Plant lovers are notoriously susceptible to anyone offering a solution that's guaranteed to make their garden healthier, more beautiful and free of pests or disease.

We adore experimenting with household remedies, eagerly blending dish soap and horticultural oil in our attempts to cure our aphid-riddled and black-spot-infested roses.

Jeff Gillman, an associate professor in the Department of Horticultural Science at the University of Minnesota, decided to tackle this issue head-on after years of fielding queries from gardeners about the relative value of home-brewed remedies, alternative fertilizers and least-toxic pest controls so often touted in the media.

Gillman's results are laid out in his book, "The Truth about Garden Remedies: What Works, What Doesn't and Why," (2006, Timber Press, $19.95 paperback). He uses the latest research to reveal the science behind antidotal remedies, explaining in some detail which ones are successful - and why others are not.

Although I don't necessarily agree with all of Gillman's conclusions, his efforts have given us a well-organized book that's filled with a great deal of thought-provoking information.

When this book first came out a couple of years ago, I laid out three gardening theories and/or remedies analyzed by Gillman, along with his conclusions. This column generated a flurry of comments from readers, so I decided it's time to look at three additional theories/remedies - let's see if you agree with his conclusions!

Fact or fiction

n Coffee grounds: Many gardeners swear by the practice of sprinkling coffee grounds around their plants, or mixing it into their compost.

The theory: As organic matter, coffee grounds will break down and prove beneficial for plant growth. Coffee may also contain chemicals that inhibit weed growth and also acidify the soil.

The real story: Coffee grounds contain about 2 percent nitrogen, 0.3 percent each phosphorus and potassium and a few micronutrients.

Different plants respond very differently to the addition of coffee grounds to their soil. Some, like lettuce, seem to benefit greatly from coffee ground-amended soil.

Fresh coffee grounds mixed into the soil appear to tie up nitrogen in some plants, so composted grounds are preferred. Coffee residues do seem to affect acidity when mixed into the soil, but not when used as a top dressing.

What it means to you: It's possible that the allelopathic chemicals present in coffee may inhibit weeds, so it's worth seeing if a mulch of spent grounds proves useful. Such a mulch won't affect your plant's uptake of nitrogen, so it can be safely spread around your favorite perennials to provide added nutrients as the grounds continue to break down.

n Beer as a slug killer: Placing a saucer of beer beside your plants to protect them from slugs might be one of the most well-known homemade pest control measures ever devised. But is it really the most effective method of getting rid of these slimy, destructive creatures?

The real story: Beer traps are actually an accepted way to measure slug populations for scientific studies. The only problem being that certain slug species are attracted to beer more than others. The trap itself is key. If it's poorly designed, you'll attract more slugs than you'll kill. The goal, after all, is to get the slug to fall into a bowl of beer and then, well, since slugs can't swim … you get the picture. Shallow bowls with flared, slick sides are a no-no. Sitting the receptacle on top of the soil is also not a good idea, as all of those party-ready slugs will simply gravitate instead to the nearest clump of tasty hostas or tender lettuce.

What it means to you: Just be certain to set your traps so that the slugs are caught, and not just attracted. Make the top of your trap even with the soil, with the level of beer in the container about an inch below the top of the trap.

This means that the slugs must extend their bodies to drink, thereby falling into the beer. The best containers allow an inch of clearance while still having enough room for about 6 inches of beer.

n Pruning tar and other wound coatings: Spreading a coat of something over a tree wound is a common practice that has been used for generations to prevent insects and disease from entering an open wound.

The real story: Recent studies on the effects of wound coatings demonstrate that they are not particularly useful for reducing discoloration or speeding wound closure.

If a tree appears unsightly because of a wound, covering it is a good way to conceal the damage. Pruning tar, for example, is most commonly recommended for sealing wounds on oak trees because of oak wilt; elm trees, because of Dutch elm disease, and fruit tree species, which are often susceptible to canker-causing bacteria.

What it means for you: This practice is not necessary for most trees (except oaks, elms and fruit trees).