The Science Of Your Summer Vegetable Garden

[MUSIC PLAYING] (Singing) Inch by inch, row by row, going to make this garden grow. All it takes is a rake and a hoe and a piece of fertile ground.

IRA FLATOW: Years ago there was an old radio program on WOR in New York called “The Garden Hotline.” it was hosted by horticultural expert, the late Ralph Snodsmith. He always started his show with that John Denver music you’re listening to. I listened to that show every Sunday morning as he fielded gardening questions from listeners.

Questions like, can coffee and tea grounds help acidify my soil? Well, not to any marked degree is the answer. Question, can seedlings thinned from a row of lettuce be used as transplants? Answer, if you’re careful with their tiny roots, yes. Question, is it better to plant my tomatoes on a sunny or a cloudy day? Answer, cloudy, since reduced light exposure reduces transpiration.

As a backyard gardener myself, I still have lots of questions. And I know so do you. So we’re recreating that garden hotline, hopefully giving you some science behind the gardening tips. We’ve collected your science-ee gardening questions, and we’ve asked two guest experts to answer them. Here they are.

Elizabeth Buck, fresh market vegetable production specialist with Cornell Cooperative Extension, which is in Ithaca, New York. Gary Pilarchik, author of The Modern Homestead Garden and host of the “Rusted Garden” YouTube channel. He lives in Howard County, Maryland. Welcome, both of you, to Science Friday.

GARY PILARCHIK: Thanks for having me.

ELIZABETH BUCK: It’s great to be here. Thank you.

IRA FLATOW: And just a note to those listening. We’re recording this segment in front of a live Zoom audience. And if you would like to be part of our next Zoom audience, you can find out more about attending future segments at sciencefriday.com/livestream.

OK, let’s get right to our questions. Gary, let me first say that I really enjoy your “Rusted Garden” videos on YouTube. I’ve learned a lot. I hope you can share some of your down to earth knowledge with our listeners. So let’s get right into it.

Our first question, submitted via the Sci-Fri VoxPop app. And this is from Dan in Yorkville, New York.

AUDIENCE: I’d really like to hear about some nice nonlethal means of keeping squirrels, and rabbits, and whatnot from getting to tomatoes and things like that. Also, I’d like to see if there’s some nice non-lethal, non-toxic way of keeping insects out of the garden as well.

GARY PILARCHIK: Well, you try reasoning and they just don’t stay on one plant. So they do become a nuisance. And they will take everything down. Nonlethal way, I have so many squirrels where I’m at on my two acres, I had to do trap and release and move them five miles away. Some people may not want to do that, but it can be done. You have to move them away.

The other thing is because squirrels are such big climbers, even if you use a fence or you create something high, they will just climb over it. Fences are great for groundhogs and other things like that.

But it’s really, really a challenge with even birds, small animals, and such. There are sprays you can put out, but they tend not to work for squirrels. And a good rain comes, it washes them away. You can try planting stuff away from your garden. Maybe they’ll eat that, and get their fill, and not come over to your garden. But it’s really, really difficult.

And nonlethal ways for insects and maybe like diseases and stuff like that, at least for insects, any kind of organic dust or insect dust that you use, even though it’s organic and safer for you and me, it’s going to kill good and bad insects. So you have to be aware of that too. So it’s really hard not to harm your pollinators or your bees.

IRA FLATOW: Elizabeth, I know that pollinators are very important to have in your garden, are they not?

ELIZABETH BUCK: Yes, absolutely. And pollinators are good for all of your plants, but not all of them need them. One of the cool things is that a lot of plants are self-pollinating. And those are things that tend to have closed flowers. So your tomatoes, for example, they tend to pollinate themselves. So if you’re not seeing a lot of bees on your tomatoes, no worries, that’s fine.

I think the coolest thing about pollinators is that it’s not just bees. There are native bees, there’s flies, there’s insects. All sorts of critters are out there doing the work of pollination. So it’s really this great biodiverse system out in your Garden

IRA FLATOW: And I know, Gary, that some people choose to grow their veggies in a container. I’ve seen on your YouTube you showing us how to do that. Will that keep some of these pests away, if you can grow them in a container?

