How do you grow the perfect tomato?

Wednesday 4th May 2022, 12.30pm

Is there anything nicer than a fresh, juicy, home-grown tomato on a summer’s day? Whether you like them sliced up in a sandwich or blended into a delicious sauce, in this episode of the Big Questions podcast we reveal the secrets behind growing the perfect tomato. Let us transport you to Trap Grounds Allotments in Oxford, where Emily is joined by plant scientist Christian Norton, who is ready to reveal his five easy steps to the ultimate crop!

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Emily Elias: It’s that time of year again, the race is on to grow the most perfect tomato in the land, but how do you make sure yours isn’t going to fail? On this episode of the Oxford Sparks Big Questions podcast, we’ve got your gardening back and we’re asking, how do you grow the perfect tomato?

Hello, I’m Emily Elias. And this is the show where we seek out the brightest minds at the University of Oxford and we ask them the big questions. And for this one, we’ve decided to catch up with a researcher at the Trap Ground Allotments in Oxford who is ready to dig in.

Christian Norton: See, like, the apple blossoms are setting there. They’re coming out right now, which will be pollinated by, you know, spring pollinators, like the bees.

We can see the bees around now.

My name is Christian Norton and I’m a DPhil student in plant sciences at the University of Oxford.

Emily: Okay. So you are going to teach us in five easy, easy steps what do we need to do in order to grow the absolutely best tomato in the entire Thames Valley?

Christian: Those are some goals. (Laughter) I’ll do my best.

Emily: The first thing that I think people would probably need to start it off with would be a seed. So what do you think needs to go into consideration when you are picking your ideal tomato seed?

Christian: You can pick your tomatoes from seed or from transplants. And so in places with shorter growing seasons, it’s likely you would use a transplant, but obviously whenever you’re just picking a transplant or a seed, you have to pick the type of tomato you want, right?

And so you have to think if you want to do sauces or you’re thinking tomatoes for salad, maybe you’re drawing some tomatoes and also think of like what you look for in a tomato. Do you want something sweeter, something more acidic, more balanced? What colour tomato do you like?

There must be thousands of tomato varieties. And so the choice is yours.

Emily: How do we have thousands of different breeds?

Christian: Yeah. Well, tomatoes were likely domesticated thousands of years ago in South America. And since then, people are still breeding tomatoes now for qualities that you like, so you cross two tomatoes you like, and then you grow those seeds out and then based on the seedlings and their fruit, you grow those seeds long and pick the ones that have the qualities you like and those can be things like acidity, disease resistance, how fast they grow. It’s really the breeder’s choice. And so even now we’re developing particularly disease resistant tomato varieties.

Emily: Is that good for the species to have a lot of different varieties?

Christian: Yeah, of course. I mean good for the gardener as well. Especially when you’re breeding tomatoes that are more resistant to disease and we walked into this lovely garden. One of the gardeners commented that they lose their tomato crop to blight perhaps every third year.

And so if we can grow and breed tomatoes that have resisted to this you wouldn’t have that crop loss in your garden. So it’s really important.

Emily: Okay. So step one, picking the right plant, then I would assume the second most important factor once you’ve figured out what you want to grow is where you’re going to grow it, where you’re going to plant it.

So what do people need to consider when they’re planting tomatoes?

Christian: You need to pick a location with lots of sun. Tomatoes love sun. Like I said, they’re a plant that originated in South America. So you can imagine coming from that area, they would love a lot of sun and also spacing. And like I said, tomatoes are very susceptible to fungal diseases and so when it rains or you water them and if they’re quite cramped, they don’t dry well, and then that’s when you get diseases that will ruin your crop.

So lots of sun, lots of space and, again, talking about diseases especially within your garden, you should rotate where you plant your plants. If you’re growing tomatoes in container, which I’m assuming a lot of people will be doing, if you’re using fresh bag soil, that is fresh soil, so it’s not as important, but in a garden, you shouldn’t plant tomatoes where you had them last year, because when plants grow in a certain spot, that area builds up diseases that impact those plants.

So you should plant them in another part of your garden so that you don’t have those same diseases right next to plants as they start growing.

Emily: So if I grow tomatoes there one year, what should I grow in that spot the next year?

Christian: Things like potatoes, peppers, eggplant, they’re all related to tomatoes, they’re in the same plant family. And so it would be a bad idea to plant tomatoes where you had potatoes, peppers or eggplant. And so maybe peas or beans, carrots, something that’s not in that nightshade family that the tomatoes belong to so that you’re not building up these plant pathogens that are specific to those kinds of plants.

Emily: So what does it do when you plant beans in the spot, where you had originally planted tomatoes the previous year?

Christian: Yeah, so plants like peas and beans, legumes, they’re called nitrogen fixing plants. So they have little nodules in the roots where these nitrogen fixing bacteria live and they actually add nitrogen to the soil as they grow. And so that’s obviously really beneficial to other plants because nitrogen is one of the main nutrients that plants need to grow.

Emily: So I’ve got my plant. I’ve got the place in the garden that I’m going to plant it, how do I ensure that when it comes to time for the growing season of the tomato, that I get the maximum joy out of the tomato?

Christian: So you thought of sunlight and where you’re putting the plant. Now you need to think of water and nutrients, which are the other two main things that these plants need.

And so with things like tomatoes, You want to water them consistently because when tomatoes are allowed to dry out or get too wet, that’s when they start having disease problems like blossom end rot. So usually that’s caused by either too much fertiliser or a really poor watering schedule, like, letting them get too wet or too dry.

So the main things are consistent watering and also making sure the plants have enough to eat; they’re well fed, but not over fed, which causes problems. And so if you’re growing plants on a patio with, like I said, fresh bag soil, there’s likely enough nutrition in that fresh soil to feed your tomatoes for that growing season.

