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FAQs about Starting Vegetable Seeds Indoors

What is the advantage of starting vegetables from seed?

Choosing to start vegetable plants from seeds allows gardeners the freedom to try varieties that are not readily available as transplants, such as heirloom varieties. It also allows gardeners to get transplants ready and, in the ground, quicker than they might be found in the garden center. Not only does starting transplants from seed save time, it also saves money. For example, ten heirloom tomato plants started from seed is much cheaper than buying those tomato plants from a retail store.

What species are best to start from seed and transplant well?

Not all species are created equal when it comes to starting with transplants versus direct seeding. Warm-season crops like eggplants, peppers, and tomatoes easily survive transplanting. Cucurbits such as cucumbers, melons, pumpkins, and squash work well as a transplant but require extra care to prevent disturbing the roots during transplanting. Ideally cucurbits transplant best when very small, after the first true leaves emerge. Beans, beets, carrots, and corn are typically not transplanted successfully and should be directly sown into the soil.

When do seed need to be started?

Popular warm season vegetables should be sown 4 to 8 weeks before planting outside. Germination time varies by crop species.

Plant Week to seed before last frost
Cucumber 4 or less
Eggplant 8
Muckmelon 4 or less
Pepper 8
Squash 4 or less
Tomato 6
Watermelon 6

What supplies are needed to sow the seed?

Start with reliable seed from a reputable source. A reputable source will supply high quality, weed-free seeds. Seeds can be started in just about any container that is clean, has good drainage, and is at least 2-inches deep. For example, plastic flats with drainage holes and cell pack inserts can be purchased at farm and garden supply stores. Do not use regular garden soil to start the seeds. Garden soil is heavy and potentially filled with weed seeds and pathogens. A soilless potting mix that consists of sphagnum peat moss, perlite, and vermiculite will work best. A general-purpose soilless mix works well to start seeds; avoid potting mixes with large particles like bark or wood chips. A soilless growing mix is superior to garden soil because it is sterile, lightweight, holds water well, and allows excess water to drain easily.

Start with reliable seed from a reputable source

Start with reliable seed from a reputable source.
Millie Davenport, ©2019 HGIC, Clemson Extension

A general-purpose soilless mix works well to start seeds.

A general-purpose soilless mix works well to start seeds.
Millie Davenport, ©2019 HGIC, Clemson Extension

If using cell packs, two to three seeds can be used per cell and thinned later to maintain one seedling per cell.

If using cell packs, two to three seeds can be used per cell and thinned later to maintain one seedling per cell.
Millie Davenport, ©2019 HGIC, Clemson Extension

At planting time, the soilless mix should be damp like a sponge. Sow seed at a depth two times the diameter of the seed. Afterwards, gently firm the media to create good seed contact with the potting soil. If using cell packs, two to three seeds can be used per cell and thinned later to maintain one seedling per cell.

What growing conditions are necessary?

Typically, indoor lighting from a window is not sufficient and will produce “leggy” seedlings that have a tendency to lean toward the light source.

Typically, indoor lighting from a window is not sufficient and will produce “leggy” seedlings that have a tendency to lean toward the light source.
Millie Davenport, ©2019 HGIC, Clemson Extension

It requires a high light level to produce healthy seedlings. Typically, indoor lighting from a window is not sufficient and will produce “leggy” seedlings that have a tendency to lean toward the light source. One of the easiest ways to avoid this problem is to use fluorescent light bulbs to grow seedlings. The lights should be placed 2 to 4 inches above the seedlings and raised as the seedlings grow over time. Lights should be left on 12 to 16 hours per day. A timer can be used to automatically turn these off for a period of time each evening.

In general, a soil temperature of 65° to 75°F is ideal for germination to occur. The soilless mix can be warmed easily by draping a piece of clear plastic over the frame supporting the light fixture. Do not allow the plastic to come in contact with the light fixture.

Can I plant them when the weather warms up?

Young seedlings grown indoors are too tender to be placed directly in the ground. To prevent damage, they should be gradually acclimated to the outside environment. Two weeks before planting the garden, place the transplants in a protected area with part sun and then gradually expose them to more sunlight each day. Also reduce the amount of water but do not allow the plants to wilt. Bring the plants in each evening until the nighttime temperature stays at or above 50°F. Avoid exposing tender seedlings to wind or temperatures below 45°F.

What are other tips that are critical to know when starting seed?

  • Keep the soil consistently moist during the germination process. If the growing media is allowed to dry out, the seed will no longer be viable.
  • The flat can be covered with clear plastic wrap or a plastic bag to increase humidity during germination. The plastic should not come in contact with the soilless media, and it should be removed as soon as the seedlings emerge.
  • When the first set of true leaves emerge, the seedlings should be fertilized at every other watering with a liquid starter fertilizer.

For more information see, HGIC 1259, Starting Seeds Indoors; and HGIC 1256, Planning a Garden.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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