092-Vegetable Planting Timeline & More: Joe Lamp’l Responds to Listener Questions

| Care, Podcast

For this week’s podcast, I polled the joe gardener Facebook Group to ask what garden questions they would like answered. This is a great community of engaged and supportive gardeners. There is never a shortage of questions. Here, I selected the most commonly-asked topics (some of which I’m asked frequently through my other social media platforms and communications) and highlight some of those specific questions here, along with some answers.

I hope you find this information timely for your garden endeavors and that this episode might help you overcome a little “cabin fever” while waiting for spring to arrive and a new growing season to kick into full gear. Let’s dive in:

“I’ve been growing my own seeds for the last few years with mediocre results. This year, I bought seed heat mats. I have fluorescent lights set up in my basement garage where there’s no heat. So, I’d like to know what you think about starting the seeds in a sunny area in my kitchen on the heat mats and, once I transplant them to larger containers, moving them downstairs under the lights.” 

Heat mats are ideal for increasing the soil temperature of your seedling containers to approximately ten degrees above the ambient room temperature. Warmer soil increases the germination rate of seeds and stimulates root growth as seedlings develop.

Heat mats should improve your results when used in a warm room of your home, but they may not be enough in a cool, unheated environment such as a basement. If a cool space is your only option, a heat mat will help; but another good step is to create a small, insulated environment.

Wrap a sheet of plastic around the rack, shelves or other area where your seedling trays are stored to establish a separate chamber and create a pocket of air warmer than the room at large. This insulated space, along with the added warmth from the heat mat, can really make a difference in your seed-starting success rate. Depending on what you’re growing, sufficient heat can be particularly important after germination for healthy foliage development.

Proper lighting is fundamental for success. Although you might think a bright, sunny window would do the trick; it’s simply not enough light to provide seedlings what they need for vigorous, sturdy growth. Providing a longer period of light at a higher intensity can really make a difference.



To understand a bit more about light duration and intensity and why they matter for seedling development, check out a recent episode on the science of light. It’s a fascinating look at aspects of light you may have never considered.

Suffice it to say that, once your seedlings have germinated, they will need more light than a sunny window can provide. I’ve found my seedlings are healthier when I provide a steady 24 hours of light at this stage. There are many lighting options – from inexpensive fluorescent shop lights to high-tech LED options.

Once seedlings begin to develop their true leaves – their second set of leaves – (that first set is commonly referred to as the seed leaves or, technically, the cotyledon leaves) you can safely back off on long-term lighting. That’s the point at which I begin to mimic natural light, with 14-16 hours of good lighting.

A key sign that your seedlings aren’t receiving sufficient light is when they become leggy. They stretch out in search of more light. Although they can recover, this leggy or lanky growth creates stress and reduces the overall health and resiliency of the plants. When seedlings are robust, they remain short and stocky.

Regardless of where you grow your seedlings and the light you use, one more good step is to provide good air flow over the foliage with a small fan. This reduces the risk of damping off – a fungal disease which kills seedlings right at the soil surface. A high-quality seed starting mix reduces potential issues with damping off as well, but good air movement is key and never hurts.

“When should I transfer seedlings from the starter cells to their grow-out pots?” 

Don’t transfer seedlings until after they have set their second set of leaves – their true leaves. A good rule of thumb is to wait until roughly 30 days have passed since germination. Ideally, the seedlings will appear healthy and sturdy by this point.

Your best indicator is to look under the seedling tray or container. If roots are beginning to emerge through the drainage holes, that’s the signal that they are ready to transplant into pots. The roots emerge from underneath the seedling containers, once they have filled the available space and are seeking additional room to spread and grow.

“What is the timeline you use for planting vegetables?” 

This is a complex question and depends on a number of variables – the type of vegetable, if it’s a warm or cool season crop, whether planting seeds or seedlings, etc.

One key factor that you need to know regardless of the variables is the last frost date for your area in spring. You can find the estimated date for your region through an internet search or by contacting your local County Extension Service. It’s also important to know the estimated first frost date in fall for your area.

Tomatoes, beans and squash are all examples of warm season crops. They require warm weather to thrive and produce. If you purchase warm crop seedlings, don’t plant those before the last estimated frost date – or if a frost is imminent, be sure to cover them overnight to protect their tender foliage from the cold temperatures.

If you plan to start seeds indoors for warm season crops, aim to get those seeds into soilless mix about 8-10 weeks before the last frost date of your area. That way, they will be sturdy seedlings, ready to plant after your last frost date has passed. If you start seeds too soon or experience a longer-than-normal period of frigid temperatures, those seedlings can get too leggy while waiting to be moved to their outdoor environment.

