095-Tomato Seed Starting Update: Innovations and Inspiration, with Craig LeHoullier

| Grow, Podcast

For this week’s podcast, I’m catching up with a good friend and frequent guest, Craig LeHoullier. Craig is responsible for the revival and development of many favorite heirloom tomato varieties, and he is a pioneer in a dense-planting technique for seed starting.

Craig is always experimenting. One of his recent projects involves testing germination rates of older seeds. He’s had successful germination from seeds several years old. It takes longer for the germination to occur, but with a little patience, Craig is finding that there is still life in these old seeds. Some of the seeds he planted this year had been in storage for nineteen years.

Craig doesn’t take any particular care when it comes to storing his seeds. He contains them in small manila envelopes marked with the varietal name. They aren’t refrigerated or kept under any special conditions. Craig found that most of his eight and nine-year-old eggplant and pepper seeds took up to 37 days to germinate, but his rate of success is high.

He’s still patiently waiting to see if the nineteen-year-old seeds will push through the surface.

Some of his fourteen-year-old seeds took a little longer to sprout too, but that’s due in part to Craig having forgotten to plug in the heat mat. Warm soil aids in germination, so the lack of supplemental heat slowed things down a bit.

Even the seed-starting masters miss a step once in a while!


Craig LeHoullier

Craig LeHoullier is a tomato expert, seed starter extraordinaire and a good friend. (photo: Courtesy Craig LeHoullier)


I’ve been hearing from more gardeners ever this year who are on the seed-starting journey. Many of them, like me, are also following Craig’s dense-planting technique.

Craig and I discussed his technique in a podcast series last year. He fills each cell or container with a large quantity of seeds. As they germinate and mature, he teases apart the seedling clusters and transplants each seedling into its own container.

I utilized dense-planting for my seeds last year and loved it so much that I continued the practice for this year’s seeds too. I’ve been planting at least 16 seeds in each 4”x4” tray cell, but Craig often plants even more densely.

This approach isn’t to improve seedling health. It’s just a great space saving technique. Craig didn’t have much room to work with, but he wanted to sell a lot of seedlings. If you’re short on space or materials, check out the podcast series where we discuss this at more length, or you can watch the episode of Growing a Greener World® where we filmed Craig’s seed-starting and transplant processes.

I’ve been doing some experimenting of my own this season. Last year, I top-watered all my seedlings. I watered them from above with a watering can. This year, the only water I’m providing is from the bottom tray. I pour about a half an inch of water into the solid tray which holds my seed trays. The soil wicks up the moisture through the drainage holes.

I’m finding that this year’s seedlings are less stocky than last year’s group. My 2019 seedlings are taller and less tough. This may be related to bottom-watering, but there are other possible culprits.

Just as out in the garden, every year brings variables to your seed-starting process. Some you can control, others you can’t.

Another variable for me is lighting. I opted to provide supplemental lights 24/7 until the seedlings developed their true leaves – their second set of leaves. Then, I transitioned to a sixteen hours on and eight hours off cycle, which is the schedule I followed exclusively all through last year’s process.

So, are my seedlings tall and fleshy because of the different light spans or due to my altered watering process? I’m not sure yet, but I’ll be experimenting further to see if I can find the answer.

In Craig’s experience, there are many aspects which can contribute to seedlings becoming leggy. The type and duration of light provided, the distance the light is kept from the foliage, the temperature in the room and of the soil, the planting medium and whether or not that medium includes trace nutrients – each of these elements will have an impact on your seedlings.



For the past two years, I’ve been using the dense planting technique for my seed starting. I’m able to fit many more seedlings in the small space of my seed-starting room (aka entry hall to my office).


The thing is, seed-starting just isn’t an exact science. There are a few critical success principles to follow – which I covered during last week’s podcast – but the rest falls to judgment and observation.

Craig and I both follow a touch and feel approach to seed starting. We try different things, watch for the results, and correct potential issues when we observe trouble.

You win some, you lose some. Although we, as gardeners, oftentimes mourn the loss of every seedling; it’s important to remember that the loss is minimal. The cost of a packet of seeds is so small, that failure only sets us back a dollar or two for more seeds and a few weeks’ behind schedule.

I’m not concerned about my overly-tall seedlings either. Most are tomato plants, so when I transplant them to their own containers, I’ll bury them deeply. The buried stem will develop more roots, and I’ll still wind up with strong, healthy tomato plants.

Plants are so much more resilient than we tend to give them credit for. Disease, frost or a pest snipping off the top shoots can be lethal to plants – but everything else is correctable.

