Zinnias are a popular addition to the garden and very easy to grow from seed, germinating quickly and profusely, they are perfect for the impatient gardener.
Zinnias provide playful pops of color to your garden and can provide blooms for most of the season.
Starting zinnias from seed is the most economical way to grow a large amount of flowers for mass plantings in your garden.
Here are some tips for growing zinnias from seed.
TIMING IS EVERYTHING
In order to make the most of the gardening season, Zinnias need to be started X weeks before the last frost date. This means that in some climates, you will need to start them indoors.
Here in zone 4, we start our seeds indoors 5 weeks before the last frost date and then start the process of hardening them off after the last frost date. This ensures the maximum amount of enjoyment!
*Soil temp 23+ degrees Celsius (75 degrees Fahrenheit).
Zinnias like a warmer soil for germination so be sure to start your seeds in an area that is warmer (not a cold corner of the basement). Using grow lights helps keep the soil warm enough to germinate the seeds.
If planting the seeds outside, the soil needs to be around 23 degrees Celsius (75 degrees Fahrenheit).
Being heat lovers, Zinnias do not tolerate frost, so be sure to wait until after the last frost, and be prepared to cover them if a surprise frost comes along, especially at the end of the season. Your zinnias can last well into the fall if you protect them from frost on cold fall nights.
PLANTING ZINNIA SEEDS
To plant zinnia seeds indoors, you will need:
- Seed starting containers- tray flats or cell packs
- A good seed starting soil mix
- A container for bottom watering
- Grow light
Steps to grow zinnia seeds:
- Prepare your starting container or trays. Cell packs, soil blocks or small pots are preferred (ensure they have drainage holes).
- Fill container with soil
- Place watering tray underneath
- Moisten the soil by watering from beneath, in the tray (damp but not soaked)
- Poke holes ¼” deep (one per cell or space 1” apart in trays)
- Insert seeds (one per hole)
- Lightly cover hole with soil or vermiculite
- If you have a heat mat, you can use it, otherwise your grow light should provide adequate heat. If using a heat mat, you do not need to place under grow light until about 60% of your seeds have germinated.
- Keep soil moist and wait 3- 5 days for germination
- After germination, thin if any seedlings are weak looking
- Make sure your seedlings get 14 – 16 hours of light per day under your grow light.
- Once seedlings are larger, if they are in trays, you will need to divide them and put them up into larger pots, such as red solo cups. This is why cell packs are preferred (do not need potting up).
- Monitor the roots to ensure they do not become too root bound. Pot up if needed.
- Pinch the tops off the seedlings, just above the 3rd set of leaves for bushier plants with more blooms
- After your last frost date, harden off your seedlings by placing them outside for small amounts of time, increasing the time each day, for about 5 – 7 days. Avoid direct full sun initially and do not leave them out overnight if there is a chance of frost.
WHY YOU SHOULD PINCH OFF YOUR ZINNIAS
To encourage bushy plants with multiple side shoots that blossom, pinch off the top of the plant, just above the 3rd set of leaves. This causes the plant to grow more side shoots. Which makes even more flowers for the plant.
Pinching is completely optional. If you have lots of seeds and can plant more densely, you probably don’t need to work about pinching. But if you want to stretch your seeds, pinching is an easy way to get nice full plants with multiple blooms.
Ensure you have a good spot for your zinnias with full sun. Prepare the soil by watering and add some compost for a nice boost. Carefully transplant the seedlings without disturbing the roots, spacing as per the seed packet.
MULCHING YOUR ZINNIAS
Once your zinnias have been transplanted, you’ll notice quite a bit of empty space between your plants. You could add a little mulch in between the plants to conserve moisture and keep the weeds down. Alternatively, you can lay down other plant material, such as rhubarb leaves or tree leaves to cover the soil and add nutrients at the same time.
INTERPLANTING YOUR ZINNIA SEEDS
Depending on the look you are going for, you may consider interplanting other seeds or plants to fill in the gaps between the zinnias. In our experience, dill makes a very pretty “filler”. Other plants with contrasting colours and shapes, such as cosmos, black eyed susans, veronica speedwell or marigolds are also good candidates, depending on the height of your zinnias.
PLANTING ZINNIA SEEDS OUTSIDE
If you are planting your seeds directly outside, wait until after the last frost date and the soil is warm enough (23 degrees Celsius (75 degrees Fahrenheit).
Follow the package instructions for the recommended spacing and depth, as some varieties are larger than others. It’s important not to crowd them as they will need good circulation to prevent disease, such as powdery mildew.