You can plant any seed outdoors in the spring, but did you know that some species of garden plants prefer cooler temperatures?
If you are unsure of what you should start outdoors once your soil thaws in the spring, then I hope this article can help!
Cool Season Crops vs. Warm Season Crops
Begin by taking a look at your seed packages. Some species of plants are more suited to different types of growing temperatures. You may notice that some seed packages specify to plant outdoors and some say to start indoors 6-8 weeks prior to last frost. This is an indication of whether or not your plants are cool vs. warm season plants.
The spring and fall are considered cool seasons in the garden while the summer is considered the warm season. Growing cool season crops in the spring and fall means growing plants that are more suited to cooler temperatures and grow better before the blazing summer heat. All of these plants can withstand a light frost with some more hardy than others.
Warm season plants are frost-sensitive and can only be grown outdoors once overnight temperatures are above freezing. These plants cannot handle any type of frost whatsoever and must be protected if frost or near-zero temperatures are expected.
Cool Season Crops:
- Arugula
- Broccoli
- Brussels sprouts
- Cabbage
- Carrots
- Cauliflower
- Chives
- Cilantro
- Kale
- Kohlrabi
- Lettuce
- Mint
- Onion
- Oregano
- Parsley
- Peas
- Spinach
- Swiss chard
- Thyme
Warm Season Crops:
- Basil
- Beans
- Corn
- Cucumber
- Gourds
- Ground cherries
- Melons
- Peppers
- Pumpkins
- Squash
- Tomatoes
What Seeds Should I Plant Outdoors?
While you can plant any type of crop directly in the ground, with our shorter growing season you may want to get a head start on some of your warm season plants. This would mean starting your seeds indoors and planting them outside after the date of the last frost. You can read my article 10-Steps for Indoor Seed Starting for advice on starting warm season plants indoors.
I recommend cool season crops for your earliest outdoor seed sowing. Since cool season crops are well suited for lower daytime and nighttime temperatures, they will not be easily killed off with a frost.
The one exception to warm season plants that I make is corn. Corn cannot withstand frost and it is a “monocot” which means it grows a long taproot. This type of root makes it harder to transplant without damage. Corn grows best when it is planted directly in the ground after the date of last frost.
10 Steps to Planting Seeds Outdoors
Using the list of cool season crops above, here are my suggested steps to follow for successful outdoor seed planting. You can follow these steps for both spring (May/June) and fall (August/September) planting.
- Prepare your seeds – Begin by determining which seeds you wish to sow outdoors. Prepare some plant labels with the names of the plants you are sowing. I love using plastic plant labels with China markers. The markers write on all kinds of surfaces and don’t wash off with water. You can use rubbing alcohol with a cotton ball to wipe off your labels and reuse them from year to year.
- Make a plan for your garden – based on your growing space. Now that you know what you want to grow, you can determine where you want to plant your seeds. You can make a sketch of your garden like the example I provided in my article Preparing for the Growing Season. This gives you an idea of where to place your plants and how many you can fit in one space. You can follow the back of the seed package, or follow a framework like the Square Foot Gardening (SFG) guides that are available via the SFG Foundation. SFG produces a book that provides suggested plant spacing and companion planting. You could also follow some of the guides created by other gardeners such as this one. This is really just to give you a starting point from which to make your plan.
- Check your soil depth – If you are planting in early spring, you’ll want to go outside and begin checking your soil once daytime temperatures begin to consistently go above zero. This is when your soil will begin to thaw. Just for fun, I like to bring a ruler out with me to measure the depth of the frost from the top of the soil. I will begin planting once the top of the soil is thawed to at least 7-8″. Note that I plant in raised beds which will thaw quicker than in-ground gardens. You can learn more about the types of microclimates you may experience in your yard based on the design of your garden in my Gardening in Zone 4 article.
- Add nutrients – Now that you are ready to plant, you should amend your soil with nutrients. I like using worm castings, cattle or sheep manure, compost, fish emulsion, hen manure pellets, or other types of natural or organic nutrients. I prefer these over chemical nutrients as they contribute to soil health which leads to stronger plant roots and healthier plants. Healthier plants also mean stronger resistance to disease. Typically I will take a bag of manure and spread it about 2″ thick in my raised beds. I then lightly mix it into the top 4-6″ of soil careful not to overly disturb the soil. This is the part where you will want to have some gardening gloves on!
- Add labels and space your holes – Place a plant label where you are about to plant your seeds so you can mark the area and remember what and where you planted. Based on your plan for seed spacing, poke your holes at the appropriate spacing. Seed depth is generally 2x the diameter of the seed (ex: larger seeds, such as pumpkin, are planted deeper whereas smaller seeds, such as oregano, are planted closer to the surface).
- Begin planting your seeds – Shake some seeds into a small bowl and using a non-gloved hand (just for dexterity sake), place your seeds in the holes. Since I plant closer together I will drop one seed per hole and it’s ok if some don’t germinate as they are closer together. However, if you are spacing yours wider, you may want to include 2-3 seeds per hole. Also, if your seeds are from last year or a previous year, you may want to drop a couple more in each hole as germination success can reduce over time as the seeds age.
- Finish planting – Once all your seeds are in the holes, cover them up with the soil and gently pat down. You may wish to mark off the areas where you have planted with additional labels. The trick here is to not add more seeds to this area until you see what’s coming up!
- Add some water – Using a watering can, water the soil on and around the seeds. You will want to keep the soil moist but not soaked to ensure germination. If you are worried about multiple days of freezing temperatures after planting, cover your soil with cardboard to keep the soil warmer at the surface. Each plant needs a different soil temperature and amount of time under ideal conditions to germinate.
- Observe germination – As you notice your seeds germinating, you will need to remove any covers you had on your soil and allow the seedlings access to sunlight. If the forecast is calling for a hard frost (-4 C or colder) then consider covering them for the evening just to be safe. If the forecast is calling for a light frost (0 to -4 C) it may be ok to keep your seedlings uncovered. This all depends on your soil temperature and the stage of growth your seedlings are at. Seeds have evolved to germinate at the right temperatures and conditions so likely you won’t need to take any action, especially since you are working with cool season crops. If you are worried, you can always cover them but be sure to uncover them in the morning once temperatures have warmed a bit.
- Thinning and supporting your plants – You may wish to thin your seedlings if they are growing too close together. This ensures plants have enough space without competition from other plants. I will usually trim the extra seedlings at the base of the stem using scissors rather than pull them out. By cutting, you won’t disturb the roots of the seedlings nearby. Other people like to pull seedlings and re-plant them elsewhere. This is your choice but know that your plants may get damaged if their roots are intertwined. Continue watering and once your plants are about 4-6″ tall, you can begin to place any supportive structures around them (such as trellises for peas, for example).
Alternative Strategies
The ten steps listed above are ones that have consistently worked well for me personally in my home garden.
There are many strategies, methods, and forms of advice around planting outdoors. You may wish to read other articles that cover some of these ideas in more depth.
As mentioned above, I garden in raised beds and my methods may be different from yours. If you are planting directly in the ground rather than in a raised bed or garden box, you may find that tweaking these ideas above works better for you. Perhaps you are mechanically seeding, or maybe you have a large plot that you like to plant in rows. Please share your methods in the comments below, I would love to learn from you!
Gardening and starting seeds does not need to be an exact science – much of it comes down to experimentation, experience, and intuition. If something has worked well for you in the past, excellent! You can then come to rely on your own methods through continuous practice and learning.
If you are new to gardening or new to planting seeds outdoors, I hope that this guide gives you at least a starting point to feel confident.
I wish you much success and enjoyment in your home garden!
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