How to Start Vegetable Seeds

I love planting seeds, but that wasn’t always the case. I remember the feeling of planting my first few seeds and thinking, “That’s it? There is no way these are going to grow.”

With a few years of practice, now I have confidence while planting seeds. So in this article, I’ll share our easy method for planting vegetable seeds, both indoors and outdoors. The goal is to help you feel comfortable when you plant your seeds this year, rather than worried and uncertain.

Various seedlings sprouted under grow lights

Reasons To Start From Seed

I assume you already plan to, but if you need more reasons to grow from seed, here are some great ones:

  • Starting seeds is (usually) cheaper. If you buy pre-started plants in spring, it definitely takes some of the work out of the process. However, the larger your garden, the more economical it becomes to start from seed.
  • You’ll have a better selection. Each year, we get more and more excited to shop for new seed varieties. There are so many different varieties of virtually everything. From dark red carrots, to purple peppers, to striped tomatoes, you can grow some truly unique cultivars right in your back yard!
  • The plants will be better quality. Nursery plants are usually beautiful, but this can come at a cost. Overgrown plants are often root bound, meaning that they have outgrown their pots and are overdue for transplanting. If you do shop for pre-started plants, get them early in the season and look for smaller plants with less developed roots.
  • It is more rewarding. I can’t explain just how satisfying it is to harvest your first seed-grown veggie from the garden. Whether it is a small sugar snap pea or a few lettuce leaves, the process is so fulfilling!

If you are brand new to gardening, I recommend starting some seeds, and buying some nursery plants. Seed starting is fun, but it is more important that your first year growing brings you some success, so try both!


Indoors or Outdoors?

The first thought you may have is whether to plant your seeds indoors or outdoors. Some vegetables, like tomatoes and peppers, require a long growing season. As a result, most gardeners need to plant the seeds indoors in the late winter.

Other veggies are fast-growing and cold-tolerant, and are better started directly in the outdoor garden soil. Whether you start indoors or outdoors will depend largely on two things: What you are growing, and your climate.

Start Seeds IndoorsStart Seeds Outdoors
BroccoliBeets
Brussels sproutsBeans
CabbagesCorn
CauliflowerCarrots
EggplantCucumbers
PeppersKale (or indoors)
TomatoesLettuce (or indoors)
Onions (sets)
Peas
Potatoes
Radishes
Squash

There are many vegetables not included here that you may be planning to grow. Follow the seed packet guidelines for when and where to plant your seeds.

Pak Choi seedlings sprouting

Climate

Another factor to consider is your climate. If you are lucky enough to live in a warm climate that does not experience freezing weather, you will have more flexibility. For example, you may be able to sow your tomato and pepper seeds outdoors rather than starting inside.

However, for many gardeners, planting will be based on when the weather begins to warm up. As the ground thaws, different vegetables can be planted along the way to spring and summer.


When To Plant Seeds

Next, consider the timing for planting your vegetables. Peppers are some of the earliest to be planted, about 6-8 weeks before the last frost. Carrots are typically sowed outdoors a couple weeks before the last frost. Squash and melons are usually planted directly outside after the ground has fully thawed.

So clearly, your last frost date is an important thing to know. If you live in Alaska, you’ll have to plant later in the year. If you live in sunny California, you’ll be able to start your seeds much earlier. I’ll cover more on timing for specific crops in the section below (skip now).

Find your average last frost date here.


Ideal Seed Starting Conditions

When it comes to germinating seeds, they can be stubborn. All seeds will have an ideal set of conditions for the fastest germination. The most important factors that you can control are the soil medium, temperature, and moisture.

Soil Medium

Young seedlings often perform best in a seed starting mix rather than traditional potting soil. Seed starter mixes are specifically formulated to have a lightweight makeup with high moisture retention.

You can use seed starter mix for starting indoors, but it can also be useful for outdoor sowing. Some seeds are tiny, and can easily become lost or washed away in outdoor garden bed soil.

Swiss chard seedling sprouts
Swiss chard seedlings. Sprouted just 3 days after planting.

