Tag Archives: cool season

Some Like It Hot and Some Like It Cold

warm season tomato plants for sale in March will not like the cool evenings if planted in the ground

One of my first lessons in growing vegetables and herbs is learning the plant’s preference for temperature. To keep it simple, there are cool season and warm season crops. Getting to know what the plant prefers determines when to buy/plant, what to buy/plant, where to buy/plant, and when to harvest/eat!

In the mid-Atlantic area, typical cool season plants are anything in the cabbage family (cabbage, broccoli, collard, Brussels sprout), lettuce, pea, kale, chervil, dill, cilantro, leek, scallions, radish, spinach, arugula, beet, pak choi or bok choy, carrot, mustard, parsnip, turnip, and Swiss chard.

cool season lettuce for sale in March will like the cool temperatures if planted in the ground

Some can continue to grow well during the summer such as spring onions and Swiss chard. Other cool season lovers “bolt” when it warms up in May/June. For example, cilantro will bolt, that is, flower and set seed, in May. This is good if you want the seed, also known as coriander, but bad if you want to continue to harvest the leaves. When the plant bolts, the leaves become bitter and eventually the plant will die because it is an annual.

Most people associate the warm season edibles with summer itself. These include tomato, basil, fennel, eggplant, pepper, corn, summer/winter squash, zucchini, melon, watermelon, cucumber, okra, and pumpkins. These will not tolerate the frosts we may get in the spring evenings so it is best to start them outdoors after the last average frost date in mid-May.

Frequently you will see both types of plants for sale as early as March. These photos were take at a local hardware store in March last year. Basil, a summer lover, is especially sensitive to cold. If one were to purchase these basil plants and put them in the garden unprotected they may die because there is still the likelihood of frost in early spring.

basil plants for sale in March may even die from a late spring freeze

In my zone 7 garden, the cool season plants/seeds should be started outside in mid-March to the beginning of April. The warm season plants/seeds should be started in early May to the end of May. If you do not know what your vegetable or herb prefers, there are several ways to figure this out:

Read the seed packet or label
Read seed catalogs
Research on the internet
Read local gardening books
Visit garden nurseries and ask knowledgeable staff.

The books I found most useful books for this area are listed below and are easy to get from the library or bookstore. Knowing the plant’s preference will help you figure out when to start your seed and/or when to purchase plants.

The Week-by-Week Vegetable Gardener’s Handbook by Ron Kujawski & Jennifer Kujawski (Storey Publishing, 2010)
The Timber Press Guide to Vegetable Gardening in the Southeast by Ira Wallace (of Southern Exposure Seed Exchange) (Timber Press, 2013)
The Year Round Vegetable Gardener by Niki Jabbour (Storey Publishing, 2011)
Gardening in the Mid-Atlantic, Month-by Month by Andre and Mark Viette with Jacqueline Heriteau (Cool Springs Press, 2008)

broccoli for sale in March will thrive in the cool season

Tips for Starting Seeds in Your Garden: Planting in the Spring

lettuce in container

Recently, I posted an article called Tips for Starting Seeds for Your Garden. The post was about starting seeds and the importance of distinguishing between warm versus cool season plants or seed. It further explained how and when to sow seeds for warm season plants. This is the second part of the post: a focus on cool season plants.

Starting Seeds in Ground or Containers

In my zone 7 Northern Virginia garden, there are many vegetable and herbs that I can start growing outside in early spring. This means I don’t have to start them indoors under lights. Not only do these particular plants prefer cool temperatures, a light frost should not harm them. I tend to start most of my cool season plants by seed in containers on my deck. Container soil is warmer than ground soil. Also, it is easier to check on them by walking on a wooden deck than to have to trample through wet, soggy soil in cold weather. By summer, most of these types of plants have bolted (i.e., flowered and gone to seed so leaves are bitter). After pulling and discarding into the compost pile, I re-stock my containers with warm season annuals such as different types of basils and bush beans.

