How to Plant Seeds Outside

Don’t let learning how to plant seeds outside intimidate you. It is an important skill to learn. There are many seeds that are best planted directly in the garden. Learning how to plant seeds outside correctly will help ensure seeds germinate and grow so you can enjoy them in your garden.

8 Tips for How to Plant Seeds Outside

1. Select the best seeds to grow in your garden

When selecting seeds: 

• Choose high-quality seeds from reputable seed companies. A few of my favorite seed companies are Botanical Interests, Renee’s Garden Seeds, Seeds Now, Baker Creek Seeds, and Native Seeds Search.
• Look for seed varieties that are adapted to your location. 
• Choose disease-resistant varieties if you have had issues with a disease in the past.

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2.  Plant seeds at the right time

Seeds require correct temperature, moisture, air, and light requirements in order to germinate.

Plant seeds at the right time and soil temperature for the best germination rate and healthy seedlings. I use this soil thermometer to measure the soil temperature before planting.

Use your local planting guide (this post will help you find one) and soil temperature (check it with a soil thermometer) to determine the best time to plant.

Seeds germinate best at optimal temperatures. Use this chart from Penn State Extension for basic soil temperature guidelines of when to plant.

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Vegetable Crop	Minimum (°F)	Optimum Range (°F)	Optimum (°F)	Maximum (°F)
Beet	40	50-85	85	85
Bean	60	60-85	80	95
Cabbage	40	45-95	85	100
Cauliflower	40	45-85	80	100
Celery	40	60-70	70	85
Chard	40	50-85	85	95
Cucumber	60	60-95	95	105
Eggplant *	60	75-90	85	95
Lettuce	35	40-80	75	85
Melons	60	75-95	90	100
Onion	35	50-95	75	95
Parsley	40	50-85	75	90
Pea	40	40-75	75	85
Pepper *	60	65-95	85	95
Pumpkin	60	70-90	90	100
Spinach	35	45-75	70	85
Squash	60	70-95	95	100
Sweet Corn	50	60-95	95	105
Tomato *	50	70-95	85	95

• = Does best when started indoors and planted as a transplant in the garden.

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3. Prepare the soil before planting seeds

A plant will reflect the quality of the soil. I use this soil mixture in all of my beds. Add compost to your garden beds each season. Have your soil tested regularly, and amend the soil as needed to adjust the pH or nutrient levels.

For seeds to germinate, the soil should be moist and fluffy. Compacted soil does not have the air necessary for germination. Use a sprinkler attachment to moisten the soil before planting seeds. 

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4. Plant seeds at the correct depth

As a general rule, plant seeds two times as deep as they are wide (not tall). Seeds may require light to germinate and should not be planted deeply but only lightly covered with soil. Follow seed packet directions for exact depth requirements. 

Planting all of the seeds (of the same type) at equal depths will ensure more even germination. Use a dibber to measure how deep to plant each seed. 

How to plant a seed:

• Pull back mulch (if using).
• Make an indentation with a dibber in the soil.
• Place seed in soil indentation.
• Lightly cover with soil.
• After planting, firm the soil a bit with your hand to ensure good seed-to-soil contact. 
• Replace mulch during hot weather to keep the soil moist.

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5. Follow plant spacing guidelines to give seeds enough room

Although seeds look small when you plant them, most will grow into large plants. It is important to give seeds enough room to grow. Overcrowded plants are more prone to pests and disease and must compete with each other for adequate light, air, moisture, and nutrients.

The back of the seed packet provides information about how far apart to plant the seeds. Follow the guidelines when you plant your seeds. 

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An overview of different methods for the spacing of seeds in vegetable gardens:  

Square foot gardening – A certain number of seeds (depending on the plant) are planted in each square. To learn more about square foot gardening, read this post.

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Row planting – Typical planting method. Plants are spaced within the row and then rows are spaced a certain distance apart. See seed packet for distances. Use string between two stakes to mark your row and plant seeds at the correct depth and spacing. 

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Bed planting – Intensive planting method for some leafy greens and root crops. Seeds are spread evenly or broadcast over the planting area.  

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Hill planting – Method that helps warm the soil in early spring. Mound soil for each foot to about 1 foot wide. Used for larger vegetables like melons, squash, and corn. Follow hill spacing and planting guidelines on seed packets.

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6. Do not let newly-planted seeds dry out

• Plant seeds in moist soil and lightly water them after planting to ensure good seed-to-soil contact.
• Once planted, seeds begin taking up moisture from the surrounding soil. The newly-planted seed expands with the added moisture and opens. 
• The root emerges first and begins absorbing moisture and growing, anchoring the plant into the soil. The shoot emerges next and begins its journey up through the soil. This newly-emerged plant is called a seedling. 
• As the seed opens and begins to grow, adequate moisture is critical. Once the seed opens up, if a seed dries out, it will stop growing and die.
• Frequent, light applications of water are best at this stage of development. Strong streams of water may disturb seedlings and disrupt the soil. 
• Keep newly-emerged seedlings moist, gradually lengthening the time between waterings as the roots deepen and grow. 

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7. Protect newly-planted seeds and seedlings from birds and frost

Use barrier methods such as tulle or cloches to prevent birds from eating planted seeds or damaging seedlings. Young seedlings are also tempting to in-ground pests like rollie-pollies. Use the tips in this blog post to help prevent pest damage. 

Pay attention to the weather and be prepared to cover newly-planted seedlings with frost cloth, cloches, or row covers if temperatures fall below freezing. 

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8. Thin seeds when true leaves appear

Thinning is a term that describes removing the extra sprouted seeds that were planted too closely together. Thin seedlings by removing the extra seedlings until the plants are at the desired spacing. 

The best time to thin seedlings is usually after the first set of “true leaves appears”.

The first leaves to emerge are the cotyledons or “seed leaves”. True leaves emerge next, and they unfurl above the seed leaves and look like smaller versions of the adult leaves.

How to thin seedlings: 

• Select the strongest seedling. Strong seedlings are compact with short (not leggy stems).
• Use small clean snips and cut the weaker seedlings off at dirt level. Do not pull out seedlings. Pulling may disrupt the roots of the seedlings you are leaving in place. 
• With some crops like carrots, you may want to do an initial thinning and then come back in and do a second thinning once the plants get a little bit larger. 

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Once you understand these guidelines for how to plant seeds outside, don’t be afraid to begin planting seeds in your garden. Do you still have questions about how to plant seeds outside? Ask me in the comments. 

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