollination phasse are a result of many factors, most of which are beyond our control. 

How to prevent frankencrops

Unlike corn, cross pollinating squash will affect next year’s crop instead of the current one. The vegetables formed by cross pollination won’t be altered, but the seeds will be. If you save seeds and plant them, next year’s crop will have traits of both parent squashes. I’ve seen it in practice, and it can be both interesting and frustrating: Friends grew mammoth squash one year, each weighing in over 100 pounds, but they were utterly tasteless and watery.

The good news is that this only happens within one species; cucumbers and squash don’t cross pollinate even though they're both cucurbits, for example. The following groups will cross pollinate each other and should be separated by as much as a half mile. Since that's impractical in most home gardens, it’s wiser to simply not seed save these crops:

• Zucchini, Yellow Crookneck, Acorn, Spaghetti, Patty Pan, Delicata, Pumpkins and Gourds, except snake gourds

• Butternut, Buttercup, Banana, Hubbard and Turban squashes

• Muskmelon, Cantaloupe, Charentais; Honeydew; Casaba; Armenian Cucumber; Snake melon (gourd)

Be careful with companion planting

In addition to cross pollination, you also want to consider which plants do and don't benefit from companion or co-planting (planting near each other). Some pairings can have a dramatic effect on how well each plant flourishes. The term for these plants is "allelopathic," which just means they produce chemicals that are problematic for other types of plants. Planting members of the nightshade family (eggplant, tomato, pepper) near cruciferous plants (cabbage, broccoli, cauliflower, kale) risks both plants. However, some plants, like beans, benefit almost every other crop by being nearby. 

As you plan your garden, be aware of how you space your plants and what seeds you save. For some crops, like squash, you want to ensure you are getting every single fruit, no matter how small, into the compost pile so it doesn’t have the ability to sprout. Even if you don’t intend to save seeds, paying attention will prevent you from mangling a crop through cross pollination or bad companion planting.