GARY PILARCHIK: I wish I could say yes it does that. Each gardening zone is very unique. So whatever pest you have or whatever critters you have, they can find your way into containers and stuff like that. If you have a really big problem, one container I have, it’s just a big fire ring that you would buy. I’m growing a Brussel sprout in there. And I’ve set up a couple arches and put ag fabric over it. And it zips shut. That is the way to keep out squirrels, birds, and stuff like that. But you have to make a decision on do you want these big ag fabric tents everywhere.

Let’s go to Ryan, who has a question about their garden onions. Ryan, you’re growing onions. Go ahead.

AUDIENCE: Yeah, so I grew some onions that I got from the garden store, the little shoot starts, not the bulbs. And I thought they would not go to seed, but they did go to seed. And I didn’t know if that was because it was– we got a COVID period after I planted them. So maybe they thought they went through winter. So I was just A, looking for an explanation on that, and B, wondering if I could gather the seeds from them to plant for next year, and how I go about doing that. They’ve developed the seed head and they just started opening up.

IRA FLATOW: Gary, what do you say to help out Ryan there?

GARY PILARCHIK: Yes, starting– you can collect the seeds and you can use them. And sometimes onions do better if the seeds are put in directly. And you kind of answered the question. Onions are biennials, so even if they’re small and they bulb, and they think they’re on their second year growth sometimes they more quickly go to flower. It could have been that cold period.

Could be– sometimes– and I’m not 100% sure, but you got short day, midday, long day onions, sometimes that can impact them too, based on where you’re growing. When we buy those onion bunches, we don’t always know what exactly those onion varieties are except they’re yellow, white or red. There’s not a lot of information there.

IRA FLATOW: This is Science Friday from WNYC Studios. OK, let’s go to Elizabeth. The Question. For you from Ariel from Pittsburgh. It seems like plants choose between lush leaves and abundant fruits. Some of my best performing tomato and pumpkin plants are a bit spindly, while those that are super green and lush have lower yields. Why is that? And how do I get them to make more fruit and less leaves? Any ideas?

AUDIENCE: Yeah, that’s a great question, Ariel. And it all comes back to how the plant balances energy within itself. So plants will do a lot of vegetative growth. And that’s the big green happy leaves, or they do reproductive growth. And because they’re vegetables, they’re relatively short-lived plants, once they make the switch to reproductive, to fruiting, they don’t easily want to go back and push a lot of that green tissue out.

So sometimes we can love our plants a little bit too much. And if we over-fertilize them, particularly if we give them too much nitrogen, the plant responds to the nitrogen by growing a lot of leaves. And life is good, and life is easy, and it grows a lot of leaves and doesn’t get to fruiting.

The other thing that can happen is that when plants are really stressed it pushes them towards growing fruiting more because they’re a little bit worried they’re not going to make it through. So in that case, when your plants are a little bit spindly sometimes they’re going to produce more because they’re kind of worried.

So you can balance things out in your garden and get a good sized plant that still puts out a lot of fruit by adjusting the amount of nitrogen and potassium that you feed your plant. Because most vegetables when they’re putting out fruit they need less nitrogen and more potassium. So you want to kind of change how you feed your plant.

IRA FLATOW: Gary, what kind of fertilizer do you feed your plants?

GARY PILARCHIK: I focus on two things. If I’m doing a granular fertilizer, any organic granular fertilizer around the 5-5-5 at N-P-K, that’s pretty balanced. Up or down a few numbers is fine. That’s a slow release, which means when you mix it into your soil, it takes some time for the microbiology to break it down. And it slowly feeds your plant, say, over a couple of months.

Then you have your water soluble fertilizer. What I use for that is fish emulsion. It’s a 5-1-1 N-P-K, more of the nitrogen, as Elizabeth for saying, that helps that green growth get started. And being water soluble it means it’s immediately available to your plant. It can use it right away.