If your garden soil is rough with woodchips and other large pieces, put down a thin layer of seed starter mix to provide a smoother surface for seed starting.

While seed starting mix is ideal, we have also started plenty of seeds in normal potting soil, garden soil, and even without soil at all. No need to overcomplicate it if you want to keep things simple.

Temperature

Temperature is one of the most important elements you can control during seed starting. Some crops, such as peppers, prefer warmth to initiate germination. Others like cool temperatures to germinate, and will not sprout well in warmth.

If you need warmer temperatures, try using a thermometer and testing different areas of your home. For example, above the fridge is a classic technique to get a few extra degrees. If you plan to start many hot peppers, a seed heating mat may be a worthwhile investment.

For cooler temperatures, outdoor sowing comes in handy. Carrots, lettuce, peas, and kale all prefer cool temperatures, and it is best to sow them directly outside when the temperatures are around 65°F. As a result, most of these crops are the first to harvest.

To summarize, use temperature to get your seeds to sprout faster and more consistently. Research exactly what it is you are growing to find the ideal soil temperature range.

Moisture

Lastly, moisture is required to start seeds. In fact, with just moisture, many seeds will sprout, even without light or soil. To keep seeds moist, I suggest doing two things:

  • Use a humidity dome. You can buy purpose built humidity domes to go with your seed starting trays. In fact, most trays come with one included. You can also use something like a plastic baggy or plastic wrap to create a makeshift humidity dome.
  • Spritz the soil regularly. Once you plant your seeds, check on them at least once per day to see if the surface has dried out. Keep it constantly moist by spritzing with water.
Spritzing seed starting mix with water
Spritzing seed starting mix with water to keep seeds moist during germination.

Important: Never let your seeds dry out once you have started germinating! This can halt the germination process, and potentially ruin your plants before they even sprout.

Fungus Issues

One of the most common issues faced when starting vegetable seeds is mold growth on the soil’s surface. Keeping soil in a humid, moist environment encourages fungal growth, especially in nutrient-rich soil.

Tip: Use cinnamon to suppress mold growth. Sprinkle a light layer of cinnamon on the soil’s surface to reduce fungal growth and spread.

Cinnamon on soil to reduce mold growth
Cinnamon sprinkled on soil’s surface to suppress mold growth.

How Deep To Plant Seeds

Deciding how deep to plant your seeds can be stressful.

Thankfully, they did, and since then I have learned to trust in the seeds. I now have a confidence when planting seeds. Seeds have one goal, and that is to grow! Have faith that they will succeed.

So, how deep? As a rule, plant vegetable seeds at a depth 2-3 times their width. For example, tomato seeds are about 1/8 inch wide, so they are best planted about 1/4 inch deep. Green beans are much thicker, and can be planted up to 1 inch deep.

Other seeds are extremely small, and shouldn’t be covered at all. For example, strawberry seeds are very small and can just be pressed into the surface of the soil for planting. They still need to be kept moist, so spritzing is critical!

There are some exceptions, for example when a seed requires light to germinate. Lettuce needs some light to sprout, so just cover them with a light dusting of soil.


Starting Seeds For…

With all of the basic rules for starting vegetable seeds, I want to give a brief guide to planting common vegetables and fruits. Remember, your climate will impact exactly when to plant, so figure out your last frost date above.

Beets. Direct sow beet seeds outdoors as soon as the soil has thawed. Plant beet seeds about 1/2 inch deep every 2-3 inches in rows. Beets are cold hardy and do not like temperatures above 75°F. For a fall harvest, plant seeds again about 6 weeks prior to your first frost.

Beans. Sow outdoors as soon as the soil is workable, or right around your last frost date. Plant seeds about 1 inch deep, every 2-6 inches (depending on whether they are bush or pole beans) in rows.

Carrots. Carrots don’t transplant well, so always plant carrot seeds outdoors as early as 3 weeks prior to the last frost date. Sprinkle seeds into a 1/4 inch deep trench and cover lightly with the soil. Keep the seeds moist by covering with mulch or a wooden board – this helps avoid the seeds shifting during germination. Once carrots sprout, thin them to one plant every 2-3 inches depending on the variety.

