How to Prevent Tomato Late Blight Naturally

I believe I have discovered how to keep tomatoes healthy all season long. I can't say with absolute certainty of course (I'm not running a scientific study with controls, and this was an unusually warm, dry year) but, for the first time since 2008, mid-September has arrived with one marked difference: my tomato plants are still producing loads of fruit and flowers, and not a single plant has become diseased. After noting the condition of many friends and neighbors plants, I have concluded that it has indeed been a good growing season. But it is not by accident that my plants are showing off such lush and beautiful growth at a time when most people's are turning yellow and dropping leaves - it seems that a ridiculous amount of research (and trial/error) have finally led me to a simple, natural system for growing healthy, blight-free tomatoes on a farm or garden. I hope that what I've learned can help other growers that have suffered from tomato blight. Perhaps together we can end the use of chemicals on our vegetables, and still get to eat our heirlooms too!

Early stages of tomato Late Blight lesion

Rosemary Oil. Trust me, it works incredibly well as a fungicide (and smells delightful too). I learned about using essential oils one night last summer as I was sitting on my porch, staring sadly at my dying tomato plants and wishing there was something I could do to stop the blight from destroying them. Suddenly, a lightbulb went off in my head - essential oils are powerfully anti-fungal! Within minutes I had found a peer-reviewed scientific study that clearly showed that a variety of essential oils such as rosemary, thyme or oregano kill Late Blight spores on contact with tomato leaves - even in very low concentrations. I began spraying immediately last year, and noticed that it did seem to slow the spread of the disease significantly - but the plants were already too far gone. So it has been incredibly exciting to try it on healthy plants this year, and I couldn't be more pleased with the results.

Conveniently, this is a very affordable solution, since the mixture is diluted. Just mix 4 drops rosemary essential oil with 1 liter of water and spray your plants weekly starting August 1st. Here in the Northeast US, this is the time when tomato plants are beginning to reach the end of their life cycle (fruit/seed production) and are most vulnerable to fungal attack. I believe the reason my plants are so healthy this year is because I began spraying weekly as soon as I saw a leaf with Early Blight lesions - and there have been no other diseased leaves since. Planting herbs like basil between tomato plants doesn't just maximize space--it also means you'll be releasing volatile anti-fungal oils with each harvest!

Pruning. It is standard practice to prune the heck out of tomatoes (removing all suckers) and that is what I had always done until this year. After noticing how the black lesions seemed to climb the plants just as fast as I pruned, it occurred to me that with every cut, a wound is opened that allows any spores in the air direct access to the vascular system of the plant. Also, it seemed that since every branch that grew produced flowers and fruit, it made sense to let them grow naturally rather than pruning them off constantly. That being said, by late July the bottom 12" of leaves were starting to yellow and seemed a likely vector for disease (which is natural given that they are the oldest, first leaves the plant grew way back in April). So this year I tried something different - I didn't prune at all, except to remove the bottom 12" of leaves in late July. Since there is usually no sign of disease yet at this point, you don't have to worry about transferring spores from plant to plant - and by increasing air circulation in the part of the plant that tends to be splashed with water, you're avoiding another vector for disease altogether. At the very end of the season, you can force ripening of any remaining fruits by pruning off the tops of the plants.

Epsom Salts. There always seems to be a point in the season, usually in early or mid-August, when the tomatoes just seem to slow down. Hungry, tired and hot, they just want to quit and sit back with a margarita (sound familiar?!) If you look closely, you'll notice that they have no more flowers on them. If you do nothing at this point, they'll ripen any remaining fruit but the decline will continue into fall. If you water with Epsom salts, however, you'll get a whole new flush of flowers (more fruit), more sugar production (better flavor), and healthier foliage (less disease). Whenever my plants are looking a little tired (usually just once or twice in a season), I water with 1 Tablespoon of Epsom salts per gallon of water.

Tomatoes + beans trellised on CRW (PVC hoops support row cover)

Trellising. Years ago a friend introduced me to a method of trellising tomatoes that has completely transformed my tomato-growing experience. The method is to use sturdy, long-lasting panels of concrete reinforcing wire (CRW) attached with zipties to 6' cedar posts pounded into the ground. The tomatoes are planted between the posts (about 2' below the wire sheets), and are simply woven into the panels as they grow, creating a wall of tomatoes. The advantages are many, but the biggest are: cost (it's very cheap, about $12 to trellis 10 tomato plants), it improves the air circulation around the plants and maximizes space, the plants can put all their energy into fruit, and harvest is as easy as picking tomatoes off a store shelf. Best of all, the CRW sheets are readily available at any home improvement store, and are strong enough to last 20 years or more. If you prefer, you can also use hog or cattle fencing, which can be cut to size - just be sure that whatever you use is sturdy enough to hold the hundreds of pounds of tomatoes you can grow this way!

Soil + Containers. I always experiment with some container tomatoes, even when I have a garden full of them, in the hopes that I'll further extend the season on both ends. But almost inevitably, the plants in containers get stressed by lack of water or nutrients - and as a result they produce less and start their end-of-season decline earlier. The lesson? Tomatoes need good soil and plenty of water all the time in order to thrive. If you have to grow in containers, I suggest large 2-5 gallon self-watering containers that can be easily accessed for watering every morning. In raised beds, watering weekly will be required if it doesn't rain. And plants, like all creatures, need food - especially when they are young and growing quickly - so I topdress with organic compost around the plants at planting and again a month later, around July 1st.

I hope these tips will help you in your quest for healthy tomatoes. As always, I welcome your feedback, garden fantasies + botanical mysteries! **Comments are now open to the public :)

~ Sophia