Starting Flowers from Seed

The basic best practices of seed starting apply across all seed crops, but there are also some specific tips and techniques that can help assure success in starting flower crops from seed. In this article we will provide detailed guidance on starting 9 popular cut-flower crops from seed.

Why Start Flower Seeds Indoors?

There are several benefits to growing your own flower seedlings instead of buying starts. Starting your own flower seeds gives you access to a wider selection of varieties and more control over the color palette of your cuts. When compared to direct seeding, starting seeds indoors is a favorable option for flower crops with slow germination and longer seedling development.

Seed Starting Best Practices

We encourage you to review our Guidelines for Starting Seeds Indoors for a thorough review of essential best practices applicable to all seed crops, including flowers. Then, read on for more flower-specific information.

A Note About Pelleted Seeds

Pelleting is a seed enhancement that coats the seeds with inert substances that render them uniform in size and shape. Pelleting is a process often applied to very small seeds, as the pellet coating serves to improve seed visibility, handling, sowing accuracy and efficiency, thereby reducing seed waste and the need for thinning. Examples of flower crops that Johnny’s offers in pelleted seed include: campanula, dianthus, digitalis, lisianthus, and snapdragon. While pelleting offers many advantages, the process and nature of pelleting may shorten the shelf life of the seed. We recommend using pelleted seed within one year of purchase. If you need to store pelleted seeds until planting, protect them from heat and humidity by placing them in a cool, dark, dry place. If you prefer to store your seed in the refrigerator, place the seed in an air-tight container to protect it from fluctuations in humidity.

Reading Your Flower Seed Packet

Essential germination conditions and planting instructions are listed on each packet and online in our flower key growing information pages. As you review these growing resources, it may be helpful to note the following.

Front of the Seed Packet

• For all flower crops, we list days to maturity as the number of days from seeding date (regardless of whether you are direct seeding or transplanting).
  
  For flowers, that is the estimated length of time from seeding to harvest for cut flowers. We consider maturity when 25-50% of the plot is flowering. The days to maturity that we list in our growing instructions is based on multi-year data collection from our trial fields.
• You will also be able to see the germination test results on the seed packet; this number sets the baseline for what you can expect for seed germination under appropriate conditions.

Back of the Seed Packet

• In the culture, we will note if transplanting or direct seeding is preferred.
• We provide the estimated time in trays from seedling to transplant. This is a range, as the time can vary with environmental conditions and the tray cell size used.
• We provide the expected number of days to germination and the optimum temperature range for germination. If grown outside of the recommended temperature range, seeds may still germinate but germination may be slower or at a lower percentage than expected.
• For most flower crops, the recommended temperature for growing on (growth after initial seed germination) is lower than the recommended temperature for germination. Adjust your conditions appropriately.

Breaking Seed Dormancy

Some crops need some extra encouragement to break dormancy and germinate. Generally, these crops need some special care in regards to light or temperature control:

1. Light (or Darkness Requirements: Some flower crops require light or darkness for germination. We note these requirements in the growing instructions. Requires light: For these crops, make sure the seeds have some exposure to light and are not in complete darkness. Place trays under grow lights until the seeds germinate. Even for crops that require light to germinate, we still cover the seeds lightly with vermiculite to help retain moisture. Some flower crops that require light to germinate are: ageratum, alyssum, rudbeckia, dusty miller, matricaria, and lisianthus.
   Requires darkness: Some flower crops require darkness for germination. Either cover the seed completely with potting mix or keep seedling trays in dark conditions until germination occurs. Examples of flower crops that require darkness include phlox and nasturtium.
2. Cold Stratification
   Cold stratification is the process of exposing seeds to cold temperatures for a period of time in order to break seed dormancy and promote germination. Most flower crops, especially annuals, do not require cold stratification. For crops where cold stratification is necessary, we indicate the ideal temperature range and length of time for cold exposure. For example, the growing instructions for Rudbeckia triloba recommend prechilling the seeds in the refrigerator for 30 days prior to seeding.

Soaking Seeds

Soaking seeds before planting is not necessary for most crops. For those crops, like sweet peas, where it can be helpful, we include soaking recommendations in the growing instructions.

Tray Selection for Flower Crops

There are many options for starting seeds, including soil blocks, biodegradable pots, and plastic pots/trays. To learn more about the pros and cons of these different methods, review our article Three Systems for Indoor Seed Starting.

At the Johnny’s Research Farm, we start thousands of flower seedlings each year. At this scale, we’ve found plastic trays work best for us.

When deciding on which tray cell size to use, consider the size of the seed and how long the crop is expected to be in trays. We use different cell sizes for different crops and situations; here’s a rundown of what works for us:

20-row flats (a.k.a. strip trays)

These are a helpful option early in the season if heated growing space is limited. You can start different varieties in each strip, allowing you to start a lot of varieties in a small space. These are also good if the germination rate is unknown or suspected to be low. Strip trays are best for small-seeded crops and crops that can tolerate some root disturbance, as the seedlings will have to get bumped up to a larger cell size before they will be ready to transplant out.

Note that these are shallow trays that can dry out quickly; as such they are not appropriate for crops with large seeds or taproots. It is imperative that you bump up seedlings before they become rootbound.

128 cell plug flats

This is a standard plug flat that is useful for many flower crops with small to medium sized seed. 128’s are a good balance between efficient use of soil and space while also providing a cell size that allows for a full-size seedling to develop without the need for bumping up.

72-cell and 50-cell trays

We use these larger cells for medium to large-seeded crops and for fast-growing crops that outgrow 128 cell trays too quickly. Since the cell sizes are larger, these trays allow a little longer for seedling growth and some flexibility around transplant time.

Deep 50 cell trays

The Deep 50 cell trays have extra-deep cells for crops with long tap roots and/or a long development time. This cell size helps keep seedlings from becoming rootbound, however, the larger cell size can make it a bit more time consuming to transplant seedlings.

Seeds Per Cell (Seeding Density)

We typically seed 1-2 seeds per cell. Seeding more densely than that can result in poor airflow and increased risk of disease. We thin to 1 plant per cell following germination.

Growing Resources by Crop

Lisianthus

Snapdragon

Celosia

Eucalyptus

Delphinium

Echinops

Echinacea

Sweet Pea

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Pinching Seedlings in the Tray

Pinching is the process of removing the central growing tip to promote growth of sideshoots. For some flower crops, pinching is helpful in increasing plant productivity. Pinching is not recommended for all flower crops; check the growing instructions for guidance on whether or not to pinch.

For crops where pinching is beneficial, we sometimes pinch seedlings while they are still in trays. Typically, we do this if we know we aren’t going to be able to transplant in a timely manner and we know we are going to pinch them eventually anyway; in this situation we may pinch in the trays to slow down the plant growth and to ensure we don’t miss the appropriate window for pinching. Snapdragon, zinnia, cosmos and celosia are all crops where we have sometimes chosen to pinch in the tray. While inching in the trays is not standard practice for us, it is a helpful option sometimes.

Common Seed Starting Problems

Review our Guidelines on Seed Starting Indoors for advice on avoiding common problems such as damping off (sudden death of seedlings); stretching and legginess; and rootbound plants.

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