If you do need to postpone moving them outside due to weather, don’t worry – they can recover. Just don’t start them so early that an overextended wait indoors will be necessary.

That said, don’t feel the need to restrict yourself to planting warm season crops just once per season. You can continue to start seeds and plant seedlings through much of the summer. For example, I plant my first tomatoes outdoors around mid-April in my zone 7b garden. As a result, I tend to harvest my first ripe fruit around July 4th – always my goal.

In the warm, humid conditions of the Atlanta area,s diseases really start to take a toll in mid-summer, and pests become a bigger issue as well. So, I like to plant a second round of seedlings in mid-summer. That allows me to bypass issues during the peak pest and disease season of my area.

The second set of seedlings develops through late summer and provides an amazing crop through my warm fall months – long after my first tomato plants (and the pests and disease problems) have faded.

Cool season crops can tolerate, or even be improved by frost. Aim to plant these seedling varieties earlier in spring – about a month prior to your last frost date is a good guideline. As temperatures warm, your cool season crops will begin to fade, because they generally don’t tolerate heat well.

For a cool season fall crop, plan to get seedlings into the ground around the end of August or in early September. As temperatures cool, these crops will continue to grow and produce – often beyond the point when frost has set in.



There are several variables to determine the ideal time to plant. Be sure to learn the first and last estimated frost dates for your area.


As with warm season crop seeds, start your cool season crop seeds about 8-10 weeks before you plan to transplant them outdoors.

Many seed catalogs provide variety-specific timing information. A good example is High Mowing Seed Company. In the back of the catalog, they include a lengthy planting chart with guidelines on when to sow seeds indoors or outside based on the specific preferences of each vegetable. Those resources can take a lot of the guesswork out of gardening.

“Could you tell me what the differences in seeds are to include Heirloom, Hybrid, Open Pollination, etc. And, what does an “F1” stand for if listed on a seed packet?” 

This is an area that confuses even many seasoned gardeners.

Open-pollinated plants are pollinated through natural means – insects, wind, human interaction, etc. As long as the pollen isn’t shared with another variety within the same plant species, the resulting fruit and seed will be true to the parent plants – the parent variety.

F1-hybrid plants are intentionally cross-pollinated by humans between plant varieties. For example, a plant breeder will cross-pollinate two different varieties of tomato with the intent of producing a new plant with the best characteristics of each parent plant. This cross-pollination process is carefully-controlled and can take many years to refine and produce a stable outcome – such as larger fruit, improved disease resistance, a more compact plant size, etc.

Although I plant mostly heirloom varieties, Sungold – an F1-hybrid – is one of my favorite tomatoes, and I always include it in my garden. Sungold was produced as a result of intentional cross-breeding, and I’m a big fan of the result of all the hard work of plant breeders on this one! Sungold is a cherry tomato and, thanks to cross-pollination, it is prolific and has some of the best flavor out there. It’s popular with many gardeners.

The Juliette tomato is another good F1-hybrid example. A member of the roma-style tomatoes – it was bred for increased disease resistance, great taste and heavy production. While most of the best tasting tomatoes are heirlooms, plant breeders have produced some great tasting F1-hybrids too.

One thing to keep in mind if you save seeds from your garden: F1-hybrid seeds will not produce a true plant in the next generation. In other words – I don’t save seeds from my F1-hybrid Sungold tomatoes. Those seeds won’t produce the same Sungold tomatoes I love, because the hybrid genetics aren’t stable enough to continue into the next generation.

Here’s an important note: Don’t confuse plant hybridization with genetic modification or genetic manipulation. These are very different topics and methods of plant development. Genetic modification/manipulation occurs, not through pollination, but through alteration of plant qualities at a cellular level.

Now, let’s discuss my personal favorite – heirlooms. A plant is considered an heirloom when the seeds from that variety have been passed down for generations. Heirlooms are open-pollinated within their unique plant variety to create true seeds. In other words, Cherokee Purple tomato plants are open-pollinated with other Cherokee Purple tomato plants to create true fruit and seed.

To qualify as an heirloom, the seeds from that variety have been passed down for 50 years or more, in general. They are often noted for their story – their unique history – and/or for a special feature or trait. If you save seeds from an heirloom plant, those seeds will produce more true heirlooms.


heirloom tomatoes

My favorite tomatoes are heirloom varieties. I love the history behind each and the taste is hard to beat.


“Is there some kind of organic spray that can be used for invasive weeds and destructive insects in the garden.” 

Wouldn’t this be ideal? Unfortunately while there may be something marketed for this multi-purpose garden do-all, it won’t be safe to use on your plants without killing everything altogether. Sufficient potency to kill invasive weeds and destructive insects would require a harsh chemical.

