Botanical Cousins: Understanding the Connections Between Your Garden Favourites

by Rachel Bosley March 21, 2025

Have you ever planted your garden and wondered why your kale and cabbage seem to share the same problems? Or why your zucchinis and pumpkins seem to attract the same pests? Or why seeds you saved last year are producing a mystery fruit? That’s because many of the veggies in your garden are more closely related than you might think! Understanding these botanical connections can help you plan a smarter, healthier garden.

Family Matters

Some vegetables may look very different above ground, but beneath the soil (or in a taxonomy book), they are practically siblings. Here are a few surprising garden groups that share a genus, species, or family:

Brassica Bunch (Brassica oleracea): This is the most commonly known example. Broccoli, cauliflower, cabbage, Brussels sprouts, kale, and kohlrabi are all the same species! These veggies have been selectively bred from a wild mustard for different traits, but they remain closely related. This also means you can eat any part of all of these brassicas! If your kale starts to bolt and sends up flower buds, eat them like broccoli. If the leaves on your cauliflower or brussels sprouts are tender enough, eat them like kale. Mustards are also very closely related, sharing a genus.
Cucurbit Cousins (Cucurbita pepo, Cucurbita moschata and Cucurbita maxima): Most pumpkins, zucchinis, summer squash, and gourds all come from 3 species in the same genus. Cucumbers are more distant relatives but they share a clear resemblance to squash plants too.
Nightshade Neighbours (Solanaceae family): Tomatoes, potatoes, peppers, and eggplants are all in the same family, which means they often share pest and disease vulnerabilities.
Carrot Clan (Apiaceae family): Carrots, parsley, fennel, dill, and celery are all relatives, meaning they often attract the same beneficial insects and pests.

Why This Matters for Your Garden

Knowing these botanical relationships isn’t just fun trivia—it can help you avoid common gardening pitfalls! Many companion planting suggestions for what plants make bad companions/neighbours are based on these taxonomic relationships and shared qualities.

1. Seed Saving

Seed farmers have to carefully plan their crops around isolation distances and other measures to prevent varieties within shared species groups from crossing. In order to maintain the traits you like about a specific variety in your home garden, the same considerations need to be made if you intend to save seed that will produce offspring true to that variety.

For example, if you save some seeds from a pumpkin, and plant them the next year hoping for more pumpkins, but the fruits set and turn out to be a cross between your favourite pumpkin and a zucchini, that's not ideal. You will still end up with food that is edible off those mystery plants, but it may not have the taste, texture and storage ability you were hoping for from the pumpkin variety you thought you were growing.

Of course, sometimes it's fun to take a risk and save seeds that haven't been isolated. Then you get to grow out a fun surprise, and experiment with what you create. That's the early stages of your very own breeding project for a new variety. Experimenting in the garden is so much fun!

2. Pest and Disease Susceptibility

Closely related plants tend to attract the same pests. Brassicas are a magnet for cabbage moths, while nightshades often fall victim to potato beetles and tomato hornworms. If you plant all your brassicas in one spot, pests can easily move from one plant to another, creating an infestation buffet.

Fungal and bacterial diseases often target entire plant families. Powdery mildew can rapidly spread through all your cucurbits, and late blight can hit your tomatoes and potatoes in one go.

Spacing out plants from the same family throughout your garden makes it harder for pests and diseases to spread. Instead of planting a whole row of brassicas together, try interplanting with herbs or flowers that can help deter pests.

3. Crop Rotation

Since plants from the same family deplete soil nutrients in similar ways, rotating crops each year prevents nutrient exhaustion and reduces disease and pest build-up. It's not absolutely necessary in a small home garden, but it can help break the cycles of certain pests or pathogens that remain in the soil year to year.

Conclusion: Grow Smarter, Not Harder

Understanding which of your garden favourites are botanical cousins can help you make better planting decisions, and can be fun to look for the similarities as these related plants grow through different stages. By spacing out related plants, rotating crops, and being aware of shared vulnerabilities, you can create a healthier, more resilient garden. So next time you’re planting, think like a botanist—you might just outsmart the pests and keep your plants thriving!

For more explanation on some of the terminology used around garden plants, like open-pollinated or landrace being used to describe a variety, check out our blog post, "Navigating the Terminology Jungle of Seed Types".