So in combination, it’s good to have organic granular, your water soluble. But in addition to that, I put my beds to rest in the fall with compost, with leaves, I even put wood ash on them, even alfalfa pellets, to just kind of put organic matter in there. And I do the same thing again in the spring.

ELIZABETH BUCK: I think you’re got a really strong point there, Gary, when you say it takes time for the organic fertilizers to break down. That’s, I think, where it’s hard for people to gauge how long. And so it’s good to think of your garden in terms of what’s the slow release fertilizer and what’s my quick release fertilizer. And if you can do that, then you can set yourself up for a lot of success.

IRA FLATOW: We’re going to take a break and when we come back more of the science of your summer vegetable garden. Stay with us.

This is Science Friday. I’m Ira Flatow. In case you’re just joining us, we’re talking about the science of your summer vegetable garden with my guests Elizabeth Buck, fresh market vegetable production specialist with Cornell Cooperative Extension, and Gary Pilarchik, author of the book The Modern Homestead Garden and host of the “Rusted Garden” YouTube channel.

All right, let’s go to back to our audience. Mary– Mary has a question about basil. I love my basil. I’m waiting to hear what Mary has to say. Mary, go ahead.

AUDIENCE: Well I am a basil failure. I have planted probably I don’t know how many seed packets of basil. And last year, I went through three of them before it finally dawned on me they may like it really hot, like zinnias have to have really hot sustained weather to germinate. This year I waited until it was just murderously hot. And I planted multiple times and I haven’t seen a single seedling. I don’t get what the difference is.

IRA FLATOW: Elizabeth, you’re shaking– you’re nodding your head in agreement here.

ELIZABETH BUCK: So are you planting it into a container or right out into the soil?

IRA FLATOW: Mary?

AUDIENCE: Soil, in soil.

ELIZABETH BUCK: So basil– you’re right, basil does want to Germany under warmer conditions. And it’s a little tough sometimes when you do it right in the soil. Lots of times there’s better success in starting the basil inside in that small pot and then transplanting it outside. And that’s because there are a couple of diseases that will take out the seedling just as its germinating.

And so it’s sometimes more successful to just take that element of uncertainty out of the picture and start inside. And that way you can control the moisture levels too. Basil doesn’t really like heavy clay soils. So if you’ve got a heavier soil and your brother, your neighbor, whomever has a lighter soil, they’re going to be a little bit more successful getting it to germinate directly in the ground.

IRA FLATOW: Gary, any hints from you?

GARY PILARCHIK: I agree with that. So getting a basic potting mix or starting mix and just like a little yogurt container, and when it’s warm, the basil is looking for warm soil, warm ambient temperature. If you plant it up in a little container and you keep it outside, just let the top dry. That’s when you know to water again. But let that top dry. And that helps with that damping off kind of disease that comes along. And that’s how I start all of mine. And they do transfer nicely into the garden that way.

IRA FLATOW: How do you know when it’s better to go to the garden store and buy a little basil plant rather than starting from seed? And I guess generally for all of your plants, Gary?

GARY PILARCHIK: So I have a thing against buying plants from the big box stores. Go to your local nurseries, know the people that are growing the plants. Sometimes you can buy basil that’s been sitting, it’s not been watered. It struggles, it’s getting tall, it doesn’t look great. It looks great, but it’s a little bit past its prime. By the time you get it to your garden, it wants to go in flower really quickly.

So I do recommend either getting really small transplants from your local nursery and getting them into your soil or going by seed. Just be careful that you’re not buying plants that have been totally stressed at your local big box stores because it damages the plant. And like Elizabeth was saying, sometimes when they’re stressed, then they go right to fruit production, trying to reproduce. And you just have a hard time getting them going.

IRA FLATOW: Let’s go to another Zoom call. Carol– Carol has a question about her compost pile. A gardener in our family puts a lot of coffee grounds, bags and bags from a coffee chain into the compost pile. How much is too much? Elizabeth, can you field that one?