But in a garden, it might not be a bad idea to use compost, [unclear speech 0.06.22] and well-rotted manure, or even like a liquid like fertiliser application, like fish emulsion or kelp emulsion or something. It’s always great to ask, especially like this beautiful allotment we’re in, ask the gardens around you, what they do for their tomatoes, because they have grown them before and they know, kind of, what their nutrition needs would be in this area.

Emily: So it isn’t cheating by feeding them fertiliser and Miracle-Gro, sort of, stuff.

Christian: Very controversial. (Laughter) I mean, that’s something I just… plants need to eat. But if your soil is healthy enough, it’s unlikely you need to put huge amounts of fertiliser into the soil. I would suggest people are probably more likely to over fertilise their plants than they are to under fertilise them. And so it’s funny that often over fertilising looks like under fertilising the plants. You see like leaves yellowing, leaves browning, leaf dropping, fruit rot.

And so often you kill them with kindness or I suppose with tomatoes, they get too much new fertiliser, especially nitrogen, they don’t set much fruit. They just get really leafy and you don’t get many tomatoes. No, maybe a lighter hand with a fertiliser, especially in a home garden.

Emily: So they are grown away, let’s say it’s end- fast forward in time. It’s now the end of summer. Another key thing to factor in would be harvesting. So what is your advice? When do you harvest the perfect tomato?

Christian: Whenever it’s ripe at. (Laughter) Whenever that tomato is at its- obviously when you bought the tomato, it came with some kind of seed packet that described what the mature fruit looked like. And so if it’s a red tomato, you pick it when it’s at its most sumptuous, delicious red.

Some of them don’t turn totally red. Some of the heirloom varieties stay, kind of, a maroon and, kind of, stripy. But based on the tomato you picked that would give you information on when to pick it. Something I didn’t mention, in the picking process of tomatoes is that they come into, kind of, two main groups.

You have your bush tomatoes and you have your vine tomatoes. And so your bush tomatoes are called determinant tomatoes, and they, kind of, grow to a shorter height and then they set all their fruit at once. And so you get a huge crop tomatoes at the end. And so if you’re making sauces or, you know, canning or jarring tomatoes that would be the variety you would want.

But if you want tomatoes, kind of, over a longer time period, you want tomato sandwiches over the summer, you might pick a vining tomato that sets fruit as it goes and ripens them along. So you don’t get a huge, you know, crop tomatoes at once. You, kind of, get them spaced out along, but the vining tomatoes take more space than the bush tomatoes.

So that’s something to think about when it comes to the harvest based on the type of tomato you planted.

Emily: So you would think that once I picked my tomatoes, like, job’s done, but at the end of the season, the job isn’t quite done yet. What is the most important final step in growing the perfect tomato?

Christian: The job’s never done in gardening. And so tomatoes in their natural environment in South America are a short-lived perennial, meaning that they come back for a couple years. They persist over time and have multiple, you know, crops of fruit, but in our colder environment, like the UK, North America, you know, USA, Canada; tomatoes are an annual, so they only grow for one season and they die when it gets cold.

And so it’s really important in gardening that once you’re done with these plants, you remove them from the garden and you dispose of those plant materials, because like we mentioned before about diseases, when you leave leaves and stems and bits of fruit and all that where the tomatoes were, that causes certain diseases to build up, which will then impact your tomatoes of next year.

There’s two tomato fungal diseases that over winter in soil and leaf and plant debris. And so you don’t want to leave that stuff just rotting in the garden. I mean, you would think, you know, it would just be compost for the soil, but you’re more likely to harm your garden in the long run by leaving those disease containing materials there.

Emily: Really?

Christian: Yeah.

Emily: I didn’t know that. I just thought if I just left it, it’ll be fine until next spring when I want to start again with my tomato crop.

Christian: No, you’d think, but like I mentioned, plants when they grow in a garden or in a pot or whatever what tends to happen is there is an increase of pathogens in that area that like to eat that plant, which makes sense, right?

So things that like to eat that plant show up in that area. And then if you don’t remove that food source or what’s supporting those pathogens, they stay there. And then whenever you put the plants in next year, instead of these pathogens coming in later, they’re there from the get go and so those seedlings are being attacked or eaten right away by these fungal diseases.

Emily: So you’re not even having a good start. You’re giving your tomato a disadvantage from the offset, and you’re never going to get the perfect tomato that way, are you?

Christian: No, you won’t. Exactly. If you’re investing time and your money in this, you want to give these tomato plants the best possible start.

Emily: Well, okay. This is incredible. So if I follow these five steps on picking the seed, planting, growing, harvesting, and then cleaning up after my mess, do you guarantee that I will have the perfect tomato?

Christian: I guarantee any tomato you grew yourself that you then made into a delicious tomato sandwich or nice salad, you would in your heart know that is the perfect tomato.

Emily: That’s the perfect answer.



This podcast was brought to you by Oxford Sparks from the University of Oxford, with music by John Lyons and a very special thank you to Christian Norton.

Tell us what you think about this podcast. We are on the internet @OxfordSparks. I’ve said that once, and I’ll say it again @OxfordSparks. We’ve also got a website, We’d love to hear from you.

I’m Emily Elias, bye for now.

Emily: Back into our tips. So we’ve got plants, we’ve got a place that we want to grow them. How do we make sure that we grow really big and – oh my God, I’m getting eaten by ants.

Are we sitting on an ant mound?

Christian: We might have.

Emily: Oh.

Christian: There’s just a few. We’ll just go…



Transcribed by UK Transcription.