I had the opportunity to speak on vegetable gardening basics recently at a local home and garden show. The difference between cool and warm season veggies was one of the topics the show organizers asked me to address. As a long time gardener I kind of thought that was an odd request, I mean we all know the difference between cool and warm season veggies, right? But this is an important topic for any new gardener to understand!
At the simplest level the difference between cool and warm season veggies is the time of year you grow them. Cool season veggies like the cooler weather of spring, fall and some times winter. Warm season veggies like the heat of the summer! But there is really a lot more to it, so let’s take a bit of time and talk about each type of veggie, the conditions they like and what veggies are considered cool season and what are warm season!
Cool Season Vegetables
As the name implies cool season veggies like cool temperatures. A general rule of thumb is that you want to plant your cool season veggies so that they mature before your day time temperatures exceed 80° Fahrenheit. Cool season veggies prefer temperatures between 55° and 75° F. Additionally cool season vegetable seeds will germinate with much lower soil temperatures. Seeds will come up with soil temps as low at 40°, but optimal soil temp for germination is around 70°F.
Cool season vegetables can handle much colder temperatures; they can even handle a little frost without any major damage. In fact the taste of crops like, kale, Brussels sprouts and kohlrabi actually improves with a little frost to “sweeten” them up!
Hot weather is the enemy of your cool season crops. Temperatures consistently over 80° will very quickly affect the quality of your cool season crops causing leafy veggies to go bitter and many others to bolt (send up flowers and set seeds). So plan accordingly, get your cool season veggies in early in the spring so they are done before the summer heat. For us here in zone 5b we target planting times between March 15th & April 30th so that the crops are mature no later than mid June. Your planting times will vary based on what hardiness zone you live in.
Keep in mind that cool season veggies can also be planted in the fall. Target planting dates will be in mid to late summer. Cool season veggies planted in mid summer for a fall harvest will need a little extra care during the hot times (extra water & maybe a shade cloth). The idea with late summer plantings is to have the plants starting to mature when the weather cools off in the fall. Keep in mind that the amount of sunlight is declining in the fall (as opposed to increasing in the spring) so your plants will mature slower in the fall. Plan on adding about 10 days to your growing time in the fall.
Here’s the list of Cool Season Crops
Lettuce Spinach Carrots
Swiss Chard Beets Radish
Turnips Chinese Greens Broccoli
Cabbage Kale Kohlrabi
Peas Cauliflower Green Onions
Leeks Scallions Mache
Most leafy greens
Warm Season Vegetables
These are the veggies of summer! Warm season vegetables grow best in the long hot days of the summer time. Cold weather actually shuts down the growth of warm season veggies. Frost will always severely damage or kill a warm season crop. For this reason we don’t plant our warm season veggies until later in the year when day time temperatures average between 65° and 95°. Additionally warm season crops need a minimum soil temperature of 65° to germinate and they prefer soil temps much warmer than that!
Planting times for warm season veggies are usually mid to late spring. For us in zone 5b that means early May is when we start planting and we are usually finished planting by late June. Some cool season veggies can tolerate a little bit of shade but warm season veggies love the sun and will not do well without 12 to 14 hours of daylight. So plant your warm season crops in the sunniest spots in your garden.
Watering and pests are also usually a much bigger concern with warm season vegetables. Having a great drip irrigation system will help you to be able to water your warm season veggies deeply! Mulching also helps hold in water and keep down weeds. Pests and other problems are also much more prevalent in the warm summer temperatures so be sure to keep a close eye on all your warm season crops and act quickly to eliminate any pests!
Having a good indoor seed starting set up, can help immensely with your warm season crops. You can get a huge head start on the season by planting your warm season crops early indoors and then transplanting your seedlings out to the garden later when the temperature have warmed. This is 100% necessary for plants like tomatoes, peppers, and many herbs. For other warm season crops like melons, cucumbers and squashes planting indoors can get you an extra 2 or 3 weeks but these seeds usually can also be planted directly in the garden and still be successful.
Here’s the list of warm season crops:
Corn Beans Tomatoes
Melons Potatoes Summer Squash
Cucumbers Eggplant Most Herbs
Onions Mustard Squashes
Pumpkins Peppers Sweet Potatoes
A few other things to know
It is possible to “cheat” a little bit with warm season crops. Cloches, hoop houses, cold frames and wall-o-waters are all great ways to get an early start on your warm season crops. Wall-o-waters will allow you to get your tomato plants in the garden up to two months before your last frost. This can really increase your harvests. Also a nice heavy fabric row cover used to protect warm season crops from frost in the fall can add up to a month to your harvest of tomatoes and other warm season crops.
There are some crops (both warm and cool season) that are more hardy than others. Many herbs will tolerate some pretty cool temperatures in the spring and fall. Corn holds up pretty well to cool temps and can be planted earlier than more tender crops like squashes and melons. Broccoli holds up better against the heat than most other cool season crops and cabbage around our place really isn’t even ready till mid July. So the rules I have laid out here do have a little flexibility.
In my opinion there are such things as COLD weather crops as well. Some of the cool weather crops end up being very hardy and with just a little protection from a simple hoop house or cold frame you can stretch your harvest well into the winter months. These plants include kale, spinach, Swiss chard, carrots, Mache and several other leafy greens. You can learn more about winter gardening here.
So there you have it! The difference between cool and warm season veggies! Now get growing!!