6 Essential Steps to Prevent Disease in an Organic Garden
Disease is one of the less glamorous aspects of gardening, but every gardener is going to see it at some point. Some plant diseases are a minor setback, while others can cause total crop loss.
Conventional and commercial gardeners have synthetic fungicides at their disposal to prevent disease, along with potent pesticides to wipe out disease-carrying insects (and, like, everything else they come in contact with). If you want to grow food without questionable chemicals, what can you do?
There are a ton of natural concoctions out there for treating plant diseases. Baking soda, Neem oil, diluted milk, apple cider vinegar, essential oils, you name it. Anyone who’s been gardening organically for any length of time has probably tried at least one of them. You’ll quickly find out that most of them aren’t super effective, especially once disease symptoms have already started.
For dealing with disease issues in an all-natural garden, it’s important to know why it happens and take preventative steps, rather than just replacing conventional fungicides with homemade sprays whenever you see symptoms.
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1. Fertilize to Support Your Plants’ Health and Immunity
The truth is, we’re usually expecting our vegetable plants to grow in less-than-ideal conditions. Most of the vegetables we like to grow aren’t native, and they’re not exactly equipped to handle wild temperature swings, sweltering heat, and regular torrential downpours from summer thunderstorms. They also have a higher nutrient demand than native plants.
Like people, plants need proper nutrition to stay well when the going gets tough. Environmental stress combined with nutrient deficiency makes plants much more vulnerable to disease. That’s why supporting your plants’ immune systems through feeding is hands down the most important part of disease prevention.
We can’t control the crazy weather. But we can make sure our plants are healthy enough to tolerate some stress without getting sick.
The Problem with the Compost Only Approach
With the recent popularity of permaculture methods like no-till gardening, there’s a pretty widespread belief that you don’t need to fertilize if your soil is healthy and you’re using compost. If plants in the wild survive that way, surely our vegetables can too, right?
Well, wild plants have had the opportunity to adapt over time to work with the resources available in nature. On the other hand, vegetable plants’ genetics have been largely controlled by humans. We’ve bred them to grow faster, grow bigger, and yield larger fruit, all at the expense of survival traits. That means they need a little extra help to thrive and produce to their full potential.
Compost is awesome for your garden, since it supports beneficial soil organisms, conditions your soil, and feeds your plants. But since veggie plants have those unnatural growth habits, they’ll suck up a ton of nutrients in a way wild plants don’t. Compost on its own doesn’t release nutrients quickly enough to keep up with that demand.
What fertilizers can you use to prevent nutrient deficiencies?
You can buy balanced fertilizer blends or organic granular fertilizers that are already ready to go, or you can round up the ingredients to make your own. Vegetable plants need the three main macronutrients nitrogen, phosphorous, and potassium, which is represented by the NPK label on fertilizer products. They also need micronutrients like calcium, magnesium, and iron. Here are a few examples of good organic soil amendments:
-Blood meal and feather meal provide nitrogen (NPK 12-0-0).
-Bone meal is a great source of phosphorous (NPK 3-15-0).
-Naturally-derived Potassium Sulfate (NPK 0-0-50) and Langbeinite (0-0-22) are good sources of potassium. If you want to be 100% certified organic, look for the OMRI label on potassium sulfate products.
-Magnesium sulfate (Epsom salt) provides magnesium. Some gardeners use it as a foliar feed for plants that have signs of magnesium deficiency.
-Manure from grazing animals (cows, chickens, rabbits) makes a good balanced fertilizer when properly aged and composted.
The key to using organic fertilizers is to apply them at planting time (or several weeks before) so they’ll be available to your plants when they kick into high gear with vegetative growth. Most organic fertilizers take at least a month to break down in the soil into nutrients your plants can use.
Fish emulsion (NPK 5-1-1) is a great immediate-release organic fertilizer option that’s high in nitrogen and full of trace minerals. It works perfectly as a quick pick-me-up for plants that are suffering from nitrogen deficiency.