ELIZABETH BUCK: Sure. So when you’re mixing compost you want to balance everything out. And so you have to think about what are the characteristics of what I’m putting in. So if you’re putting in a lot of coffee grounds, that’s going to be a acidic material. It’s going to be a fine texture material. And it’s going to be a material that’s maybe not the fastest to break down compared to some other things.

So it becomes more of a question of volume. Can I balance out this volume of coffee grounds with an equal volume of something that’s going to be very complementary to it. And really, I think that’s more a question of how much space do you have in your composting area.

IRA FLATOW: Do coffee grounds acidify? They’re sort of acidic by nature. Do they acidify the soil? Can you plant them or spread them on the ground to make it more acid, Gary.

GARY PILARCHIK: I think the answer is in theory it sounds good, but you would need a lot of it. So what you’d be putting down– if you’re just sprinkling grounds down anyway, they need to be– they need to break down by the soil microbiology. And sometimes that kind of moderates things a little bit.

If you needed something to quickly change the pH of your soil, you’re better off using something else. I wouldn’t mix a lot of coffee grounds into your container mixes. But you would have to use a lot.

IRA FLATOW: And while I have you here, and I watched your video on this, because this is the first year that I am planting potatoes. I, mean I’ve tried the potatoes in my five gallon bucket. I’ve got one in one of these cloth buckets. And they’ve been growing terrific. They grow giant stalks. And then they have flowers, gorgeous flowers. Who knew that potatoes had such gorgeous flowers on the top? How do I know when to dig them up, Gary?

GARY PILARCHIK: After they’ve been growing about 70 days, there’s probably potatoes in there. You can kind of dig around and pull some out if you want to. But you really know when to harvest them when the greenery starts looking yellow. You’re going to think it’s sickly. You’re going to start to worry. You might want to start feeding it more. That’s just the natural end to the potato.

So when it starts to yellow, turns brown, you know, dies off, you can let them sit-in there a week or so and then you can harvest your potatoes that way. That’s the sign they’re ready to go. And when you do harvest them, a lot of people don’t know that you can plant potatoes again, especially the early 70, 90 day potatoes. So when you’re harvesting, start some more. And you can take them really through the summer.

Sometimes it gets too hot. But I recommend people keep a journal. I always say try it, experiment, take notes. If it doesn’t work, it doesn’t work. But you can continue potatoes all the way into the frost period in your area.

IRA FLATOW: Well, speaking of hot, Elizabeth, we’ve had a lot of questions about the heat this summer, 90s, 100s, triple digits. What’s the best thing you should do to protect your garden from all of this heat?

ELIZABETH BUCK: That’s a great question. And we’re going to continue to see more heat as we move forward in time. Plants are built in to cool themselves. And the way that works in a plant is it draws water up through the roots and lets it out through the leaves, it’s evapotranspiration. And it gives us a really good way to check on how our plants are doing.

If you walk up to your plant and you grab a leaf, in the middle, not one right up on the top where it’s in the sun, but one in the middle, that leaf should feel cool to the touch. And that means the plant is happy and has got enough water moving through it to keep itself cool. Because they have this built-in mechanism, it really comes down to, can I give my plant enough water?

So the other thing you can do is kind of redesign your garden. And say, all right, maybe this plant doesn’t need to be in the sun for 10 hours a day. Maybe it only needs to be in the sun for six hours a day to grow properly. And by taking it out of the sun those extra hours, planting it in a different place, reducing the amount of stress and the amount of water it’s going to consume, which lets it cool itself better.

IRA FLATOW: Great answer. That’s something– we all can use that advice. Let’s move on to a Twitter question. Sylvia Wright from California asks us, what’s the truth about blossom end rot in tomatoes? Let me begin with that, Gary. How do you stop that?

GARY PILARCHIK: So the truth, she’s probably talking about you hear two things. There’s not enough calcium, add calcium, or it’s just a watering issue. And it’s really kind of a combination of both. If you’re not watering your tomato plant properly, the roots can be affected and you may have calcium present. And you can’t pull that calcium into the plant system. So it’s not really a calcium issue.

