When Should You Start Your Seeds Indoors?

When you first start gardening, it can be tricky to know when you should start seeds indoors and when you should directly sow them outdoors. Today we are giving you a breakdown of what techniques should be used with the most common garden seeds. Ultimately the best technique will depend on how long your growing season is. If you live in a tropical growing climate, chances are you can direct sow most of your seeds. Those of us blessed to live in regions with shorter growing seasons get to strategize and plan for our desired results.

The big questions are, what should you directly sow? And what needs to be started indoors ahead of time? While there are some general guidelines, you will likely discover your own personal preferences for your location. We encourage you to always keep a growing journal to record the progress of your garden. Take note of anything you would like to do differently in the coming year, varieties you would like to grow again, and weather patterns or anomalies you observe.

Many days to maturity are presented as a range because local weather or your growing practices can influence how quickly a plant produces fruit. You can locate the days to maturity on the seed packet or seed product page. If a specific variety takes longer than the recorded days to maturity, plan to start that seed sooner the following year. Plants that are not directly sown, such as tomatoes and peppers, will list the days to maturity as the number of days to maturity after transplanting. They will require an additional 6-8 weeks of growth indoors.

Plants to Start Growing Indoors:

• Flowers - Most flowers do well when started indoors and later transplanted. Try growing your flowers from seed this year!
• For the best looking hanging baskets, try our Bloom Master Water Retention Kits. They are specially designed for retaining water during the hot summer months. You can pair your favorite flowers with these baskets for a full, luscious look. You will have too many blooms to even see the basket structure.

These traditional summer vegetables are a hit year after year! Plan ahead as these take some extra time to mature than other common vegetables.

• Broccoli
• Brussels Sprouts
• Cabbage
• Cauliflower
• Celery
• Eggplant
• Peppers
• Tomatoes

While its true that most cool-season vegetables can be directly sown, you can still benefit from starting them ahead of time. We suggest giving your leafy greens a head start as they adapt well to the cool spring soil temperatures when transplanted.

• Lettuce
• Spinach

These plants are not ideal for starting indoors, however many regions do not have growing seasons long enough for these vegetables to reach maturity when directly sown. When transplanting these starts, be extremely gentle and avoid damaging the root systems as much as possible.

• Beans
• Cucumbers
• Melons
• Pumpkins
• Summer Squash
• Winter Squash

Plants to Direct Sow:

• Wildflowers are some of the easiest flowers to plant because they often require little maintenance compared to others. Not only can wildflowers be planted in the spring, they may also be sown in the fall. Learn more about cold stratification and how it can improve wildflower germination rates when planted in the fall or spring months.

Because these cool-season vegetables can adapt to the cooler soils, you don't have to start them ahead of time. In addition to their adaptablility, they are also quick to grow and mature to their harvesting stage.

• Lettuce
• Peas
• Radishes
• Spinach

Root vegetables shouldn't be started ahead of time as damage to the root structure can stunt growth. For the best harvesting results, be sure to check your soil health. A balanced loam soil rich in organic matter is ideal for strong root development.

• Carrots
• Turnips
• Beets

While many of these summer and fall vegetables are commonly started indoors, they prefer to be directly sown if your growing season allows enough time. Corn especially does not like to be transplanted.

• Corn
• Beans
• Cucumbers
• Melons
• Pumpkins
• Winter Squash
• Summer Squash

When Should You Grow Your Indoor Seed Starts?

Most seeds need to be started 6-8 weeks before your last spring frost date. Some flowers can require considerably more time. Be sure to check your garden plans to get everything ready in time for your spring planting. The first 2 weeks will be spent on the germination process. Following germination, you will want to allow enough time for several true leaves to develop. The first 2-4 leaves you see are called cotyledons. These leaves form from the stored nutrients in the seed. True leaves come after and rely on nutrients taken up from their surrounding environment. Generally, 4-6 weeks is enough time to develop a strong enough start to survive being transferred outdoors. Always harden off your seedlings before transplanting.

If you aren’t sure what your growing zone is or the last frost date, locate that information here. Your growing hardiness zone will help you select plant varieties known to perform best in your growing climate. Your last spring frost date is specific to your area. It may be different for people within the same hardiness zone depending on variations in topography such as mountains, elevation, valleys, etc. For more advice on the best time to plant in your area, contact your local extension office. Other helpful gardening advice can be found in local university resources. Explore the garden pages for universities in your state and those with similar growing conditions as listed on our USDA Hardiness Zones by State page.

Select your indoor planting date by identifying when your last spring frost takes place. Then, count back 6-8 weeks. This will tell you your planting time. In your garden journal/tracker, take note of the expected germination and transplant dates. Add in any maintenance or plant care that should occur. This will prevent important care steps from being forgotten or overlooked, like pruning, fertilizing, or changing light requirements. You can find more growing information on our How to Start Seeds Indoors article.

When Should You Transplant Your Seed Starts?

The last potential frost date for your growing zone marks the first opportunity you have to start planting. However, more conditions should be taken into account. Plants generally do not like to be in soils cooler than 50 F. If your air temperatures are lower than 42-50F, it is likely still too cold for you to plant if you are not experiencing sunny weather regularly. On cold winter days, soil temperatures are usually 1-8F cooler than the air. On sunny days they can be 10-40F higher. This is why you may see instructions to plant “when the soil is workable.” Summer vegetables such as tomatoes and peppers do best when soil temperatures are about 70 F. Protect young transplants by covering them during fluctuating spring temperature drops.

Other Resources:

• UMN Extension - Seed Starting