Compost and native soil usually provide plenty of the important minerals such calcium, iron, sulfur, and zinc without the need for adding extra. Deficiencies in these are most often caused by watering issues (too little or too much) or pH imbalances.
Soil Testing for Fertilizer Needs
Before you start adding heavy amounts of organic fertilizers to your garden, it’s good practice to do a basic soil test. Then, you can focus only on what’s needed when you fertilize, which saves you money. Also, soil testing can help you avoid creating nutrient imbalances, which can hinder plants from absorbing other critical nutrients. For example, if your soil already has a lot of phosphorous, adding a whole bunch more may lead to nutrient lockout.
Soil tests are really affordable if you avoid the gimmicky kits. In most areas, your county agricultural extension office will do a basic test for around $10. This is all you need to get an idea of what you should focus on when choosing fertilizers.
Soil pH and Nutrient Absorption
Your soil’s pH is also important for plant health, since it needs to be within a certain range for your plants to access those nutrients you’re giving them. Most vegetable plants like the pH anywhere between 6 and 7. If your garden still struggles with disease and deficiency even though you’re fertilizing, you may want to check your soil pH.
That same basic soil test will give you an accurate pH reading. You can also buy soil pH test kits at garden centers, but I’ve found those are not too accurate, when comparing the results with my professional soil test.
Plants are fairly adaptable when it comes to pH, so a pH of 5.7 or 7.2 is nothing to really worry about. Adding some compost once or twice a year works to keep the pH in balance. If you’re looking at extreme numbers, though, look into amending with pH adjustors like sulfur or lime to prevent nutrient lockout problems.
Keep in mind that successfully adjusting an out of whack soil pH requires some planning ahead. Amendments like lime won’t make much difference for plants you’ve already got growing. You’ll need to apply them in the off season so they have a few months to work before you plant again.
2. Make Sure Your Soil Drainage is Top Notch
Standing water or waterlogged soil can suffocate roots, hinder nutrient uptake, and stress out your plants. It also creates ideal conditions for fungal attackers like Fusarium wilt or other root-rotting pathogens to set up shop. These are a few ways you can improve soil drainage:
Add compost or other organic material to your soil.
Native soil that has lots of clay and not much organic matter tends to hold onto water, so adding that missing ingredient can help improve soil structure and drainage. You can either till it in or take a “no-till” approach by layering it on top and allowing it to work its way down over time.
Shredded leaves are a free resource that do a lot for soil structure. If you decide to till them in, don’t overdo it, and add them in the fall so they have time to break down before you plant anything. Otherwise, they may cause nitrogen deficiency in your plants.
Plant on berms, mounds, or raised rows.
If your garden is in a low spot and tends to stay soggy after a big rain, keep your plants elevated by creating berms or mounding the soil in your planting rows. That way, they don’t sit in standing water. The old-timers have been using that trick for years in areas with dense or clay-heavy soil.
Consider no-till gardening methods.
Sometimes, deep and frequent tilling can worsen soil compaction, leading to more drainage issues. This is particularly true if your soil has lots of clay. No-till methods improve soil structure, aeration, and drainage in a more permanent way. This is a good alternative to spending a small fortune for raised beds if your soil situation is less than ideal.
Never put potting soil in raised garden beds.
This is an understandable mistake a lot of new gardeners make. Since potting soil is meant for small containers that are prone to drying out super fast, it often contains ingredients that make it retain moisture like a sponge. Put that in a big raised garden bed, and it’ll stay waterlogged for too long at a time.
Instead of using potting soil, fill your raised beds with a blend of 50% topsoil and 50% good quality compost. There are other fancier recipes out there you can try, but the 50/50 blend is a fine starting point.
3. Follow Recommended Plant Spacing Guidelines
Planting things too close together can lead to disease for a couple of reasons. First of all, plants that are too crowded will compete with each other for nutrients. Chances are, no one will get quite enough.
Secondly, your plants’ foliage can start to get cramped, as the plants get bigger. This creates a lot of shady pockets, and fungal and bacterial diseases can take hold much more quickly in spots that don’t get much light and airflow.