Once, Craig had too many Sungold seedlings and not enough larger containers appropriate for transplanting. The extra seedlings remained in their small 3.5″ cells until they grew to about 3’ high. They weren’t healthy in that environment. In fact, they lost all their leaves but those at the very top of the plants.

When Craig was finally able to transplant each of these restricted plants into a larger container, they began to flourish and produced a great crop of tomatoes. This experience is a great reminder that plants have a strong, natural determination to survive.

So, have the courage to go for it, and see what happens! Observe and learn from your results. Take notes. That’s a great way to keep track of what might have gone wrong, so you can avoid the same misstep the next time. As importantly, it will help you identify what might have brought you your best results ever.


basket of tomatoes

There is a mind-boggling array of tomato varieties available to grow. Experiment with something new each year. You’ll find your favorites – and which work best in your space – but it’s a good idea to continue to try on something new for size.


In gardening, confidence comes with experience. With each year, it’s the mistakes you make which will teach you the most about what works and what doesn’t.

On the subject of trying new things, Craig is hardening his seedlings off earlier than ever this year. He’s been moving seedlings out into the sun for an hour ever since they were just 2” high and in temperatures as low as 40 degrees Fahrenheit.

Since those seedlings are too young to transplant and are still grouped in fewer trays, it’s more efficient to move them twice daily. Craig is also finding that this early exposure to outdoors encourages sturdier growth too.

Although they can take cool temperatures, wind and rain can take a toll on young seedlings. If they become bowed over, it can be difficult for them to recover. So, Craig is careful to avoid placing seedlings outdoors in windy or rainy conditions.

Craig has also begun transplanting seedling clusters. Since he’s planted 20-30 seedlings in a cell, he’s finding that the roots of the cluster need more room to expand, but the seedlings themselves are too young and tender to separate into their individual containers.

By transplanting the whole cluster into slightly larger containers (4” x 4”), Craig is providing the crowded cluster more room to develop roots, and he needs to water less frequently. It’s an extra step, but it works well for Craig.

You’ll find the method that works best for you too. You just need to experiment.

Fertilizing Seedlings

I’ve never been one to provide seedlings with fertilizer. The seed has what it needs to thrive until it sets its true leaves and begins to generate energy through photosynthesis.

This year, I’m experimenting with fertilizer too. I’ve selected three trays of seedlings of the same variety and at the same growth stage.

I’m misting the foliage of one tray with a liquid kelp fertilizer product. Each time I bottom-water a second tray, I’m adding an OMRI-approved, liquid, organic fertilizer to the water. For both fertilizer products, I’m following the instructions on the packaging carefully. If you use any fertilizer product, you should adhere to those instructions too.

The third tray of the set isn’t receiving any supplemental nutrients. They’ll have light, water, and warmth from heat mats – but otherwise, these seedlings are on their own.

I can’t wait to begin to observe any notable differences in seedling health through the next few weeks. I’ll be sharing short video and photo updates on progress on my Instagram channel. Join me there as I document this seedling journey, and you can watch and learn from the process too.

I hope all the seedlings in this experiment thrive – but in the end, it’s the learning that matters most. Whatever happens to those seedlings, the lessons I take away and share with others will be worthwhile.


Craig Lehoullier

Craig grows thousands of seedlings and mature plants in containers – like the grow bags seen here – in the driveway of his North Carolina home.


I asked Craig if he had any experience adding compost or vermicompost to his seed trays, since it’s a question I hear often. Although he hasn’t tried this, he doesn’t believe it would do harm as long; as you don’t add foliage from the nightshade family of edibles (tomatoes, peppers, eggplants) which could carry forward to affect your seedlings.

Have you added compost or vermicompost to your seed-starting routine? I’d love to hear about your experiences in the Comments section below.


Craig has been using 40-watt fluorescent shop lights for years. He is curious to try LED lights, but has been so busy, he still hasn’t had an opportunity to change his set up. It goes without saying that those 40-watt fluorescent bulbs have been serving Craig well. His seedlings grow beautifully.

I used the same shop lights for years too, but last year, I made the switch to LED lights. I love the 300 watt LED lights I purchased. It took a while to find the correct distance to set them above plant foliage, but with a little trial and error, I found 25” is the perfect distance for my set-up. The smaller units and efficiency of the light have been big pluses for me.

Although many gardeners like to use the LED grow lights that have only red and blue lights – I prefer the white light of full-spectrum bulbs. Red and blue are a more efficient light frequency for plant growth, but I have to look at my lights every day. So for me, full-spectrum was the ticket.