However, if you put some calcium nitrate, some calcium that can be pulled in through the leaves or more easily absorbed, that can help out the problem. The best thing to do is just have some lime in your soil, know that the calcium is there, and stick with that consistent watering. This happens a lot more I think with the Roma type tomatoes and with containers.

If a container– because of the heat that we’re talking about, you may have to water a container plant twice in a day. So moisture, keeping it consistent, mulching out in the garden, and knowing that you have calcium present. You don’t need a lot of calcium. Watering, I think, is the bigger issue.

IRA FLATOW: Elizabeth what does blossom end rot look like, for people who don’t know what we’re talking about?

ELIZABETH BUCK: Absolutely. So blossom end rot is on the bottom of the tomato. And the reason it’s on the bottom of the tomato is, remember those straws that pull the water through? Well, the bottom of the tomato doesn’t have very many of those straws. And if it doesn’t have a lot of straws it can’t pull water.

Since calcium moves with the water in the plant, no water goes to the bottom of the tomato, no calcium does to the bottom of the tomato, and the cells at the bottom of the tomato, they can’t expand. Calcium is really important in allowing plant cells to grow, and divide, and get bigger. And when they can expand, they die.

So what ends up happening is you get this brown or dark gray dead spot on the bottom of the tomato. And it starts out is a firm rot. Sometimes a secondary rot will come in. But it’s a firm, dry, brown or dark-colored rot at the bottom the fruit. And it’s really characteristic.

And the important thing to know about blossom end rot is exactly what Gary was saying. It’s about making sure that your watering is consistent. And the second thing to know about diagnosing it is the problem that you see probably happened two to three weeks ago, that the plant was deficient in water and/or calcium.

GARY PILARCHIK: Yeah, that’s a good point too. Because people say can I save my tomato that’s brown on the bottom. If it ripens, you can actually cut it off. But those are pretty much goners. But you can start watering consistently and getting it back in shape. And then the future tomatoes will do OK.

IRA FLATOW: OK, great advice so far. Let’s go on to the next question on Facebook. Scott Klaus wants to know why is my cantaloupe not growing? I planted them as starts at the same time as my zucchini, when they were the same size. Now my zucchini are much bigger. Elizabeth, what advice do you have?

ELIZABETH BUCK: This is a lot of back and forth troubleshooting. And sometimes it’s not easy to do this. There are resources for home gardeners to use and great books. What’s Wrong With My Vegetable Garden is a good one. And the reason I’m saying that is because without being asked the question live, I can’t really answer. But I can take some guesses.

And the first guess is that these are plants that are in the same family. So they oftentimes have very similar needs. So that means that it wasn’t planted at the wrong time, it’s not getting too much or too little water, compared to the one next door, the zucchini. So in those situations I am oftentimes wondering was the cantaloupe maybe struggling with something when it went into the ground? Was that transplant maybe having a little bit of root rot before it was ever put in the ground?

And that’s something that can come from a greenhouse center. It’s really common. But it’s good to know and be able to check out your plants ahead time. Because then you end up in situations where you get a big zucchini and a sad cantaloupe.

IRA FLATOW: Anything to add, Gary, to that?

GARY PILARCHIK: I agree with that. Because that goes to sometimes you’ll buy the cantaloupe and maybe it dried out or wasn’t treated well. Some things that you can do with that cantaloupe is you can give it that fish emulsion and you can try and give it more nitrogen. And you should see it start to green up over three to five days. You can do it again. And just see if you can save the plant.

If you’ve given it a couple of weeks, it doesn’t look good, that’s when I recommend replanting new seeds or maybe start some back-up plants when you notice it’s struggling. So that when you decide to pull that out, you can put in a new cantaloupe and maybe that takes off. And this way, you don’t lose much time.

IRA FLATOW: Good advice from both of you. This is Science Friday from WNYC Studios. Let’s move on to Daniella on Zoom. Daniella has a question about cucumbers in her garden. Daniella, what’s your problem?

AUDIENCE: OK, the problem is that I got these beetles. They’re striped. And I think that they are cucumber beetles. And I really want to get rid of them because they are also attacking my pepper plants. And they leave holes.