It’s tempting to cheat a bit on spacing, especially if you don’t have a whole lot of room. You learn when and how much you can bend the rules with experience, but for the most part, it’s best to stick with the recommended spacing on the seed packet or plant label. One tomato plant with plenty of room will produce about the same amount of tomatoes as two plants that are in each other’s personal space. Plus, it’ll be much less likely to get sick.
4. Control Weeds in the Garden
Weeds can host a lot of common fungal and viral diseases, which can then spread to your plants via wind, water splash, or insect feeding. Wild nightshades like horse nettle, for example, are often infected with Alternaria (early blight), which can do a number on your tomato plants. And funny enough, in my garden, these jerks’ favorite place to grow is right next to my tomatoes.
So, yes, weed control is necessary for more reasons other than just keeping your garden looking pretty. Unless you just enjoy pulling weeds all the time, I recommend taking some preventative measures to slow them down.
Mulching your garden beds is a good place to start, since mulch reduces the amount of weeds that pop up. Cardboard or newspaper underneath that mulch layer will take it a step further. You’ll want to get it laid down right before winter so it’ll break down enough you can plant through it by spring.
5. Preventative Sprays: Biofungicides and Liquid Copper
I’ve never had any luck with the baking soda thing or other homemade recipes for disease prevention, but these two organic-approved products are worth your time:
-Biofungicides are friendly bacteria that make it harder for harmful organisms to take hold, once they’ve colonized on your plants’ foliage. Most biofungicides come suspended in a liquid solution you can mix in a garden sprayer and apply to plants. One I’ve found to work well is Monterey brand’s Complete Disease Control.
-Liquid copper fungicide disrupts the cellular processes of fungal pathogens and bacteria. White it isn’t technically organic, it’s considered safe and non-toxic enough to be OMRI-certified, which means it’s allowed for growing certified organic crops. You have to be more careful with this one, since it can burn your plants if you don’t dilute it correctly.
While either option is not enough to prevent all disease issues on its own, these sprays can be a helpful part of your strategy to protect more vulnerable plants, such as tomatoes. They work best if you apply them before disease happens. If you have a lot of trouble with certain plants catching disease, take notes on when it usually strikes so you can spray them beforehand.
6. Identify and Control Insect Vectors
Some of the worst plant ailments, like viruses and bacterial wilt, are brought to your garden via pest insects. These bugs pick up the virus or bacteria from feeding on weed hosts. Then, they spread it to your plants when they stop by for a bite.
Aphids and thrips can transmit devastating plant viruses. Spotted and striped cucumber beetles carry bacterial wilt, which can wipe out a squash or cucumber plant in a matter of a few days. Seeing high numbers of these bugs mean you need to hatch a containment plan, stat.
You can keep thrip and aphid populations down by treating the affected areas in the garden with an insecticidal soap solution a few times a week in the spring, since they’re small and soft-bodied. No need for broad-spectrum stuff like Spinosad or Pyrethrin, which are harmful to good bugs, too. You can also use companion plants to attract predatory insects. Dill, especially when you allow it to bloom, attracts ladybugs and parasitic wasps, both of which help control the little bad guys.
Cucumber beetles are harder to deter. The most foolproof way is to cover young cucumber plants with insect netting to exclude the beetles. You’ll have to take it off so pollinators can work once they start to bloom, but bigger, established plants are better at fighting off disease than young transplants. I don’t have trouble with cucumber beetles in my garden (yet), but I’ve heard of folks having success dusting the plants with Kaolin clay to prevent beetle nibbling.
See this post for more eco-friendly pest control ideas: 6 Natural Pesticides for the Garden + How to Protect the Good Bugs While Controlling Pests.
Disease is never completely avoidable in a vegetable garden, no matter how hard you work to prevent it. All it takes is a period of too wet, too cold, or too hot weather, and you’ll have a few plants that inevitably come down with something. But supporting your plants’ health from the start and taking other prevention steps does a whole lot to reduce the impact common diseases can have on your harvests.
