The key to long-term success against garden pests and diseases is prevention, but until we begin gardening, it's impossible to know what to prevent! For example, many suburban backyards are now routinely grazed by deer, but until you plant a few choice shrubs and perennials, you might not realize just how much damage they can do in a single night's feeding. Birds are a delightful presence until they discover your berry bushes. And insects are always tricky, because many are highly beneficial to the garden, while others wreak havoc. Here are a few guidelines for dealing with some of the most common pest and disease problems.
Wild animals and rodents can destroy a garden in no time, and the biggest offender (both in size and potential damage done) is deer. There are countless deer repellants on the market, from motion-detection sprinklers to warning scents, but the sad truth is that nothing short of a fence really will protect your garden from a herd of hungry deer. Fortunately, if you simply need aboveground coverage, strong net fences can be used in place of wooden or metal structures to preserve your view of the woods and save you money. If you need underground protection from burrowing intruders as well, you might do better to invest in a deep fence.
Many plants are advertised as "deer proof" or "deer resistant," and while a starving deer will eat just about anything, choosing plants that are naturally distasteful to the herd is certainly wise. Poisonous plants such as Taxus, Prunus, Rhododendron, Calluna, Cestrum, Delphinium, Helleborus, Lobelia, Aconitum, Physalis, and Digitalis are among the very last to be nibbled by any creature. Spiny plants from Yucca to wild roses all fare well. In the bulb garden, Narcissus is left alone by most burrowing rodents, and some gardeners plant their Daffodils several feet wide all around beds and borders to create a natural barrier that may discourage underground rodents.
If you are not able to build a fence but need good protection from animals, consider growing a "living wall" with dense evergreens such as Thuja. By planting the trees slightly closer together and in two staggered rows, you can make garden entry very difficult for larger animals. Of course, the trees will take several years to grow tall and broad enough for good coverage, so during that time you may need to use netting and other protection for your plants.
Not long ago gardeners routinely sprayed against many insects, but now we try to avoid many if not all artificial toxins in the garden. This can make the control of destructive insects a challenge, but not an impossible task.
First, always practice good hygiene in the garden. Many insects live and breed in the debris in garden beds and borders, so make the quick clean-up of fallen leaves, cut twigs, and other garden litter part of your garden routine.
Second, keep an eye on your plants. Turn leaves over and see what's lurking on the underside. Again, not all insects are harmful by any means, so at first simply observe. Then, if you begin to see holes appearing in the foliage or other signs of damage, try to identify the culprit. Knowing the enemy is at least half the battle; once you can look up information about the pest, you will probably find some easy strategies for controlling it. For instance, many insects are at rest early in the day, and a quick walk through the garden with a bucket of soapy water may be all you need to control really troublesome nibblers such as Japanese beetles (just pick them up and dunk them in the water). Many times control is a better goal than elimination, especially if it means you can avoid using harmful sprays and chemicals.
Third, try time-tested home remedies against some pests. For instance, baiting snails with beer traps (available very cheaply and easy to use) can keep your Hostas, Petunias, and other snail delicacies in good shape, especially if you begin early in the season and keep up with it.
Fourth, encourage the natural enemies of your pests. Welcoming birds into the garden with a shallow, clean birdbath, feeders, and even houses is a very effective way to reduce the insect population. And many "good bugs," such as wasps and bees, not only pollinate the garden, but destroy some harmful insects.
Fifth, grow your own repellants. Onions are the traditional best friends of roses in the garden, and also make a nice perimeter planting around the veggie patch, where their strong scent repels certain pests. Some gardeners even plant "trap crops" to attract a pest, thus keeping it away from more valuable plants elsewhere. Mirabilis (Four o'Clock) draws Japanese beetles, for example, which can keep them from settling on the roses. However, some gardeners believe that encouraging the presence of a pest in the garden at all is a mistake, so this strategy is controversial.
Plant diseases tend to be fungal, bacterial, or viral, and many can be prevented or easily controlled. Mildew is a big problem in humid and wet climates, while leaf spot, rust, and other infections can occur anywhere. Viruses tend to affect the entire plant, and often the only solution is to uproot the plant and destroy it. Never add any part of an infected plant to the compost heap or let it remain within the garden. These infections can be spread by air.
Good garden hygiene is again a key to keeping plants healthy. Remove debris promptly, and watch the crowding of your plants. If the foliage is overlapping, it may create wet pockets that can breed fungus. And if one plant in a tightly-packed bed or border becomes infected, the disease will spread rapidly. Spacing plants a bit farther apart not only reduces the risk of infection, it also improves air circulation for the entire planting, which prevents some of the conditions (standing moisture, heat) that create problems in the first place. Pruning shrubs and trees to create a more open habit has the same effect.
If you live in a humid or wet climate, try to water the garden very early in the day, to give the moisture a chance to absorb or evaporate before nightfall. Few plants like standing water on their foliage or at their crown, and mildew can develop very quickly in these conditions.
Finally, whenever possible, plant native species. These are largely untroubled by pests and diseases, and tend to be tolerant of (able to withstand) those they do attract. Over hundreds or even thousands of years, these plants have developed ways of flourishing in spite of the animals, insects, and diseases that might afflict them. You will find them much easier to care for and quicker to establish in the garden.