When to Sow Seeds in Early Spring

Using davesgarden.com and my zip code, I calculated my average last frost date to be April 30. March and April are still cool and there is a possibility of a frost or even snow. From the list of cool season plants or seeds I want to grow, I calculate which I can start at what number of weeks before April 30 and which would benefit from containers on the deck or directly into the soil. If a seed packet does not provide this information, try asking your local extension agent, online seed catalogs, or read a printed seed catalog or a gardening book. A few online seed catalogs that provide quality descriptions for this are Burpee, Johnny’s Selected Seeds, Botanical Interest, Southern Exposure Seed Exchange, and Renee’s Garden.


chervil is a spring herb

Sowing Often for Continuous Harvest

For some cool season crops, sowing every couple of weeks ensures a continuous harvest until summer. For example, our family likes to eat lettuce and spinach so if I start sowing in early spring and again every other week, I will be able to continue to pick leaves for a family of four up until summer. By summer, the weather will be too hot to germinate spinach and lettuce easily.

spinach seedlings

direct sow spinach seedlings in container

Check if the seed package recommends growing in soil or if they can be grown in a container. If you only need a little arugula, grow in a shallow container. If you only need one borage plant, grow in a larger container (it is a larger plant). Chervil is so ephemeral it is best to grow in a medium container so you can access and harvest as much as possible. For plants that tend to flower and drop seed, I find it helpful to have a patch set aside. I have parsley, cilantro, and calendula patches in the backyard so I sow the seeds directly in those patches. Of the plants below, peas are the only ones that need vertical structure. They should be planted next to a trellis and “trained” to wrap around it. I grow sugar snap peas in the ground next to a wire trellis but there are some variety of peas that can be grown in containers with stakes. Here are common cool season plants that can be grown by seed:

  • Alyssum
  • Arugula
  • Asian greens
  • Beets
  • Borage
  • Calendula
  • Carrots
  • Chervil
  • Chinese cabbage
  • Cilantro
  • Dill
  • Endive
  • Greens
  • Kale
  • Kohlrabi
  • Lettuce
  • Mache
  • Mustards
  • Nigella
  • Pak choi
  • Parsley
  • Peas
  • Radish
  • Spinach
  • Sweet peas
  • Turnips

My Cool Season Seed Plan

Just before March 15

Burpee and Botanical Interests Sugar Snap Peas: Soak overnight in water and then plant seed in small plastic pots with soil. When 2 inches tall, transplant outside in ground against trellis. No need for indoor lights.

March 15

April 1

  • American Meadows Scarlet Nantes carrot, sow in large deep container on deck and in ground
  • Renee’s Garden Slo-Bolt Cilantro, sow directly into cilantro patch in ground

April 15

  • Repeat lettuce, seed, radishes, and kale
  • Start borage in large decorative container
  • Start arugula in medium container
pak choi

direct sow pak choi seeds in ground


Tips for Starting Seeds for Your Garden


Tuscan melons get a head start when start seed indoors

Starting seeds now for the garden is tempting. Racks of seed packets with their pretty images of fresh vegetables and cut flowers are like heart-shaped boxes of chocolate. Each packet is a morsel, a promise of something good to come. Starting seeds is like eating chocolate, who can resist?

As with chocolate, however, some restraint is needed. February feels like it is time to sow seeds. Surely a garden center full of seed packets is sending us a message. But before you start, here are a few tips on when to start which particular plant. This is a two-part article: this article will explain the difference between cool and warm season plants and when to start warm season plants. The subsequent article will cover cool season plants.

Learn which plants prefer warm versus cool weather

The first step is to make a list of what you want to grow and/or your seed packets. From that list, identify which plants prefer cool or warm temperatures.

For example, if you wish to start seeds of tomatoes and cilantro, mark tomatoes as a warm season plant. Plant tomatoes outside when there is no danger of frost. Cilantro prefers cool weather and can tolerate a light frost.

If you don’t know, ask your local extension agent, look online at seed catalogs, or read a printed seed catalog or a gardening book. A few online seed catalogs that provide quality descriptions for this are Burpee, Johnny’s Selected Seed, Botanical Interests, Southern Exposure Seed Exchange, and Renee’s Garden. Just type in the plant name in their search bar and don’t worry so much about the cultivar for now.


Tomato transplants in an Earthbox in May

Learn your average last frost date

Focusing on the warm season plants for now, identify your average last frost date. Using davesgarden.com and my zip code, my risk of frost in my Northern Virginia zone 7 garden, is from October 13 through April 23. I am almost guaranteed not to get frost from May 9 through September 29. I arbitrarily picked April 30 as the day when I can move my transplants from inside to outside to harden off. Picking the end of a month makes it easy to remember and to calculate weeks.

