Companion planting is placing herbs, vegetables or flowers beside each other, to help each other's growth. Plants that are companion planted tend to grow healthier and be more pest and disease resistant.
You need to factor into spring garden planting layouts the concern that some companion plants are not cold weather resistant, like tomatoes. So when planning the layout for carrots, which are beneficial companions to tomatoes, design a fallow space beside the spring-planted carrot bed that you can plant tomatoes into later, when it warms up enough for them.
Or, for better use of space in a small garden, plant other carrot companions that have a short cold weather production season, such as radishes and lettuce. (Lettuce, radishes and carrots are a strong companion team in their own right.) When warm weather makes the radishes and lettuce bolt to seed and become too bitter to eat, remove the last of them, and replace with tomatoes. Remember that tomatoes have a much larger growth habit than either radishes or lettuce, so be sure to allow enough space in your garden layout for tomato plants and support stakes or trellising for them.
Asparagus, which is perennial, also does well beside tomatoes, though the same weather concerns apply, as it does for another of asparagus's companion plants, basil. However, asparagus also benefits from companion planting with parsley, and what many people aren't familiar with is that parsley is biennial--in climates with mild winters, such as where I live in Virginia, parsley will winter over, going to seed in the following summer. I have two very productive parsley plants growing in my own garden at this moment, so I can verify that they do indeed survive winter when the roots are mulched.
That means that planting parsley beside the asparagus bed and wintering it over will yield not only early fresh greens for your salad, it will give the asparagus a companion plant that's also growing when the asparagus is producing stalks in the spring. (Planting tomatoes and basil nearby the asparagus bed will benefit the asparagus roots during the summer as well.)
Other spring planted vegetables that grow better when planted together are:
Cabbage family:Broccoli, brussels sprouts, cauliflower, kohlrabi--Plant with potatoes, beets and onions.
Cabbage family plants also benefit from planting near aromatic perennial herbs such as chamomile, lavender, mint, rosemary, sage and thyme, because aromatic plants are deterrents to cabbage worms. As these plants begin leafing out again in spring, this is protection for your cabbage family plants while the weather is still too frosty for marigolds.
Carrots: In addition to peas and lettuce, they also benefit from being near chives, peas, leeks, onions, rosemary, and sage.
Lettuce: Carrots, peas, radishes and strawberries make good companions.
Onions: Plant near beets, lettuce and strawberries.
Chives benefit carrots and fruit tree roots.
Horseradish nurtures potatoes.
Leeks benefit from onions and carrots.
Peas benefit radishes, and the nitrogen they add to the soil benefits many other vegetables.
Potatoes like horseradish and cabbage.
Radishes benefit carrots, lettuce and peas.
Spinach and strawberries help each other.
So work with plant companions when designing your garden, and reap the benefit of healthier and more vigorous crops.
This article © 2000-2014 Peg Fisher, used by permission.