IRA FLATOW: Elizabeth, what do you suggest?

ELIZABETH BUCK: So cucumber beetles are a very pesky, annoying insect. And I think the best tool for a cucumber beetle is exclusion. So Gary earlier mentioned ag fabric. There’s a very lightweight spun woven material called row cover. And row cover is– it does exactly what it sounds like. You put it over top of your plants. And you put it out when you plant. And keep that row cover on them, with a little bit of give. It lets water through. It lets sunlight through. It lets air through. But it keeps the cucumber beetles out.

When they start flowering, you want to take the row cover off because cucumbers do need pollination. And at that point in time if the cucumber beetles move in, then from a homeowner standpoint you can try to repel them. They don’t like gritty feeling things. So there’s kaolin clay based products that will repel the cucumbers away from your plants. And that’s organic.

And if you really feel like you want to try spray them, you can try to use something called Pyganic. It’s another organic spray. And it’s a little bit more effective than [INAUDIBLE].

Gary, you mentioned that your gardening. I know you’re in Maryland. So that would be zone 7. Explain to people what the zone system is all about.

GARY PILARCHIK: So I think North America is the only place that uses the zone system. And because of how we feel about weather changing, the zones are changing. So they’re a little bit outdated. But they were kind of set up to help you identify first frost date, last frost date so that you can kind of plan around it. But the zones were to kind of give you an idea of when to plant, what to plant.

IRA FLATOW: Because climate change, the zones are changing, right? We have a– a Zoom listener wants to know, I heard that fruit grows well when they are planted with native plants. Can you verify that? Elizabeth.

ELIZABETH BUCK: Sure. So I’m going to take a little more nuance with it. I think it’s important to remember that fruit– many fruits that we grow here are not native plants. Strawberries are native. Blueberries are native. There’s some brambles and definitely other types of berries that are native. But if we’re talking about things like apple trees, they’re not from here.

I think when you start working with native plants you get a lot of benefits because you’re consciously thinking about the biodiversity and the ecology of your garden. And when you think about biodiversity and ecology, you get all sorts of good benefits, like increased pollinators, better habitat for good microbes, increased soil health.

And so my sense is that it’s probably more of– a result of the overall gardener’s awareness. And that’s always a positive thing, to be aware of all the biology and ecology going on out there.

IRA FLATOW: I think we have time for one more question. And this is from a listener in our Sci-Fri VoxPop app, with a question about wildfires and garden vegetables. Margaret from Albany, California.

AUDIENCE: I have quintus beans, which are like Romano beans. I’m concerned about the wildfires in California with all of the smoke on my vegetables, including my beans going to be OK to eat after all of the fires.

IRA FLATOW: Gary, what do you think?

GARY PILARCHIK: I never thought about that, but I would have to roll the dice and say that it’s OK. Fires have been around since the Earth’s been around. Unless there’s a chemical contaminant in your smoke, I think you just go ahead and you grow, and harvest as you wish.

IRA FLATOW: You know, what’s interesting is that these are questions we never had to think about before, did we? I mean, wildfires and the smoke spreading everywhere into people’s gardens. I mean, climate change has brought around a new reality. Elizabeth, has it not, about how we have to think about gardening? Whether it’s the temperature, or the zones, or the atmosphere?

AUDIENCE: It absolutely has. And the bulk of my job is working with commercial growers in New York state. And they’re having a hard time and they’re professionals. Things are happening, like getting 40 degree nights in the beginning of June. And everything that is going on climate wise affects all the gardens too. So it’s becoming so much more difficult to just grow.

IRA FLATOW: We have run out of time. I’m thinking about the gardeners now out in the Pacific Northwest and California with the temperatures and their lack of water that’s going on out there. That’s a different subject for another time.

Right now we’re talking about home gardening. And I want to thank my two expert guests here, who have talked about it. Elizabeth Buck, fresh market vegetable production specialist with Cornell Cooperative Extension, and Gary Pilarchik, author of the book The Modern Homestead Garden and host of the “Rusted Garden” YouTube channel.

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