Seed-borne Disease

Did you know that many of the most common plant diseases can be transmitted through the seed? This is a relatively new discovery. Fusarium wilt, for example, is a soil-borne disease. However, a recent study found that fusarium wilt is just one of many of the “who’s who” of plant diseases that can also carry forward in the seed of a plant affected by the disease.

Cornell University researchers found that heat-treating seeds prior to planting was an effective way to kill any lurking disease pathogens. This year, Craig has been experimenting with heat-treating. He purchased a small device for just this purpose. These units are commonly available, but you can achieve the same purpose without any special equipment.

Disease pathogens are eradicated when the seed is immersed in water that is approximately 130 degrees Fahrenheit for 25 minutes. The hot water that comes out of your kitchen faucet is probably warm enough to fit the bill here, so this doesn’t need to be complicated.

Once Craig heat-treated the seeds with his equipment, he dumped the seeds into a planting cell and proceeded as usual. This is an easy and good proactive step if you save seeds from your plants year after year.



Recently, it’s been discovered that many of the most common plant diseases can be transmitted through the seed. If you save seeds from your fruit, consider heat-treating those seeds before planting to eradicate any potential disease pathogens.


Planting Medium

I asked Craig for his thoughts about the variations of seed-starting mix available on the market. He and I both use a commercial-grade soilless mix. I touched on this more in my podcast last week.

When you head to the big box store or local nursery to purchase your seed-starting supplies, there might be a lot of choices for your soil. Be sure to purchase soilless mix or seed-starting mix for your seeds.

Bags labeled topsoil or garden soil – or even soil straight from your garden – can work. Seeds will germinate in these heavier soils, but these soil options increase your risk of a few things which can go wrong.

Soilless mixes and seed-starting mixes are typically sterile (although it may not say so on the bag). That’s important because tender seedlings can fail quickly from disease. When a mix is sterile, disease pathogens have been eradicated from the mix. That translates to a lowered risk of disease.

The delicate roots of seedlings need a light and airy medium to develop well. Soilless and seed-starting mixes are designed for this. They typically include a mix of shredded bark, peat moss, vermiculite, perlite, coir, and/or surfactant.

Topsoil or garden soil are heavy and dense and increase the chances that seedling roots will remain too wet. Soilless and seed-starting mixes hold moisture well but are designed to drain well too.

Don’t skimp when it comes to your planting medium. Whether you’re buying soil for your garden, potting mix for your containers, or soilless mix for your seedlings; look for a good quality product. If your local options are limited, there are mixes available through many online seed suppliers, and these can be good options.

If you blend your own seed-starting mix with some of the ingredients listed above, be sure you don’t rely too heavily on peat moss. Unlike coir, peat isn’t a sustainable product. Once the peat available to us on this planet is gone – it’s gone for good. It’s also very difficult to re-hydrate peat once it’s dry. So, it’s important to include materials which will provide moisture balance.

If you’re in doubt about the sterility of your seed-starting mix, head for the kitchen. By baking the mix in a tray covered in foil for approximately half an hour – or until the temperature of the mix is between 180 and 200 degrees Fahrenheits , the materials will be sterilized. Keep the tray covered with foil as it cools off to be sure of successful sterilization.


Ripe tomato

There is nothing like the taste of a freshly-picked home-grown tomato – especially when you started the plant yourself, from seed!


Dwarf Project Update

If you’ve read descriptions of any of the heirloom tomato varieties available through most seed companies, you’ve probably seen more than a few credited to Craig LeHoullier. He’s devoted a lot of time and effort to developing many beloved heirlooms to be available for purchase by gardeners everywhere.

Craig has also been devoting time to a new type of tomato – the dwarf tomato. Many heirloom tomatoes are indeterminate – meaning they will continue to grow to enormous size unless they are kept under control. Determinate varieties remain at a more compact size, but they only set on fruit once, then they die.

Dwarf tomatoes are the best of both worlds. They continue to produce great-tasting fruit, like an indeterminate, but they only grow about half as tall, like a determinate. Dwarf tomatoes are a great option for growing in small spaces or to grow more varieties in a space that may only allow for a few massive indeterminates.

Craig began working on dwarf variety development way back in 2005. Thanks to help from 500-600 volunteer gardeners, there are now just over one hundred dwarf varieties available for sale. An additional 25-30 varieties will be released next year.