Even when it comes to tackling just the weeds, there are no selective organic herbicides available. There are some common organic herbicides, such as vinegar and citric oils, but they are non-selective – meaning they will kill more than just your intended target.

Vinegar (acetic acid), for example, is an organic, natural treatment. Household vinegar is typically a 7% concentration, while horticultural vinegar is generally in the 20% concentration range. I strongly recommend against horticultural vinegar.

Even when diluted, all vinegar is harmful – and typically lethal – to many of the beneficial creatures we want and need in the garden. Frogs, lizards and many beneficial insects can be killed on contact with even a miniscule amount of diluted vinegar.

Vinegar is broad-spectrum and non-selective. It may do harm to the weed, but it will also harm the foliage of any plants which you inadvertently dose with vinegar too. If you use vinegar in your garden, do so being mindful of these unintended consequences and take extreme precautions.

The same is true of citric oils, however these oils aren’t very effective weed suppressors either. Citric oil will burn weed foliage, but it doesn’t impact roots without repeated applications.

The ugly truth of the matter is that weed control with organic products is difficult. Your best weapon against weeds is a 2” layer of mulch. When you add mulch over your exposed soil, most of the weed seeds in your soil won’t receive the light they need to germinate.

For those weeds which do manage to sprout, your best bet is hand-pulling – especially after a good rain when the soil is most pliable.

As for those damaging insects, there are organic pesticides available, however those products have no impact on weeds. On the other hand, they can do as much damage to beneficial insects as to the pest insects you are trying to fight. For example, Bt – Bacillus thuringiensis. It is considered a selective treatment in that it impacts only caterpillars. Yet, Bt doesn’t know the difference between a cabbage worm and a Monarch butterfly larvae. It’s killing power is just as effective on both creatures. Not good.

If you are willing to exercise a bit of tolerance for pest damage, beneficial insects will become aware of your pest population and will move in to take out the pests for you. I’ve shared a few fascinating episodes providing much more on this subject, with a couple of experts – Suzanne Wainwright-Evans and Jessica Walliser, so I encourage you to check those out before you reach for any pesticide treatment.



Many organic treatments – like vinegar – can do unintended harm. If this guy comes into contact with even a trace amount of vinegar, it will be lethal.


“I use neem oil a lot for, pests, fungi, etc. is that a good idea? Or is there a better fix?” 

Please see above. Alright – in all seriousness, neem oil is a natural product derived from a tree native to India. It functions as a pesticide by disrupting the maturity of the insect. It prevents the insect from molting from one life stage to the next. It also stops the insect from feeding. Both reactions result in the death of that insect.

Neem oil is generally safe and can be good for many pests, such as aphids. However like other organic (and chemical) pesticides, it’s non-selective.

Let’s take a look at that aphid example. Aphids can be a big pain in the garden. I get that. But – they also attract many beneficial insects, such as ladybugs. Ladybugs are most voracious and effective against aphids when they (the ladybugs, that is) are in their nymph stage. Ladybug nymphs are small and look nothing like their adult form, so you may not see them while treating aphids with a pesticide like neem oil.

It’s very likely you will take out ladybugs while taking out the aphids. As a result, your ladybug population will decline, and you will continue to fight an aphid problem.

If you do opt to use an organic pesticide, neem oil is probably one of your better options, but it’s important that you read the instructions carefully, apply carefully and don’t over-apply.

“Definitely want to hear about your perfect soil recipe!” 

Word has gotten out about my perfect soil recipe. I shared it in an episode last spring devoted to raised bed gardening. Healthy soil is much more than dirt, and there are a number of materials which contribute to the ability of your soil to provide the nutrients your plants need to thrive.

When I’m building a new bed, I fill it by following these guidelines:

  • 50% high-quality topsoil   Not all topsoil is created equally, so before you buy, check around and do a little research to make sure you’re getting good quality.
  • 30% certified compost  It’s a good idea to look for STA-certified. That is an indication that the compost supplier has met the vetting and testing criteria set by the U.S. Composting Council.
  • 20% other amendments  This percentage can be made up of one or more of other organic materials, like the following: Some of my favorites include shredded leaves (my top choice), mineralized soil blend, vermicompost, mushroom compost, finely ground bark, or composted cow or poultry manure. The more diversity you provide in your soil, the better. One key note: if you opt to use cow or poultry manure, be sure it’s been composted. The composting process is important to mellow out the nutrient level – raw manure’s high nitrogen levels can actually do harm when amended into your soil.

When in doubt on quality for any of these ingredients, a good resource can be your local garden center or County Extension Service. Either should be able to provide you references and recommendations for a supplier.

