Good Neighbours and Bad Neighbours

Here's what's ahead:

• All in the Family: Why Plant Families Are Important

• List of Plant Families

• Combinations to Avoid

• Tomato, To-mah-to: It's All About Rotation

• Good Neighbours – Diversity is Key

• Plant Substances that Drive Away Pests

• Good/Bad Neighbours Cheat Sheet

• Easy Mixed Cultures to Try

All in the family

It's just like in real life: living next door to your own family can be difficult. Sure, you may think the same way in a lot of areas, and you might like the very similar things. Plants from one plant family also often appear to the gardener to be ideal companions because they have similar requirements in terms of location and care.

But just like in your family, difficulties can arise over the smallest things. Your brother always leaves the Xbox controllers lying about. Mum wants to know what time you'll be home. Dad snores. Sister steals your clothing. And representatives of the same plant family are susceptible to the same diseases and pests. If related plants are too close together, the pests will eat their way through all the rows in your bed.

This means, representatives of the same plant family are usually poor bed partners. When rotating crops, you should also be careful not to plant members of a plant family one after the other.

List of plant families

It makes sense then that you will want to put bad neighbours as far apart as possible in your bedding plan. To make this easier, we have put together an overview of the most important plant families and their representatives in the vegetable garden:

• Nightshade family: tomatoes, peppers, aubergines, potatoes

• Cucurbits: cucumber, zucchini, squash, melon

• Cruciferous vegetables: kale, white cabbage, red cabbage, broccoli, cauliflower, kohlrabi, autumn and May beets, radishes, radishes, horseradish, rocket, garden cress, rapeseed, mustard

• Sunflower/daisy family: lettuce, lettuce, lettuce, iceberg lettuce, endive, radicchio, chicory, chicory, salsify, Jerusalem artichoke, dandelion, sunflower

• Umbellifer family: carrot, parsnip, celery, parsley, fennel, caraway, dill, chervil

• Butterfly plants: peas, beans, lupine, alfalfa, vetch, clover

• Foxtail plants: beetroot, Swiss chard, spinach, garden log

• Lily family: onions, leeks, garlic, chives, asparagus

• Knotweed family: rhubarb, buckwheat, mallow, sorrel

• Mint family: thyme, marjoram, basil, savory, oregano, anise hyssop, lavender, sage, all kinds of lemon balm

Plant combinations to avoid

Cabbage species(cruciferous family) in particular are a popular target for numerous invaders, both by land and by air. You should grow the members of this plant family as far apart as possible, or place them on your balcony. The combination of potatoes and tomatoes is also fatal. Since potatoes serve as intermediate hosts for late blight and brown rot, the tubers will most likely infect your tomatoes if they are affected themselves.

Yes, plants were social distancing before it was the thing to do.

But it's not just physical distance that is critical for containing diseases and pests. We also have to mind temporal distance, also known as crop rotation. There is one simple reason for this: the larvae of many pests hibernate directly at their former feeding place in the ground. So if a member of the same plant family is planted in the same place in the next year, they can just pick up where they left off.

With cabbage plants (Cruciferous family), for example, you should even take a cultivation break of 4 years; during this time you should not grow broccoli, radishes, rocket or mustard. Basically, the goal is to starve out any fungal spores and pests from their food source.

You should also be cautious when it comes to green-manuring with mustard or rapeseed, as they also belong to the cruciferous family. If you use mustard on your entire garden and have a problem with cabbage pests, you will have trouble keeping other, larger cabbage varieties in your garden pest-free in the following growing season.

Celery (Umbellifer family) is just as disagreeable. It doesn't like being planted in the same bed as its own kind, and punishes you with a plant tantrum (a plantrum?) if you force it to wear its older brothers' hand-me-downs.

There are also plants that are completely peaceful to their own kind and that are not easily disturbed by pesky pests. This includes most Mediterranean herbs, but also many local wild herbs and flowers, provided that they feel comfortable in their location. Because everything is better when there is sun and sand.

Tomato, To-mah-to: It's All About Rotation

...which one is correct?

Maybe you've heard that tomatoes are a big exception when it comes to crop rotation and mixed cultivation. Apparently they love to be grown in the same location year after year, and yes - in the greenhouses of many hobby gardeners, it seems to work that way.

But that may be more the result of loving care and a protected location than a general principle. As with all plants, diseases in tomatoes have become specialised in precisely this type of vegetable or plant family. Tomatoes can put up with a lot, and varieties that have just been refined are not as susceptible to pests like aphids, for instance. But at some point, when the nutrient reserves in the soil are used up, the tomatoes need more and more fertiliser and become more susceptible to disease.