Using April 30 as the marker, count back the number of weeks it takes for that seed to germinate and reach transplanting size. This information should be on the seed packet but if not go back to the original resources I listed above. My tomato seed packages say “start seeds 6 to 8 weeks before average last frost” or “before transplanting.” Keep in mind that this is only to get a jump on the season. You can always start seed outdoors after the danger of frost has past but quite a few weeks of growing season would be lost. Six weeks from April 30 is mid-March, which is when I would sow my tomato seeds in small containers under lights.

Purchase lights to starting warm weather seeds indoors

Starting seed by a window does not provide enough light. The seed container has to be just a few inches under the florescent tubes or special grow lights. Therefore if you are interested in growing from seed, invest in lights but you can use cheap fluorescent tubes from hardware stores. Once you turn on the lights, you keep them on for 14 to 16 hours every day until you move the plants outside.

Decide which seeds to start under lights

Your indoor light system becomes prime real estate. Within the category of warm season plants, identify which seeds should be started indoors in this prime real estate section, i.e., need a head start before the end of April. Separate that list from those that could be started outdoors in the beginning of May. For example, because beans germinate and grow quickly to produce a harvest, start them outdoors in May and save the prime real estate for tomatoes that need a month and a half head start. Identify the number of weeks recommended for starting seeds indoors for each plant. Usually one starts tomatoes, peppers, eggplants, broccoli, cabbage, cauliflower, collards, onions, celery, and Brussels sprouts indoors to get a jump on the season. Start beans, corn, watermelons, zinnias, sunflowers, summer squash, cucumbers, pumpkin, and basil outdoors in May.


Roselle is a tropical plant that needs a head start

This is an example of what my list looks like for starting seeds of warm season plants under lights. I will try several varieties of pepper, tomatoes, and melons, which takes up even more space under the lights.

March 1: Eight weeks prior to average last frost date of April 30

March 15: Six weeks prior to average last frost day of April 30

April 15: Two weeks prior to average last frost date of April 30

Get Your Seed Catalogs Now and Plan for Next Year!

Decemberseedcatalogs2014 001Over the Thanksgiving weekend I had the honor of being a guest on the Garden America radio show, formerly known as GardenLife. Garden America is a nationally syndicated, live talk show hosted by Sharon Asakawa, John Bagnasco, and Bryan Main. They are in San Diego but Sharon had read my blog and contacted me so we arranged for me to be called in on a Saturday morning. Sharon, John, Bryan and I talked about growing vegetables, seed catalogs, and lessons learned from my 2014 gardening season. One of the points I made was that many seed companies have produced their catalogs for the 2015 growing season and are either available now or will be in a few weeks. Most are free, full-color resources that describe common edibles and the requirements for growing them from seed. Among the catalogs, specific details such as average seed life, insect problems, and germination rates may or may not be mentioned so I suggested that people contact several companies and get a few catalogs to compare and contrast the descriptions.



Keep in mind that catalogs lists the plants in alphabetical order, but nature does not. The first lesson in edible gardening is to learn which plants prefer cool temperatures and which plants prefer warm temperatures. Re-arrange the plants in the catalogs by cool and warm (the catalog should indicate this but if not look at your other catalogs). If you had two copies of one catalog, you could cut and paste and re-arrange them. For a list of seed catalogs, check out my page/tab entitled “seed catalogs” at the top of my blog site.

spinach seedlings

spinach seedlings

The other point I made on the radio show was that many times, people new to gardening are intimidated because they think they have to dig up the sod in the backyard, build raised beds, or install an indoor lighting system. There are some plants that will grow from seed in a simple container, outside.  The containers can be used pots from plants you have already bought at the nursery or new, as long as they have drainage holes. Some herbs and veggies can be grown in pots with as little as a six-inch depth. The plants listed below will grow easily from seed started outside, using potting soil from a hardware store or nursery. They are not particular about water fluctuations nor are they heavy feeders. The cool season for us in Virginia is end of March to beginning of May, sixty degrees to low seventies. The warm season is after the average last frost, which is around Mother’s Day, low seventies to eighties.

