I hear a lot of people say well intentioned but not always accurate things about tomatoes, and it’s time to set the record straight.
Disease Resistance
It’s true some (not all) modern tomato varieties have some special disease resistance. The most important diseases are Fusarium and Verticillium wilts. These are different but similar diseases, with nearly identical symptoms, and depending on your climate you may have one or the other in your soil but probably not both. If your plants get this the leaves will become seriously wilted, and while they may still produce some tomatoes the harvest will be much lower than usual. This is soil borne, so you may have it in one part of your garden but not another. It’s not very contagious so if a plant gets it you may as well let it grow and see what happens.
While these wilt diseases are common, most gardeners probably won’t have them in their gardens in which case they are simply not an issue. It’s not worth losing sleep over this until you know for sure you have this problem! If a wilt disease is present in your soil, there is little else you can do except grow resistant tomato varieties or grow your plants in pots with known disease free soil like purchased potting soil, home made compost or a mix of the two.
It’s worth mentioning some heirloom varieties may have some resistance to these wilt diseases, no one really knows because there hasn’t been much research done on this.
For the home gardener, modern tomatoes don’t have any other important disease resistance!
The other disease resistance in modern tomatoes is only important to farmers. For example the tobacco mosaic virus generally only occurs in greenhouses, but because it is common in tobacco plants if you do smoke you should be sure to keep your tobacco away from your tomato plants and wash your hands before gardening.
Heirloom tomatoes have disease resistance too! For most other plant diseases, some resistance can be found in a few heirloom tomato varieties. For example common tomato and potato diseases are early and late blight, and while no tomato has complete resistance to these, some currant tomatoes have shown a little resistance. No commercial varieties have any resistance to these two blights.
It all depends on what diseases you have in your garden, and it’s important to understand this before coming to the conclusion that choosing either commercial or heirloom varieties is the answer.
It’s Not Necessarily True Hybrids Are More Productive
There is often the assertion, usually by seed companies trying to sell more seeds, that hybrid varieties are more productive. This is a very disputed assertion! The basic idea is that if you have a highly inbreed plant variety, it can show signs of inbreeding depression which can result in lower yields. Since creating a hybrid variety is essentially the opposite of inbreeding, it must result in higher yields.
The flaw in this logic is that tomatoes are naturally inbreeding plants, and don’t usually have problems with inbreeding depression.
It’s not that productivity gains are not possible in hybrids, but it’s not always true and many heirloom varieties can be as productive as hybrids.
It’s Not Always True Heirloom Tomatoes Taste Better Than Hybrids
Commercial varieties are almost always breed for supermarket cosmetics, growing and transportation convenience and low cost of production. Taste is not usually a factor when they are developed.
If you compare a heirloom tomato to a commercial variety under these circumstances, it’s certain to taste better.
You can make your own hybrids! By choosing two of your favorite heirloom tomatoes and cross-pollinating them, you can easily end up with a tomato that tastes better than any pure breed OP or heirloom variety.
The parent varieties of commercial varieties are generally kept secret, so it’s not possible to experiment with or improve on these. If you make your own hybrids you can collaborate with other gardeners and work together on finding great combinations.
There Are Problems With Heirloom Varieties
All food plant varieties need to be periodically ‘grown out’. This means a large number of plants, sometimes numbering in the hundreds, are grown out and selected for desirable traits. Plants with undesirable traits are rogued out or removed, and seeds are saved from plants with desirable traits. When this isn’t done, the genetics of a particular variety will deteriorate slowly over time and develop undesirable traits leading to problems like susceptibility to diseases or pests, loss of productivity and loss of quality.
Growing out plant varieties takes time and money. Some home or hobby gardeners do large scale grow outs, but this involves only a small percentage of heirloom varieties. Commercial varieties simply have the money and support of large companies behind them who can afford to grow them out more often and maintain them better.
Many heirloom varieties are in a very bad state in this way! This is not just tomatoes but all different kinds of fruits and vegetables.
Also, because many heirloom varieties were developed in a single person’s garden or in a single region they have become ‘landraces’, that is well suited for that particular region. If you try to grow a variety like this in a different region, it likely won’t perform as well.
