Starting Seeds

Gardening Tips

For a planting guide - click here

For general gardening tips on growing vegetables - click here

Tips for Starting Seeds

Soil Temperature

This is usually the main determining factor of wether a seed will germinate or not. If you sowed the seeds correctly and they don’t germinate, incorrect soil temperature is usually the culprit. Note that this is SOIL temperature and not air temperature. This can be accurately measured using a propagating thermometer, available at gardening and hardware warehouses.
Generally, most seeds like a soil temperature of 23 degrees C. Some seeds have special requirements for lower or higher temperatures, usually depending on when they are grown in the year.

-Tomato, pumpkin, watermelon, rockmelon, zucchini, squash and cucumber germinate well within 20-26 degrees C. 

-Broccoli, cauliflower, leafy greens, carrot, lettuce, beetroot and radish like cooler temperatures of 10-20 degrees C. 

-Eggplant and capsicum can be difficult to germinate if they don’t have the right temperatures – they generally need between 25-30 degrees C. Usually much easier to germinate in warm humid climates like Sydney. 

-For herbs and flowers, generally speaking 22 degrees C is usually ideal. 

Sowing in pots indoors is the best way to monitor soil temperature, and generally improves success rates. 

For a quick reference table of the optimum soil germination temperatures click here

Soil Moisture

This may seem obvious but it is important to water the seeds enough but not too much. The soil should always be moist but not soaking wet as this will cause the seeds to rot. Ensure any pots or seedling trays are free draining or if in saucers, the water should only be very shallow. 

If sown directly in the garden, overwatering is less of an issue. Similarly, it is important not to allow the soil to dry out at any stage in the germination process. If the soil dries out at all, the germinating seed will die. For sowing directly in the garden, apply a fine layer of mulch to keep the soil moist at all times.

Watering should also be gentle to avoid washing away or disturbing the seeds. For very fine seeds like spearmint or thyme, use of a misting gun is highly recommended. 

Some seeds with thick seed coats like broad beans or winged beans may benefit from scarification or overnight soaking in warm water to soften the seed coat and improve germination rate.

Light

This is also important but much easier to control. Sow the seeds the depth recommended on the back of the packet. Generally speaking, seeds are sown as deep as twice their size.

For very fine seeds like creeping thyme or mint, surface sowing is recommended. This is because the seeds require light to germinate. Sow the seeds on the surface of fine, premium seed raising mix in a punnet. Press down gently and mist with a misting gun. Keep these indoors, near light but out of direct sunlight. Keep moist at all times with the misting gun and you should see germination within about 20 days.

Special Requirements

Some seeds have special requirements in order to germinate. Many flower and herbs seeds require 'Cold Scarification' which is a period of very cold temperatures needed to break the seeds dormancy. Seeds like echinacea and lavender for example commonly require cold scarification. 
You can do this by either sowing in winter and the seeds will sprout the following spring or by placing the seeds in the fridge or freezer.

The following method is recommended for seeds needing cold scarification:

Sprinkle seeds sparingly on the surface of pre-moistened seed raising soil and pat down so they have good contact with the soil but don’t entirely cover them as light helps with the germination. Cover pot with cling wrap, poke a few ventilation holes in and then place the whole punnet in the fridge for 4-6 weeks. The cling wrap will help it to keep moist but use a mist bottle to water if necessary. After the chill period is up, take the punnet out of the fridge during the day and place on a bench indoors but out of direct sunlight. The seeds should then germinate within 30 days at room temperature or 20-25 degrees C. Do not place the tray/pot in any direct sunlight until they germinate