Cucumbers. Cucumbers can be started indoors for an earlier harvest, but I find it much easier to plant directly outdoors. Sow cucumber seeds outside about 2-3 weeks after the last frost date. There should be no risk of cold weather, so don’t plant too early! Plant seeds 1/2 inch deep in well-draining soil. Some cucumbers like to climb, so be sure to provide a trellis to save garden space.

Garlic. In cold climates, hardneck garlic is the preferred type. It requires a cold period to properly form a new bulb. Buy seed garlic (not actual seeds, but rather cloves), and plant it in late fall. This is typically in October or November, or about 2-3 weeks before the first frost date. Plant garlic by pushing 2-3 inch deep holes into the soil about 4 inches apart and drop the cloves in, root-end down. Cover them with soil and water. Cover the planted garlic with a mulch to retain moisture and warmth. By next July, you should be harvesting your garlic!

Kale. Many kale varieties are cold hardy, so plant seeds directly outdoors 2-3 weeks prior to the last frost. You can also start indoors 3-4 weeks before the last frost and transplant outdoors when the soil is workable. Kale seeds can germinate in temperatures as low as 45°F. Some plants are tolerant of some heat, so seek these out if you want to harvest kale into the hot summer months. For a fall and winter harvest, plant kale about 8 weeks before the first frost.

Lettuce. For the earliest harvest, plant lettuce seeds indoors 4-6 weeks prior to the last frost and transplant outdoors when the soil can be worked. You can also direct-sow lettuce seeds outdoors as soon as the soil is thawed. Lettuce seeds require some light to germinate, so only lightly cover them with soil. Lettuce prefers cool weather, and once it warms up the plants will go to seed (bolt). At this point, it can be removed from the garden to make space for another crop.

Onions. While onions can be started from seed, I always recommend using sets instead. Sets are essentially just a tiny onion that you plant like a seed. This will grow into a much larger onion that can be harvested later in the season. Plant onion sets when the weather is still cool, a week or two after the last frost date. Plant sets about 1 inch deep about about 5-6 inches apart, covering loosely with soil.

Peppers. Young peppers grow very slowly, so early germination indoors is required for cool climates. Plant pepper seeds indoors 4-6 weeks before the last frost date. Pepper seeds like warm temperatures to germinate, between 80-90°F is ideal (a seed heating mat will help). Move peppers outdoors once outdoor temperatures are consistently above 55°F.

Potatoes. You can start potatoes from an actual seed, but again I prefer using seed potatoes (small young potatoes intended for growing a new plant). Plant seed potatoes outdoors about 2 weeks prior to the last frost, or when the soil is workable. True seeds should be started indoors about 6-8 weeks prior to the last frost.

Radishes. Radishes are cool weather crops, and are often one of the first to produce. Sow radish seeds outdoors when the weather is still cool, right around your last frost date. Plant radish seeds about 1/4 inch deep in rows, and thin seedlings to be 2 inches apart. Remember to harvest your radishes as soon as they are ready to avoid a bitter, woody root. Plant again at the end of summer when the temperatures begin to drop for a fall harvest.

Spinach. Most spinaches love cool weather. Sow seeds directly outside as soon as the ground begins to thaw, between 4-6 weeks prior to the last frost. Plant spinach seeds about 1/2″ deep and thin plants to one per 6-8 inches, depending on the variety. Plant new seeds every week for staggered harvests, and again in late summer for fall harvests.

Tomatoes. Like peppers, tomato seeds should be started indoors. Start tomato seeds indoors 4-6 weeks before the last frost date. Tomatoes can grow quickly, so be sure not to plant too early! Transplant into larger containers while still indoors if necessary, and move the plants outside once the overnight temperatures are above 55°F.

Tomato seedlings sprouting in seed cells.
Tomato seedlings sprouting.

I hope you find this article useful for starting vegetable seeds indoors and outdoors. It is always helpful to plan ahead, so draw a sketch of your garden during the winter and stick to the plan!

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