Especially if your tomatoes look weak and have light green to yellow leaves, or if you notice signs of late blight on them, then it is high time to change the wallpaper, or just pack up and move entirely. Those nasty spores stay in the ground for years, just waiting for the next tomato to munch on...

Good neighbours: diversity over uniformity

On the other hand, good bed neighbours are usually representatives of different plant families. This is also no wonder, because just like a town or city, the more diverse a plant community is, the better-rounded it becomes. Some plants provide shade, others serve as climbing aids, and still others enrich the soil with nitrogen or other substances from which their bed partners benefit. This cultivation method is called mixed culture.

There are a few things to consider when it comes to mixed cultures, but if you follow one simple principle, you will have a good chance of a healthy and productive garden. Just remember this: the more diverse your plants, the better. This applies both to the varied nutrient requirements of different plant families, as well as to the height of growth and the depth of the roots. Only when it comes to water needs is it important to bring like with like together, just so that some don't drown or starve due to their neighbours' needs.

Plant Substances That Drive Away Pests

Sufficient space, water and nutrients are usually guaranteed in a mixed culture, but a perfect plant partnership is not only based on external appearance and basic needs. So what does a plant look for in order to find its soulmate?

The key is this: Phytoncides.

Sure, that doesn't sound particularly romantic, but it is very relevant for you as a gardener, if you are looking for good partners or neighbours for your plant protégés.

Phytoncides are antimicrobial compounds that come in the form of fragrant and/or liquid excretions and help certain plants have a positive or negative effect on other plants. These include, for example, saponins. Saponins ("like soap foaming substances") have a growth-promoting effect on renewable crops. Some examples of plants that secrete these substances are spinach, garden log, potato, beetroot, tomato, primrose, pansy, globe flower, peony and delphinium.

In symbiosis with nodule bacteria, members of the Butterfly family bind nitrogen in the soil, also secreting a substance called heteroauxin, which promotes root growth, especially in fruit trees.

Flowers like marigolds promote plant health using their immune system. They have properties that kill the parasites in the earth that prefer to eat roots.

The combination of onions and carrots is also popular, the fragrance of which confuses parasitic flies to such an extent that they do not lay their eggs in the onion or carrot.

Many herbs have a positive effect on vegetables with their essential oils:

• They improve the taste: new potatoes taste better with thyme and coriander, carrots with dill, radishes with cress.

• They ward off pests: celery protects cabbage crops from fleas and caterpillars. Thyme, sage and peppermint protect your cabbage plants from cabbage white butterflies and its voracious caterpillars. In addition to beans, savoury acts as a protective shield against lice. Basil, nasturtiums and garden cress protect tomatoes from lice and plant-sucking parasites.

• They encourage growth: dill allows carrots, onions, peas and cucumbers to thrive better, while chervil encourages lettuce to grow.

• They attract pollinating insects: borage is a perfect match between insects and cucumbers/zucchini.

Unfortunately, very little research has been done into this world of plant substances, and it is largely up to us gardeners to discover favourable bedding partnerships beyond these better-known combinations.

Good and bad neighbours: a cheat sheet

If you do not grow plants from one plant family next to another, or one after the other, and instead create a mixed culture that is as colourful as possible, you will have a good basis for a healthy, high-yielding garden.

If you want to exert even more influence, you can use our overview of particularly good neighbours (those who bring cakes) and particularly bad neighbours (the ones who blast their music at 2AM) as a guide. Just avoid the bad neighbours and try the good ones to create your own perfect mixed culture:

Easy Mixed Cultures to Try

There are some very established and popular mixed cultures that we can easily recommend that you try out, even if you a total gardening n00b:

Cabbage and lettuce: Lettuce keeps fleas away from cabbage.

Carrots and onions or leeks: They confuse each other's pests with their scents when they approach. It is best to combine early carrots with onions and late carrots with leeks. Late carrots and onions do not go well together because carrots need a lot of water in late summer to prevent them from bursting, while the onions should stay dry on the bed during this time.

Tomatoes and basil: The perfect combination in your garden as well as on your pizza. Both like it moist; the tomatoes protect the basil and the soil around it from drying out, and the basil keeps aphids away from the tomatoes with its scent.

Corn, beans and pumpkin: This mixed culture is also affectionately know by the nickname "Three Sisters", and was practiced by the Maya and Aztecs for centuries. Maize helps support the growth of beans, which enrich the soil with nitrogen for the other two big-eaters. The pumpkin in turn suppresses weeds as a rampant ground cover and keeps moisture in the soil. Its fruits only ripen in the autumn sun when the beans and corn have already been harvested. Corn and pumpkin should be planted or brought forward a few weeks before the beans in the springtime.

Cucumber and dill: Cucumbers keep the soil moist, while dill keeps pests out and promotes growth. After harvest, this Dream Team harmonises perfectly in a salad as well.