There is Something You Can Do About This
It may not be possible for you to grow hundreds of plants in your garden and do a full scale grow out of a particular variety, but you can do this yourself on a smaller scale.
If for example you are able to grow in the neighborhood of 10-50 plants of the same tomato variety, only save seeds from the best ones and hopefully do this for a few years in a row, you will likely end up with a significantly improved variety which has also been acclimated specifically to your garden.
Other Things You Can Do To Improve Your Chances
Talk to other gardeners and find out what’s done well for them. In particular if a nearby gardener has found something that does well in your climate, consider getting some seeds from them and growing it too.
Not all seeds are equal. If something didn’t do well for you, but did well for someone else who got the seeds from somewhere else, consider getting some of the same seeds and trying again. I know the Seed Savers Exchange is doing grow outs of many of their varieties, and I imagine other seed companies are by now too. Consider that improved seeds may soon become available for popular varieties.
I have to share that cartoon with my fiance–it cracked me up because it fit him so well.
This is great information. In small plots, like mine, I think it is impossible to grow many multiples of tomato varieties, but I can do the “grow-out” process on peas and a couple other crops. Thanks for pointing out the need to do this.
Have a great weekend!
Oh boy, that is exactly how I get into trouble at night! My husband will love that cartoon.
Great post – I’m glad you addressed disease resistance. There is so much emphasis on that aspect lately, it drives me batty.
I like these strange coincidences. I put up a post myself today suggesting that people try making their own tomato hybrids.
This is all nice and clearly put, Patrick and obviously tomato questions are the same the world over!
As for insect attack on tomatoes, we have a new and nasty infestation of mites, invisible to the naked eye, that are devestating tomatoes in Adelaide in the last 2 years. Although my garden rarely has any pest problems because of my work with nature, not against it, approach, these mites ruined all my tomato plants this year.
Thanks for the comments everyone.
Melinda: Keep in mind that while disease might not be as important as everyone says it is, because of the problems I did mention here, it can seem like your plants are diseased and you should have tempered expectations the first year you grow any unknown heirloom variety.
Kate: The problem we have here in Holland is blight, usually late blight. There are a lot of commercial potato farms which host the disease, and it’s just everywhere. The solution usually is to grow the plants somewhere where the foliage stays dry like a greenhouse, and while this doesn’t prevent infection it keeps it from spreading too quickly. Invisible mites sound very frustrating.
Great post Patrick! As you know, I am very interested in heirloom tomatoes. I am also pretty new at growing them. I’m pretty sure that much of what you are disputing came from my writings. I just put up a new post talking about that and about this post that you have written.
I also have a dumb question. If you want to save the seed of an heirloom, and you do not want to try to create a new hybrid, how can you be sure that it hasn’t cross-pollinated with another variety? I have read that you should grow different varieties apart from one another, but how far? And unless you only grow one kind of tomato, how can you be sure that it hasn’t crossed?
Thanks for the great post as usual.
Ah! Another xkcd fan… 😉
Chillis are quite prone to Tobacco Mosaic Virus, so should be kept a reasonable distance from Tomatoes, too. I had a hell of a time some years back when a number of the Jalapenos got TMV, and I lost a significant proportion of the crop. In truth, it may have been some other virus — Capsicums are notoriously susceptible to quite a bewildering array of viruses, many carried by Tobacco — but TMV remains the Prime Suspect. I’d had a labourer working in the garden who smoked… :-O
With all this talk of hybrids and genetics, maybe we should start an Heirloom Tomacco Project 😉
Well put post. I can hear my DW sighing when I tell her I am growing 20 or so tomato plants of one kind to select the better plant.
Marc: Thanks for the comment and post! They were both really nice.
To answer your question about tomato seed saving, it depends on how pure you want your seeds to be and how much trouble you want to go through to try to isolate them.
Generally speaking it’s not much of an issue with tomatoes, because they are mostly inbreeding plants and don’t tend to cross much. It’s very rare when the rate of accidental crossing is higher than 5% in home saved tomato seeds, even under the worst of circumstances.
For some people the occasional cross is a good thing, it can be interesting to see what you get. Also, if you are looking out for it, you can often notice crossed plants when they are pretty young and just remove them if you don’t want them.