This is the blend I’ve used in my garden beds for years, and it’s a fundamental reason for the success of my garden and plant health – regardless of what Mother Nature has thrown at me. I’ve provided much more on the recipe, ingredients and cautions on what not to use in last spring’s episode too.


great soil

My perfect soil recipe incorporates a diversity of quality ingredients for great nutrients, tilth, texture, and structure.


“Do you have any advice on a simple greenhouse, for a home owner?”  

This subject could be an episode in and of itself. In fact, it will be. Watch for a greenhouse episode coming very soon. In the meantime, here are a few details to keep in mind when adding a greenhouse to your garden set-up.

No matter what size you think you will need – opt for the next largest size. Everyone who ever builds or purchases a greenhouse wishes they had more room. So, go as large as your space and budget will allow.

The purpose of a greenhouse is to create a space which insulates heat while allowing maximum light to the plants housed inside. You don’t need anything particularly fancy or expensive to accomplish this goal, but there are a few features which are important to include.

The enclosed space and ample light of a greenhouse environment can get overheated quickly, so automatic vent openers are invaluable. Most use wax for the opening mechanism, so they require no electricity. As the wax warms and melts, it expands and pushes the venting window open to allow heat to escape.

Ventilating a homemade greenhouse can be tricky, but it’s certainly achievable. If you are the do-it-yourself type, just be sure to devote some time and resources to providing good ventilation.

In hot climates, like my Atlanta-area zone 7b, the mid-summer heat is too much for even the best ventilation system. A greenhouse in full sun can quickly become an oven, but you can purchase shade cloth to provide the necessary protection from the sun’s rays.

Shade cloth comes in a variety of weights – from a light-shade to a full-shade grade. Your needs will depend on the location of your greenhouse and your climate. It may be worthwhile to have more than one weight of shade cloth on hand to keep things comfortable throughout the season.

Although I don’t recommend landscape fabric in the garden, I do recommend it on the floor of your greenhouse. Cover that with a layer of pea gravel, and you can spray water on the gravel during hot days to cool down the whole greenhouse space.

Another handy device is a wireless temperature transmitter. It can monitor and alert you to rising (or falling) temps in the greenhouse environment from the comfort of your home. No need to make continual trips to the greenhouse to check on things when you add one of these to your setup. Look for a transmitter with an alarm feature to alert you even when you are too busy to remember to check it.

If you grow seedlings in your greenhouse, monitoring the air temperature is even more important. Those tender seedlings have a lower threshold for extreme conditions. During cold days, it’s a good idea to use warm water to irrigate seedlings. Cold water can shock their roots and slow their growth. A heat or propagation mat can help to regulate the seedling soil temperature.

Using a sterile seed-starting medium is even more important when growing seedlings in a greenhouse. The tightly sealed, small environment means air will be more moist and warm than the conditions in your home. That’s a good thing for seedlings, but it can also foster disease like damping off. A sterile medium will reduce your risk of issues.

A small fan will lessen the risk of disease issues for seedlings and any other plants you keep in the greenhouse. The continual movement of air from the fan will regulate the overall temperature of the space and help prevent many disease problems.

The moist, warm and closed environment of the greenhouse makes it all the more important to sterilize containers, seed trays, tools, etc. Wash things off with a mixture of 1 part bleach and 9 parts water as another important step to proactively manage diseases in the space.

Don’t overwinter sickly plants. I can’t stress enough how quickly disease can get out of hand in a greenhouse, so play it safe.



A home greenhouse doesn’t need to be this elaborate, but there are some key points to consider for even the simplest of set-ups.


Pests can get out of hand too, so anytime it is necessary to introduce a new plant to the protection of the greenhouse, be sure to clean the foliage thoroughly to remove any pests lurking there. Whiteflies are a common problem, and they are difficult to eliminate once inside.

Many gardeners rely on those yellow, sticky traps to manage pest problems. I’m not a fan of those in a greenhouse. After all, beneficial insects make their way into this space too, and they are just as likely to be caught up on those traps. I’ve even seen small birds fall victim to these seemingly benign pest management tools.

Learn what the eggs and larvae of beneficial insects native to your area look like. That way, you are more likely to recognize them if they make an appearance in your greenhouse. Those can be great allies in a healthy greenhouse environment.

Lots more to come on this much-loved aspect of gardening, so stay tuned for the future episode with additional advice on this subject.

“I am very curious about season extension techniques and how to start implementing them?”

