Now that you’ve had a chance to become acquainted with the brassica and allium families from Part I, let’s move on to often-overlooked areas in companion planting.
Other than light, watering, and feeding requirements, also take note of:
- Potential crowding issues
- Root depth requirements of companions
- Planting poisonous companions
- Companion planting as an art, not science
The term “companion planting” can sometimes lead one to thinking it’s OK to create a layout where companions must be in “close quarters” to each other. Remember that, like you and I, even plants need their “space”, so always consult your seed package or a good gardening book to ensure that you give lots of growing room to your plants. Spinach is often taken for granted with respect to its need for space (yes, we have bungled growing spinach in an area where it thrives – due to our ignorance!). Ideally, 6 in. spacing is desireable to grow large, healthy leaves.
Newer gardeners will often plant indeterminate tomatoes like Early Girls too closely together. Crowding not only affects yield, but also ease of harvesting as you maneuver around neighboring plants. Ideally, it’s good to know the approximate root depth of your plant species (Ref. 1, p.79) and provide plenty of nutrients at different levels in the soil. If you don’t give plants space that allows their roots to flourish, then yield may be impacted regardless of the companion effect.
We recently came across a companion planting book recommending foxglove (Digitalis purpurea) as a companion plant to potatoes, tomatoes, and apple trees for its growth-stimulating and antifungal properties. But it failed to mention that this gorgeous plant, containing digitalis glycosides commonly used to treat congestive heart failure, can be lethally poisonous from ingesting any part of it – roots, stems, leaves, flowers, seeds, and sap. The same author suggests larkspur (Delphinium sp.) whose leaves are poisonous to aphids, thrips (and incidentally, humans, as well). So while many plants may be useful companions to your edible garden, be aware of their potentially toxic characteristics (Ref. 2, p. 172) !
Lastly, credible sources like Cornell University’s Dept. of Horticulture, enjoin gardeners not to hang on to every word found in a CP guide as providing foolproof solutions. Experts encourage us to frequently check our plants (go ahead, look under the leaves!) and document observations from our own plant combinations.
Selecting a companion gardening book can be a daunting. There’s just so much out there! However, Anna Carr, author of Good Neighbors: Companion Planting for Gardeners, appears to have done the most thorough review of both the “traditional/folklore” vs. “research” basis of companion planting for the most common and even obscure garden plants. She also offers experimental garden layout and plant combination techniques for gardening geeks to try out in our gardens. Her book should be available at your public library or used at online book sites. It is unfortunate that this book is not being updated with more recent scientific research, but the principles of CP still apply to this day.
- Carr, Anna 1985. Good Neighbors: Companion Planting for Gardeners, Emmaus, PA: Rodale Press.
- Riotte, Louise1975. Carrots Love Tomatoes, Pownal, VT: Storey Publishing.
- Little, Brenda 2008. Secrets of Companion Planting, Sandy, UT: Silverleaf Press
- Smith, Edward C. 2000. The Vegetable Gardener’s BIBLE, North Adams, MA: Storey Publishing