If a 5% rate of crossing is too high for you, you can reduce this by putting some space between the plants. A couple of yards will make a big difference. Since they are usually crossed by insects, you can also cover your plants with fleece row covers to keep the insects off. Since commercial seed companies really have to make sure they sell very pure seeds, they may separate the plants by some tens of yards and/or use fleece covers.
The one thing you should be careful with is currant (sometimes called wild) tomatoes. These will much more easily cross with themselves and regular tomatoes. You should not grow these in the same part of the garden you are saving tomato seeds from, or cover them with fleece.
Mike: Thanks for the info on the TMV! I didn’t know it was much of an outdoor virus. Perhaps more or less the same thing applies as with the wilt diseases, that it’s not so important to lose sleep over it until you know it’s a problem in your garden. I have the sense the TMV is not that common when all is said and done, but maybe I’m wrong…
Yes, I wonder if we can develop a plant where you can both smoke the leaves and eat the fruit. That would be an accomplishment!
Curtis: Thanks for stopping by!
Love the cartoon and I think I am going to forward this link to anyone who has been infected by this virulant form of advertising that sends people away from heritage tomatoes.
On that note, I second the need to trial a new heirloom. I was excited about Pontimarron squash but in my garden it produced later than expected and drew the cucumber beetles like chocolate draws me (I like chocolate). This is not to say that it won’t do wonderfully well in other gardens and it is an heirloom in decline so perhaps could use a grow out.
Oh to do a grow out. Why I need to purchase some land.
Thanks again for another well thought out, well written post.
Hello. This is my first year gardening and I have about 9 tomato plants. 4 cherry tomatoes, a few beef steak, a cheroke purple, an early girl and a mr yellow stipy I think. Anyway, the only plant I seem to be having problem with is my yellow stripy. It is a gorgeous plant and my favorite one.. However I am notice a wierd flat brownish sun scald like on the bottoms only. Is this blight that you were refering to earlier? Or could it be that it is sun scald? I do live in the desert and sometimes it can get 110. Please help!
Hi Sarai,
I think the problem you’re having is blossom end rot (BER):
http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Tomatoes/Tom_BlossRot/Tom_BlossRot1.htm
If you are growing your tomatoes in a container, it’s probably because the container is too small. Otherwise it’s usually a problem with not getting enough water.
The root of the problem is the tomatoes are not getting enough calcium, and while it’s possible there’s not enough calcium in the ground, this isn’t usually the true cause. Most of the time it’s a problem of the plants not getting enough water and so can’t absorb enough calcium from the ground.
If you think there might be a shortage of calcium in the ground you could add a small amount of lime or some crushed egg shells.
If you have staked your tomatoes, it’s possible you have tied it to the stake too tightly and it’s getting pinched off. This can cause BER. This happened to me one year.
Otherwise, if you don’t think any of these could be causing the problem, you just need to have a look around and see if you can find anything that might be keeping the tomatoes from getting enough calcium.
Good Luck!
Hello,
I just wanted to say thank you for all the help. Sadly I have another problem.. I have been trying to grow my garden as organic as possible and I have these little sugar ants climbing up my tomato cages and eating my tomatoes! They eating everything, watermelon, cantelope, bell peppers, even my jalepenos! I tried , instant grits, cornmeal, tabasaco, cloves, cinnamon, garlic oil.. So far they always come back. This old man at the extention office here in the tri-cities told me that nicotine is a natural insectacide, but I also heard that the tabacco virus can kill your tomato crop… Please help!
Hi Sarai,
While natural, nicotine is also very toxic. It’s just as toxic for your garden as it is for people. Like you said it can also have the tobacco mosaic virus.
Ants don’t normally eat plants, so perhaps it’s worth looking carefully at the situation and try to figure out if the ants really are a problem? I have ants in my garden, and while annoying they aren’t really a serious problem. I just let them be.
If you decide you really have to do something about the ants, I suggest scalding hot water. This can kill plants too, so you need to be careful where you pour it. You should look for the ants nest if possible, or the areas where most of the ants are. Don’t expect to kill all the ants in one go, just try a kettle full here and there for a few weeks and see how it goes, then use more water if it seems to be working.
You probably won’t kill all the ants with hot water, but rather disrupt the nests enough so they move on someplace else.