Every garden season is different. Weather patterns, soil conditions, pest and disease outbreaks all vary from year to year. Even though many gardening variables are largely unpredictable, there are ways to generally decrease pest and disease occurrence no matter what conditions you're up against.
Pests and diseases are opportunistic by nature. They like to exploit already weak plants in poor conditions. Increase your chances of avoiding them altogether by following some best gardening practices to ensure a healthy, strong garden.
Choose the right plant for the right place
The first step you need to take to give your garden the best possible chance to succeed is to choose the right plant for the right place. If you put plants in an environment that fits their needs well, they will likely become healthy and vigorous, better able to fend off insect damage and less likely to become diseased. Proven Winners recommends the following when considering what to plant in your garden and where to plant it. First, choose plants that match your area's general climate well and know your area's hardiness zone. More specifically, take note of how much sun an area gets each day, if the soil holds water or stays pretty dry, and whether the area gets high traffic or not. Then, do some more research on the plants you want to use in your garden to make sure they're a good fit. And don't forget to give your plants enough space to grow. An overcrowded garden can lead to too much competition and stunted plants. Not to mention, poor air circulation as a result of a crowded garden can increase humidity and chances for diseases to take hold.
Pay attention to the soil
Healthy soil equals healthy plants. If your plant is nutrient deficient and struggling just to make enough energy to survive, chances are it won't have the energy needed to deal with pests or diseases. The best way to ensure nutrient dense soil is to add organic matter, preferably rich, organic compost, every year. Also, look into organic fertilizers to supplement with during the growing season, especially for heavy feeders. According to Grow Great Vegetables heavy feeders include asparagus, Brussels sprouts, broccoli, onions, peppers, and spinach. In addition, keep your beds well weeded so unwanted plants don't use up nutrients. Also consider planting a cover crop, such as buckwheat or clover, in between growing seasons to help suppress weeds and rebuild the soil.
Watering well makes a big difference to the overall health of your garden. Here are the main things to keep in mind. As a general rule of thumb, most plants need about 1 inch of water each week. Always check before watering and water when the top 2 to 3 inches of soil is dry, but there's still some moisture below that. Also, a deep watering encourages plant roots to seek the water and they become better-established, stronger plants. If you've made a habit of shallow, but frequent watering, you are encouraging plant roots to stay near the soil surface, which makes for a weaker, more drought susceptible plant. The more stresses a plant has to make up for, the more prone to pests and diseases it becomes. Also, if possible, water early in the morning before dawn. This allows the plants to use the water efficiently, before the heat of the day when most of the water usually evaporates before the plants have a chance to use it. Watering in the morning also allows the plant to dry out completely before temperatures drop at night. Wet leaves during the dark, cooler hours of night favor disease growth. For the same reason, it's helpful to keep the water off the leaves and water only around a plant's root zone.
Rotate your crops
Crop rotation is important for a couple major reasons. First, not rotating your crops depletes your soil of certain nutrients more quickly. For instance, tomatoes are heavy nitrogen feeders. If you plant them in the same spot year after year, the soil may become nitrogen deficient more quickly, or at least require more vigorous amendment and fertilization. Instead, consider planting legumes, which return nitrogen to the soil, after a planting of tomatoes. Planting plants in the same spot every year also makes them more prone to insect damage. Insect eggs often overwinter in the soil, so if you plant their favorite plant in the same spot they are born into a grand feast. A good rule of thumb is to allow two years to go by before replanting a crop in its original location.
Keep a tidy garden
In order to keep pest and disease damage to a minimum, it's really important to immediately remove and destroy any diseased and/or insect infested plant material from your garden. Also, keep your beds weeded since weeds only provide extra cover for insect pests. You should also make sure to clean out any spent or decaying plants. Any pests and diseases that infected a plant while it was alive often overwinter in the rotting plant material. Be very careful not to use any diseased plant material in your compost because many diseases can overwinter in the soil as well and infect your compost supply.
A diverse ecosystem is a stronger ecosystem. Instead of planting one crop all in one place, intermingle them with other crops and herbs. Intercropping increases your chances for success. For instance, if insects find one batch of tomatoes, it doesn't mean they'll find the other. However, if they're all planted in the same place, they are all likely going to be affected. Also, consider using plants like marigolds, which are said to repel insect pests. And even better, try to attract beneficial insects, like ladybugs, to your garden. Mother Earth News recommends filling 5 to 10 percent of your garden space with plants that attract beneficial insects, such as mint, tickseed, comfrey, yarrow, lobelia, and a host of others.