All of these dwarf varieties are open-source. In other words, they are not patentable, and they will be freely accessible to all gardeners – forever.

At the end of 2018, Craig decided to bring his enormous dwarf development project to a close. There is still a little work to do, and you can keep up with his latest news on dwarf varieties by joining his Dwarf Project Newsletter.

He’s also been writing a book on the subject. Watch for this publication sometime next year. If you loved Epic Tomatoes, odds are good that you will enjoy this upcoming book just as much.


Black Krim seedlings

I love and grow several heirloom tomato varieties, and Black Krim is one of my favorites. It’s thanks to Craig that gardeners have access to many of today’s most popular heirloom tomatoes.


In the meantime, Craig has a number of speaking events coming up throughout 2019. If you happen to cross paths, he encourages you to say “Hello!” And I encourage you to thank him for all the great work he’s been doing for tomato-loving gardeners, like me, everywhere.

Have you listened to my conversation with Craig yet? If not, you can scroll to the top of the page and click the Play icon in the green bar under the title. Our talks are always a lot of fun – plus you’ll hear a few more stories about his experiences and why he compares starting plants from seed to cooking up a recipe. I think you’ll enjoy it.

Links & Resources


Episode 037: Starting Seeds Indoors: The Non-Negotiables for Success, Pt. 1

Episode 046: Organizing Your Gardening Life

Episode 083: Gardening Indoors: The Science of Light, with Leslie Halleck

Episode 094: How to Start and Care for Seedlings Indoors: My Steps for Success

joegardener YouTube: The Best Ways to Plant a Tomato

joegardener YouTube: How to Top Tomatoes

Beginning Gardener Fundamentals – Online course details

Beginning Gardener Fundamentals – Registration wait list: Sign up to be notified about the next class!

joegardener Newsletter

joegardener Facebook

joegardener Facebook Group

joegardener Instagram

joegardenerTV YouTube

joegardener Twitter

Growing a Greener World® Episode 803: Epic Tomatoes With Craig LeHoullier


Craig LeHoullier

Craig LeHoullier Dwarf Tomato Project Updates

Epic Tomatoes

Cornell University Vegetable MD Online: Managing Pathogens Inside Seed with Hot Water

Corona® Tools – Our podcast episode sponsor and Brand Partner of

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

0 Responses to “095-Tomato Seed Starting Update: Innovations and Inspiration, with Craig LeHoullier”

  • Lorri Maus says:

    Hi Joe and Craig, have you considered using a sous-vide immersion circulator which is normally used to cook food in plastic bags in a water bath to heat treat your seeds? The temperature can be set and held and the water bath can be large enough to hold lots of packages of seeds at the same time. It could serve two purposes. When you are done heating your seeds you could use it to cook your food. Great podcast.

  • Nancy Wu says:

    Thank you, Joe and Craig, for another information-filled podcast! I’m really glad to hear about what Craig is doing with his seedlings by conditioning them to the outside elements early on. I have always done that as soon as my seedlings emerge. Of course, I live in Northern California and our winters are reasonably moderate. I usually have about 400 to 500 seedlings per season, and this early conditioning has produced healthy seedlings for me over the years. I do take the seedlings inside at night until the night temperature reaches the low to mid-40’s.I will definitely try the hot water method to sanitize/disinfect not only tomato seeds, but other seeds that may carry diseases. I’m always learning a lot of great information from you. Thank you, Joe and Craig!

  • Joe Lamp'l says:

    Hi Lorri. I have not. But is sounds like a great option. And besides, the unit Craig was talking about is currently not available on Amazon. Thanks very much for this information.

  • Joe Lamp'l says:

    Hi Nancy. You’re welcome. Thanks for listening. Glad you enjoyed.

  • Timothy Blair says:

    Hey Joe, thanks for the podcast! I’m a rookie gardener, and finding your podcast has been a godsend. I live at the Jersey shore and I’m planning on building raised beds this spring. I started a compost bin using your pallet idea and I out a lid on it for critters. ???? And I started some broccoli, pepper and tomato seedlings and have them setup under an old shop light in the basement. Just recently it seems the health of the broccoli seedlings has gone down .a lot of the baby leaves have wilted and some of the seedlings have started to fall over. Any idea why? I’m not running a fan, like u show in your setup.Thanks and keep up the great work!Tim

  • Timothy Blair says:

    Joe,I have seen t8 led bulbs for the traditional shop lights. U have to modify the wiring, but that shouldn’t be too hard. Do u think they would work better than standard t8 shop light bulbs?Thanks,Tim

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