Sowing Seeds Indoors

Though most seeds are reliably started indoors, many types are easily started outdoors where they are to grow. The Park seed vegetable or flower Planting Guide, your seed packets, and the Park Seed Catalog Index will tell you which these are. Click here for easy directions on how to sow outdoors.

  • Planning
  • When to Sow
  • Seasonal Benchmarks
  • Preparing Seed Flats
  • Sowing Indoors, Medium Seed
  • Sowing Indoors, Tiny Seed
  • Sowing Indoors, Large Seed
  • Sowing in Park-Starts® or Park's Bio Dome Seed Starter

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Good timing in sowing seeds is a key to having transplants of the right size to set out in the right weather. Three important things to know are:

  1. The first and last expected frost dates for your area.
  2. The kind of weather liked best by the young plants of the types you're growing.
  3. The number of weeks from sowing to setting-out size.

When to Sow

You can ask your local county extension agent for the frost dates and other Seasonal Benchmarks for your area. You can also find this information in publications like the Farmer's Almanac, and on many Internet Websites by searching for "US Frost Free Dates." (We have provided a sample chart below for recording this information.) Some seeds need warm temperatures (about 70° F) or even warmer to germinate. Others need cool temperatures (about 55° F) or freezing to germinate well. Young plants may prefer a different temperature to grow on than the seed did to germinate. Remember that the germination temperatures we talk about refer to soil temperature. Indoors, soil temperatures will approximate the average of day and night temperature for the location. Outdoors, soil temperatures will be slightly below this average in spring and slightly above it in fall.

To find out when you ought to sow, first pick out the right date for setting out in your area; then count back the number of weeks to grow garden-size transplants.

Sort your seed packets into groups by their germination temperature requirements, so you will know which ones can be sown together.

Before you sow, pick some good locations (for more information about locations click here) around your house to set seed trays and to continue growing the seedlings after germination.

To find out how many seed trays to prepare, decide first how many plants of each kind you need, and sow twice that many seeds. For each 50 square inches of tray surface area, you may broadcast sow:

Up to 50 large seeds
Up to 100 small seeds
Up to 5150 tiny seeds

One or two varieties may be sown in each seed tray; just make sure to label them. You should sow rather thinly in the tray, allowing enough space so seedlings won't grow together and get overcrowded before they're ready to transplant (and to make transplanting easier). If you are starting seeds in individual cups, plugs, or cells, plant 2 seeds per cell.

Seasonal Benchmarks

Early Spring: Soil temperature is cool, but past the last hard freeze or heavy frost. May still have light frost.

Late Spring: Soil has begun to warm, and danger of frost is past.

Early Summer: Soil temperature and night temperatures have warmed.

Late Summer: Soil and night temperatures have begun to cool, but still before first frost.

Fall: Soil temperature has cooled and light frosts occur, but before first hard freeze or heavy frost. Ground is not frozen.

Winter: Soil temperature is very cold or soil is actually frozen. Hard freezes and heavy frosts; soil may freeze.


It may be helpful to use a planning paper like the example given below: (Example: Lexington, Va.)

Transplant Date in My Area: No. Weeks from sowing to garden size transplants: Date to Sow:
Ageratum Early Summer May 1 - 15 6 to 8 March 15

Preparing Seed Flats

Choose your sowing medium carefully. It should be porous and well-drained, but absorbent and soft as well. While finely textured humus or compost is fine, we have found Park's Grow Mix to be the ideal medium.

Most seeds are easy to start using Park's Grow Mix and Park's Seed Flats. Kits, such as the Park's Bio Dome Seed Starter or Park Starts®, allow you to skip the preparatory steps. (No's 1-4).

  1. For each flat to be filled, dip out four cups of grow mix and place in a plastic bag. Add 11/2 cups of water at room temperature.
  2. Close the top of the plastic bag tightly and squeeze the moistened grow mix to help it absorb the water thoroughly.
  3. Put the thoroughly moistened grow mix into a seed flat and pat it down, paying particular attention to the corners and edges, until the surface is level. Fill the flat to within 1/4 inch of the brim.
  4. Make shallow furrows one inch apart in the surface of the grow mix, using a pencil or your fingers; 1/4 inch deep for small seed or 1/8 inch deep for tiny seed. Large seed can just be poked into the medium without making a furrow.

Sowing Indoors, Medium Seed

  1. Shake or tap seed packet so that seeds go to the bottom of the packet. Cut the seed packet open across the marked line at the top. A clean cut makes smooth sowing easier.
  2. Pick up the packet with one hand, thumb on one side and fingers on the other. Press at the edges so that the packet stays open, and crease the packet at the center of the lower lip to make a trough. To sow seed evenly along the length of the furrow, hold packet level over one corner of the flat, close to the surface of the medium at the end of the first furrow. Move the packet slowly along the furrow, while tapping the packet lightly with a pencil or your finger. A few seeds should roll out into the furrow with each tap. If too many seeds fall too close together, simply separate them with the point of the pencil. If you are doing this for the first time, it may pay to practice sowing over a creased piece of paper first, to see if you are sowing your seeds the proper distance apart.
  3. To cover the seeds, pinch the furrows closed. A good rule of thumb is to make sure the seeds are covered to twice their thickness.
    NOTE: Seeds that need light to germinate should not be covered. Your seed packet will tell you if this is the case.
  4. To water the flat, place it in a pan of water at room temperature (cold water can slow germination), until the top of the medium is very moist. Bottom watering in this manner helps to prevent seeds being washed away by the force of sprayed water.
  5. Cover the planted flat with a sheet of clear plastic wrap (such as is used to cover food dishes) or enclose it in a clear plastic bag. Make sure plastic does not touch surface of sowing medium. Place flat where the seeds are to germinate.

