Notes by Kat Lavers, September 2022
Why grow from seed?
With practice you’ll be able to grow stronger, healthier seedlings than you can buy from a nursery, which leads to better yields from your home vegie patch. The cost of a packet 50 seeds is often the same as a punnet of 8 seedlings, so you’ll save money and also cut the plastic waste and transport fuel associated with commercial seedlings. By saving seed from your best plants, over time you’ll breed plants that are perfectly suited to your tastes and conditions, as well as increase your resilience.
Which plants are grown from seed?
Most annual vegetables and plants are grown from seed. Common exceptions are potatoes (although confusingly the small pieces of potato used to plant these are still referred to as ‘seed’) and garlic. Many perennials are propagated using other methods like division, cuttings or grafting.
Sowing in punnets
A punnet is a small container designed to raise seeds before they are planted into their final growing position. Sowing in punnets makes it easier to keep seeds moist and protected from pests. Small containers tend to warm up earlier than the ground in spring, and they allow the current crop to grow for longer in beds while the next crop of seedlings is getting started in punnets. Standard nursery punnets are only 5cm tall, but I prefer to use deep 8.5cm punnets for most larger vegetables to allow better root development before planting out. These can be sourced for free from nurseries with pot recycling programs.
What seed raising mix should I use?
Punnets are filled with seed raising mix that provides a moist but aerated environment for the seeds. Commercial seed raising mix has a light, sandy structure that provides ideal aeration and texture for seeds to germinate and is pasteurised for disease control, but it also contains few nutrients and dries out quickly, so seedlings either need to be transplanted quickly or provided with a liquid fertiliser. In hot weather the punnets may need watering many times each day which isn’t practical for most home gardeners. It’s also an extra cost, and comes wrapped in plastic and transported long distances. For these reasons I prefer to make my own seed raising mix using this recipe:
3 parts sandy soil (or potting/seed raising mix) : 1 part compost or worm castings
Compost or worm castings improve moisture-holding capacity and add nutrients, and make it easier for home gardeners to achieve good results.
If your soil is very clayey, add sand to improve the drainage of the mix and use less compost or worm castings. Experiment with a few ratios to find the best recipe for your soil type.
Keep in mind that your own soil and compost/worm castings will have weed seeds that will also germinate. This can be confusing for beginners but with a little practice and by sowing in a planting pattern it is obvious which are the weeds and you can pinch them out. Pests like earwigs, slugs and snails might also find their way into the mix, so check your punnets regularly (especially at night) for the first few days. There is a risk of introducing diseases. If you prefer you could substitute commercial potting or seed raising mix for garden soil, and use a commercial worm casting product that has been pasteurised to destroy seeds and pathogens.
How do I sow seeds?
1. Fill punnet with seed raising mix level with edge
2. Press down gently and evenly
3. Poke holes no deeper than twice width of seed. For small
vegetables in shallow punnets (shown opposite), use 6-8 holes.
For larger plants make only 3-4 holes and use a deeper punnet
4. Sow 2-3 small seeds or 1 large seed in each hole
5. Pinch over or sprinkle over more mix to cover, and label
6. Water the seeds in gently
If the seed is old or small, sow extra in each hole to compensate for poor germination. As the seeds grow you may need to thin them out so there is one plant per hole (or per punnet for larger plants) otherwise seedlings will be stunted by the competition. Pinch out the weakest seedlings so the remaining plant/s can grow strong. A punnet of 6-8 plants works well for small plants like salad greens, or for large plants like zucchinis and tomatoes you can thin to only 1 in each large punnet.
Where should I put my punnets?
Most seeds don’t require light to germinate so if the weather is cold they can be kept indoors for extra
warmth until they sprout. After germination they require bright light for strong growth, so move them outdoors. Keep your seedlings in a place you will notice them regularly so you remember to water and watch for pests.
When are my seedlings ready to plant?
When the seedling reaches the height of the punnet it is ready to be planted into the bed, but they can wait a bit longer (until older leaves begin to yellow) if necessary. As a rough guide, seeds raised in punnets will usually be ready to plant out in about 6 weeks.
Sowing directly in final position
Sowing seeds directly in beds or pots avoids any root damage or transplant shock. Carrots,
coriander, dill, beans and peas are best planted this way. Seeds sown direct are more vulnerable
to pests, so manage these before planting out.
Prepare your bed or pot by raking it until the surface is smooth and level with an even crumbly
structure. Small seeds may run out of energy before they reach the surface if planted too deeply,
so plant seeds at a depth no greater than twice their width. Plant extra to allow for casualties
and thin them out later to the right spacing.
Seeds must be kept consistently moist while germinating or they may die. Expect to water once daily in cool weather or twice daily in hot weather. On very hot days (>35C), move
seedlings in punnets into the shade and/or put them in a tray with 1cm water to keep them
moist. Use an old bed sheet or shade cloth to protect seeds sown directly.
A homemade bottle top waterer is a handy tool to avoid blasting little seeds out of the soil or punnet. Water until a few drips come out of the bottom of punnets, or until at least the top 10cm of the bed is evenly moist like a damp sponge.
|Was the seed fresh and stored in cool, dark and dry conditions? Were seeds kept moist while germinating? Was the soil temperature and time of year correct for germinating this seed? Check the seed packet for any special requirements and expiry date.
|Seedlings are damaged
|Check area around punnets during the day and at night when many pests are most active. Remove by hand if possible, or move seed raising to area with fewer pests. Are the seedlings healthy? Weak seedlings are more attractive to pests like aphids. Try boosting them with a weak seaweed extract or worm tea.
|Seedlings have long stems and are leaning over
|Vegetable seedings will lean towards the sun and stretch out their stems if they aren’t in a bright position. Move to a brighter spot immediately as it’s hard for seedlings to recover if they become too weak.
|Stems become thin and rot at the base, seedlings fall over
|This is a fungal disease known as ‘damping off’. Were the seedlings over watered, or kept in an area with insufficient sun, high humidity and poor air circulation? Was the soil temperature too cool?
|Oldest leaves on
seedlings are turning
|Indicates that seedlings are running out of nutrients. If seedlings in punnets are big enough, plant them out now so they can access nutrients in the bed or pot, or if the final planting position is not ready you can water with a weak organic liquid fertiliser. Use more compost or worm castings in the seed raising mix next time.
Notes by Kat Lavers, www.katlavers.com IG: @kat.lavers