Gardeners have a lot of potential problems to worry about with their plants. There are weeds, weather trends, animals, insects and a variety of diseases. By starting off on the right foot you can at least limit the initial exposure to disease, helping to reduce the danger of later disease issues.
The first step is understanding how diseases are introduced to your garden. Some diseases find their way into a garden as spores, blown along on the wind, while others come to the garden via insects that carry the bacteria or virus from plant to plant while they feed. Even more diseases could be laying dormant in your soil before you even decided that you wanted to plant anything. Seeds or young plants introduced to your garden soil could also be carrying disease, and in planting you could be sowing the seeds to disaster without ever knowing. This could lead to seedlings dying before they even emerge from the soil, or growing for a short while and then developing the signs of illness. If any disease is not spotted quickly the virus, fungus or bacterium at the root of the problem could quickly become nearly impossible to eradicate. While all those dangers are formidable, do not panic. There are several things you can do to get off to the cleanest start possible.
Seeds are a simple first step. If you think about it, no seed company wants to be known as one that sells problems. Therefore, most reputable seed companies have some level of screening program in place to prevent diseases from being sold in their seed packets. To be certain the company you plan on buying from does adequate screenings, do some research. Check their website or read their seed packets to see how comprehensive the program is. It is also valuable to check whether the company treats their seeds with hot water to kill disease organisms. If you are using seeds that you have collected from previous harvests, or via seed swap from a fellow gardener, there is certain a level of disease risk. Be certain to harvest seeds from the most vigorous and healthy plants.
Seedlings and other plants purchased from a garden center, nursery, or any other source should be labeled with a warning label. Just because the plant appears to be healthy, there are no guaranties. They could seem healthy because of the pampered life they might have had thus far in a greenhouse. Since you have no knowledge of the seeds that were used to grow these plants, or the soil, you have no idea of it they could have been infected with something from the start. If they have been infected with something they will likely show symptoms only after you have gotten them home, and introduced them into your garden soil. One way to lessen this risk is to buy your plants from a trusted, local grower. The option with the least risk is to grow your own seedlings from clean seed and use your own transplants when the time is right.
Now, as you might have guessed, staying completely disease free is sometimes nigh on impossible. However, there are many more plants out there that have been bred to be disease resistant. This does not mean that they will suffer no ill effects from infection or illness, but they are better able to fight off the miniscule invaders. If you have a specific issue that has plagued your gardens and know what you are most likely to have to battle, then you can seek out plants bred to be resistant for the particular infection. If a specific evil has been rampant in your general area for the last few years, even if it has not hit you yet, you could avoid some of the heart ache involved in losing crops. This is not a complete solution, since there are several varieties that are now available with resistance to one or two of the most common diseases, there are few that are resistant to my main nemesis, late blight. When in doubt you should always feel free to ask a professional at your local nursery, a representative at your favorite seed company or fellow gardeners for recommendations or suggestion.
While doing your best to avoid issues from the very beginning might not keep all disease away, it can help keep issues to a minimum. Being proactive is the best defensive against disease. Even if you are just getting started, and are building up the soil quality and learning the ropes of gardening, in planting the cleanest seeds and plants as well as the most disease resistant plants you can enjoy a better, less stressful, harvest.