There are a number of ways to extend your garden season. For early frost days, floating row cover can be a lifesaver to protect plants overnight. I suggest you look for spunbond polyester cloth covers, commonly referred to as reemay. However, row cover offers only light protection, so if you want to garden more deeply into the cold months of winter, plastic covering will do a better job.

I recently shared an episode featuring Eliot Coleman, the king of season extension. Eliot and his wife, Barbara Damrosch, garden all year long – in Harborside, Maine. So, they know a thing or two about extending the season. Check out that episode for details on how Eliot uses plastic to create a climate similar to zone 7 – even in the midst of frigid nor’east temperatures.

Low tunnels can be a great option for protecting crops through the winter. Build low tunnels using PVC pipe or electrical conduit secured on either side of the garden bed into the ground. Place plastic sheeting over the pipe or conduit and seal the plastic to the soil surface using sandbags or some other means which will stand up to winter winds.

I demonstrated this on an episode of my PBS show, Growing a Greener World®, so you can watch for yourself. It’s an easy do-it-yourself project, and it can have you enjoying vegetables fresh from your garden through every month of the year.


low tunnel

Low tunnels – whether on a raised bed or over an in-ground bed – are a proven method to extend your growing season into even the coldest weather.


“What would you consider to be your biggest garden failure as well as most important lesson learned?”

As a trained horticulturist, garden industry expert and well-seasoned gardener; I know my stuff – but boy, have I had my share of failures. The truth is, I don’t think of them as failures. I see them as opportunities.

I believe every gardener should strive for “failure.” It’s these experiences which can be the best way we learn. It’s so important – and rewarding – to try new things, push our boundaries and knowledge, and observe the cause and effect of those actions.

Plants are much more resilient than we give them credit for. More often than not, they will recover from our garden mistakes – as long as we are paying attention and adjust before the plant suffers the ultimate consequence!

Take one of my mistakes, for example. I suffer from paralysis by analysis. I always want to put a new plant in the perfect place. Even though I know that if I regret a placement, I can dig that plant up and move it to a better location – I’m so focused on wanting it to look good right from the start, that I fail to start. Fortunately, my hydrangeas are very resilient – and very patient.

I’ve had a large group of hydrangeas sitting in containers for over thirteen years. It’s not my intention that they remain as container plants. I simply never feel like I find the absolute perfect spot for these treasured plants. In fact when I moved from Atlanta to North Carolina, I rented the largest moving van available, just so I could trek my mobile hydrangea collection with me.

Several years later, they were still in their pots and moved back with me from North Carolina to the GardenFarm™ just outside of Atlanta. Seven years later, I still haven’t found just the right spot. So, these durable shrubs remain in their containers – thirteen years and going strong.

I regret not getting started sooner with choosing where to place a plant – just like all those hydrangeas. Some day, I’ll overcome my paralysis and start planting. Just not some day soon. Until then, I’m looking for the opportunity for other failures – experimenting, trying new things, continually learning.



I’ve managed to get a few of these hydrangeas into the landscape but most are still waiting in containers as I mull over the perfect spot.


What mistakes or failures have you experienced? I encourage you to share yours in Comments below for the same reason I share mine – because in so doing, we help other gardeners. Our shared lessons learned help each of us in one way or another. I hope that, by being open about my mistakes that I can help you become a better, smarter, more confident gardener.

Links & Resources

Episode 007: Organic Weed Control with Jeff Gillman

Episode 008: Organic Pest Control with Jeff Gillman

Episode 029: My Five Biggest Gardening Mistakes of All Time (and What I Learned From Them)

Episode 049: When Good Bugs Eat Bad Bugs: The Business of Beneficial Insects

Episode 067: Predatory Beneficial Insects: Feared Foes of Garden Pests, Pt. 1

Episode 078: Why Buy Organic Seeds: Fixing a Broken Food System, with Tom Stearns of High Mowing Seeds

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

Episode 086: Timeless Gardening Principles, with Barbara Damrosch

Episode 088: The New Organic Grower: 50-Years in the Making, with Eliot Coleman

Growing a Greener World® Episode 623: Year-round Growing with Eliot Coleman

The New Organic Grower, 3rd Edition: A Master’s Manual of Tools and Techniques for the Home and Market Gardener, 30th Anniversary Edition, by Eliot Coleman

U.S. Composting Council

Beginning Gardener Fundamentals – Online course details

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

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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 “092-Vegetable Planting Timeline & More: Joe Lamp’l Responds to Listener Questions”

  • Mark Wolfe says:

    I live in the Kansas City area and Cedar Mulch is very popular. Is Cedar Mulch safe to use to top my raised beds? Put another way, other than rubber and colored mulch, is there any mulch material you would avoid? Cedar, Cypress, Red Wood, etc.? Thanks!

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