Garden Anecdotes: Truth or Tales?

Rosa 'Wekcobeju' (CINCO DE MAYO™)
Are coffee grounds really beneficial to rose growing? Maybe! Rosa ‘Wekcobeju’ (CINCO DE MAYO™ shown)

There are many garden truths and tales. Growing up, my family subjected me to lots of gardening anecdotes that I simply accepted. My grandfather feverishly sprayed his veggies with odd homemade concoctions, my grandmother insisted that amending her roses with coffee remnants was beneficial, and my aunt claimed that planting marigolds among veggies deterred harmful pests. These are a few of many.
I question whether these and comparable anecdotes have any elements of truth. Are such practices based in truth, or are they simply products of tradition or hearsay? To tackle this matter, I turned to research to pick out truths from garden practice lore.

Creative Pest Deterrents

Bars of soap hanging from trees, carnivore urine sprinkled in beds, pepper spray applied to tulips, and dishes of beer scattered among hostas. These home remedies are weird, to say the least, but do they work?
Folksy remedies to deter deer are some of the most popular, because deer are garden destructors. Soap, sachets of human hair, pepper sprays and urine concoctions are favorites, because deer dislike disagreeable scents and flavors, but effectiveness has more to do with consistent density of coverage.

Capsicum annuum hot peppers
Sprays made from hot peppers have been known to ward off pests, for a while.

Such remedies create a fleeting veil of protection over garden deer treats. For example, scented bars of soap hanging in apple trees are not enough to keep deer from plucking apples, it’s time consuming to keep ornamentals swathed with pepper sprays (though they work), and human hair is a red herring. One method, however has been shown to work. Predator odors can linger, and studies show they ward off prey, such as deer, mountain goats and beavers. So, carnivore urine, though not cheap, works.
Still, the best course of action is to “simply” plant plants that deer dislike—though they’ll eat practically everything in a lean winter. Dogs in the yard work well too.
Snails and slugs are real pests, and beer is the favorite home remedy for their demise, which is great because it works. Slugs love beer’s hoppy, sweetness, but are pickled by its ethyl alcohol. One evening try sinking a half-filled can in the ground near a troubled spot, and you’ll have marinated escargot by morning.
Some tout homemade pesticide concoctions with ingredients like tobacco juice, dish soap, or medications. Stay away from such motley mixes. Certain ingredients may be helpful; soap acts as a surfactant and smothers insects on contact, and nicotine (actually a nasty neurotoxin) is one of the oldest pesticides, but spraying meds on plants, particularly veggies, could be dangerous as well as ridiculously expensive.

Companions or Charlatans?

Marigolds by Jessie Keith
Marigolds can actually ward off some garden pests down below in the soil.

There is a lot written about companion planting, and certainly some plants offer benefits to their neighbors, nitrogen fixing legumes for instance, but can one plant actually deter pests from another?
The answer is, sometimes. Herbivorous insects can pick up the volatile compounds from their host plants from great distances, and a 2005 study conducted in the UK showed that insects can find their host plants when hidden amongst other undesirable plants. This should not be surprising. To survive, they must be able to pick that needle of a plant out of a haystack of others. So, sadly marigolds won’t protect your cabbages from loopers.
Marigolds have been shown to repel root knot nematodes, a real problem with tomatoes, so they do provide natural good down below. (Read more about the power of marigolds in the garden here.)

Odd Amendments

Fafard Garden Manure Blend packThe raised probably raised eyebrows when Native Americans taught them to plant a fish with their corn crops, but we now know that these fishies acted as quality fertilizer (think fish emulsion). Other homemade amendments might offer some help, too.
Take my grandmother’s favorite amendment for roses, tea and coffee. Both are slightly acidic and break down quickly, so essentially they act as quick compost at a pH suitable for roses. So long as its organic, disease or heavy metal-free, it’s probably going to eventually adding some benefit.
But, at the end of the day it pays to amend with proven garden amendments shown to provide sound organic matter and encourage the growth beneficial microorganisms. Fafard’s  Garden Manure Blend, Natural & Organic Compost and Canadian Sphagum Peat Moss are all proven amendments that will make your garden plants shine.
With age I’ve learned to approach anecdotal garden solutions with a healthy dose of scrutiny. But, I also refrain from total disbelief in their power. Even the oddest sounding remedies might do some good. At the end of the day, it’s best to stick with tried-and-true methods and garden amendments and additives proven to work.