Cool season, six-inch depth

Chives, Cilantro, Lettuce, Radishes, Scallions, and Spinach

Cool season, twelve-inch depth

Broccoli raab or rapini; Carrots, baby; Dill, Kale, Mibuna, Mizuna, Mustard, Mache, Nasturtium, Pak choi, Peas, Swiss chard, and Tatsoi



Warm season, six-inch depth

Basil, Chives, Lemon balm, Radishes, and Scallions



Warm season, twelve-inch depth

Beans, bush; Carrots, baby; Nasturtium, and Swiss chard

If some plants are listed in both cool and warm season, it is because they can tolerate both if slight adjustments are made such as cooling them down in the summer with morning sun and afternoon shade or starting new seed again throughout the gardening season. For more information on the plants, consult your seed catalog. Pick a few from this list that you are most interested in eating and order the seed packages for next year. To save on costs, find a seed buddy so you can share the seeds from each packet. You too can grow an edible garden!

Fall Vegetable Gardening

This past July, popular seed companies announced that it was time to start the fall vegetable garden but I dismissed it as it was high summer and I was rolling in red tomatoes and yellow peppers. Now, as the tomato plants begin to yellow and the peppers turn red, I am focusing my attention on cool season veggies in hopes of reliving the greens I enjoyed this past spring. I did not plan for it though, it caught me by surprised. August is a time for harvesting and processing the summer bounty while at the same time planting another round of seeds for the fall/winter/spring edibles, depending on what you plant and if you can extend the season with covers. I was fortunate enough to have seed left over from the spring and planted pak choi, sugar snap peas, lettuce, scallions, spinach, and carrots both in the garden bed and in containers.

spinach seedlings

spinach seedlings in a basket

Last weekend I attended a 90-minute presentation called “Fall Vegetable Gardening,” where Libby Good, a Virginia Cooperative Extension Master Gardener, expanded the concept of fall vegetable gardening to include planting crops to harvest before frost or that can overwinter, planting cover crops to add nitrogen, extending the season with cold frames or row covers, garden clean up, and overall getting ready for the next year. Libby explained that planting in the fall has advantages: the soil is workable, the air temperatures can be cooler with less direct sun, the moisture levels can be higher, and there can be fewer insects and weeds. “Most fall veggies don’t rely on pollinators and are high in nutrition,” she said.

sugar snap pea seedling

sugar snap pea seedling

Libby also explained that if you are starting seed or buying transplants you have to first determine your frost date, which Libby says is around Halloween in the Northern Virginia area. Then you have to work backwards to determine when to plant the seed or transplant. But the difference between fall and spring planting is the “Short Day” factor, which usually is not addressed on a seed packet. If you are going to plant seed, you have to add 2 weeks to the numbers on the seed packet to allow for the cooler night temperatures and the shorter day lengths. According to her handout, if you want to sow spinach seeds for a fall harvest (i.e., before first frost), you have to add the 7 to 10 days for germination, 35 days to reach maturation, and 14 days for the Short Day factor for a total of 56 to 59 days. Therefore, the latest you can sow seeds is the beginning of September. The length of time would be shorter if you bought transplants from a nursery.

pak choi seedlings

pak choi seedlings

Another factor to keep in mind is the plant’s tolerance for cold temperatures, for example, beets, cauliflower, chard, Chinese cabbage, endive, kohlrabi, lettuce, mustard, peas, and rutabagas can survive light frosts. Broccoli, broccoli raab, Brussels sprouts, cabbages, collards, kale, radishes, spinach, and turnips can survive heavy frosts. Chicories, garlic, kale, leeks, multiplier onions, spinach, and shallots can stay in the ground over winter.

carrots in a fabric bag

carrots in a fabric bag

You can extend the season, which means to be able to harvest after frost, by protecting the plants from low temperatures with row covers, cold frames, hoop houses, and greenhouses. Libby has been gardening for many years and uses both row covers and cold frames to extend her harvest. She passed around her own row cover, made out of a synthetic fabric that allows light and water through and provides several degrees of protection. She also showed photos of her cold frames which she made with discarded windows. By growing greens in a cold frame she was able to harvest lettuce in February.

“Fall Vegetable Gardening” was free, courtesy of the Virginia Cooperative Extension and Master Gardeners of Northern Virginia, and will be offered again on Thursday, September 4, at Fairlington Community Center, 7:00 to 8:30 pm; and Saturday, September 20, 10:30 to noon at the Barrett Branch Library. Call (703) 228-6414 or e-mail mgarlalex@gmail.com to register in advance. http://www.mgnv.org