Sowing Indoors, Tiny Seed

  1. Prepare the flats as previously described... with a pencil, press shallow furrows one inch apart parallel to the long side of the flat.
  2. For extra protection and easier handling, we package tiny seeds specially in a see-through glassine inner envelope, which you will find tucked inside our regular PARKSPAK®. Remove the glassine envelope from the PARKSPAK®. Handle it gently by the edges, as some tiny seeds can be easily crushed or broken. Hold the glassine envelope as shown in the illustration below, and tap the end with your fingernail until you can see the seed inside collect along the side crease of the envelope. Then snip off the end with scissors.
  3. Press the edges lightly between your fingers to hold open the mouth of the envelope. Sow seeds thinly by tapping the glassine gently with your finger. Seed should roll along the crease and out of the envelope in a single thin line.
  4. Because tiny seeds may be too small to break through a layer of germinating medium, they should not be covered with medium. This also applies to seeds that require light for germination (this fact is noted on the seed packet).
    Sow seeds into the rows, but DO NOT COVER THE SEEDS. Instead, cover the flat with a sheet of clear plastic, or enclose in a clear plastic bag.
  5. Water from the bottom to prevent seeds from being washed under the medium. Many tiny seeds need warmth to germinate (this fact is noted on the packet). Check the flats every day for proper moisture, watering only as much as needed to keep the surface moist, and making sure to water from the bottom.
  6. Keep the flat out of direct sunlight until the seeds begin sprouting, then remove the plastic covering. Move to filtered sunlight on a windowsill. Or place under a growing lamp, as soon as the seedlings appear.

Sow Small Seeds

Sowing Indoors, Large Seed

  1. Hold the top end of the packet between thumb and forefinger, shake seed to bottom end of packet, and cut or tear off the top of the packet.
  2. Pour the seeds out into your hand; use your finger or a pencil to poke each seed 1/4 inch deep into the prepared grow mix in the flat. Space 1 inch apart in rows 1 inch apart.
  3. Sprinkle dry Park's Grow Mix evenly over the seed if cover is required (see packet instructions). Seed should be covered to twice its own thickness. Fast germinating large seed should not be covered with plastic; those that germinate slowly do benefit from a plastic cover, applied so it does not touch surface of growing medium.
  4. To bottom-water the seed flat, place it in a pan of water at room temperature until the surface of the medium is thoroughly moist.
  5. Place flat where seed is to germinate.
  6. As soon as seedlings emerge, remove plastic covering (if used) and move flat to brighter light.

Sowing in Park-Starts® or Park's Bio Dome Seed Starter

Park StartsPark-Starts® and Park's Bio Dome Seed Starters will enable you to grow strong, healthy seedlings with minimum effort. Each Park-Starts Styrofoam block contains 18 individual pre-moistened plugs. The Bio Dome Styrofoam blocks come in 60, 40, or 18 cell sizes and the Double Bio Dome will hold two of the blocks.

Park's Bio Dome Seed StarterAs the name indicates, the Bio Domes have a convenient cover furnished with the unit. Each plug has been pre-dibbled so that a hole is already present to accept the seed. Just drop one or two seeds into each hole, place the unit in a favorable location, keep moist with a weak fertilizer solution, and wait for the plants to emerge. The Styrofoam blocks from either unit can be saved and refilled with new plugs year after year.

The holes in the plugs need not be covered over after sowing. Consult your seed packet for special instructions.

  1. Remove the Park-Start or Bio Dome Styrofoam blocks from the plastic wrap, keeping upright so that the plugs do not fall out. The plugs are ready to sow as they are!
  2. For most seed types, place two seeds into the pre-dibbled hole at the top of each plug. Tiny seeds should be sown on the surface of the plug, not in the hole. Seeds do not need covering in the Park-Starts or Bio Dome plugs. Each plug provides the optimum environment for germination.
  3. Place the germination units in a favorable location as indicated on the seed packet.
  4. Mix a weak fertilizer solution, following directions on the free fertilizer packet included with your Park-Starts or Park's Bio Dome Seed Starter shipment.
  5. To moisten the plugs it is best to soak them from the bottom. This can easily be done by putting the fertilizer solution into the under trays provided and floating the Styrofoam blocks in the solution. It is not possible to overwater by this method. Alternatively, the plugs may be lightly sprinkled with the solution, taking care so that the seed is not dislodged.
  6. Place the dome on the Bio Dome to maintain the humidity around the planted plugs. The Park-Starts may be placed into a plastic bag to accomplish the same effect. Keep moist with the fertilizer solution until the seedlings emerge. Again the blocks may be floated in the fertilizer solution. Because of their composition, the plugs retain just the right amount of water. Less frequent watering may be needed and there is no danger of overwatering as with some other germination methods.
  7. When you see that germination has started, open the vents on the Bio Dome or if the Park-Starts were put into a plastic bag, cut a few slits in the bag to give some ventilation. After the seedlings have emerged, remove the dome or plastic bag and provide more light. Water as often as needed to keep the plugs moist, using the fertilizer solution. Once a week gently water overhead with plain water and then continue to use the fertilizer solution.
  8. If you have double-sown, keep only the stronger seedling in each plug. Remove the other seedling by cutting the stem at the top of the plug with sharp scissors.
  9. Increase the light levels to prevent the seedlings from stretching and producing a weak plant. Brighter light will help keep the seedling short and stout.
  10. Transplant seedlings, plug and all, when the first or second true leaves appear. To remove the plug from the block, poke out from the bottom. Plant where the plants are to grow and give proper care mentioned else where in this booklet.
  11. If weather or timing delays your transplanting, often the roots will emerge from the bottom of the plugs. Prop up the blocks to allow some air space beneath them, until you are able to transplant but don't allow the plugs to dry. This builds a stronger root system within the plug.

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