Growing Veggies from seed
Notes by Kat Lavers, August 2024
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 in which seeds are raised 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 texture that provides ideal aeration for seeds to germinate and is pasteurised for disease and weed control, but typically contains few nutrients, so seedlings either need to be transplanted quickly or provided with a liquid fertiliser. Commercial mixes dry out very quickly and in hot weather the punnets may need watering a few times a 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
Most home gardeners have better results with this mix because compost or worm castings improve moisture-holding capacity and add nutrients.
There are a few drawbacks to keep in mind. 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 you can recognise the weeds and pinch them out. Pests like 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 also a small risk of introducing diseases. If you prefer you could substitute commercial potting or seed raising mix, and use a commercial worm casting product that has been pasteurised.
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.
How do I sow seeds?
- Fill punnet with seed raising mix level with edge
- Press down gently and evenly
- 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 if possible
- Sow 2-3 small seeds or 1 large seed in each hole
- Pinch over or sprinkle over more mix to cover, and label
- 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. If you want to start seeds early you can bring them indoors to a warm room at night until the weather warms up. 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.
Watering
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.
Troubleshooting
| Seed doesn’t germinate or germinates poorly | 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 by pests | 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 yellow | 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. |
Other propagation methods
Division
An easy technique for plants with a clumping habit that form multiple growth points (eg. sorrel, rhubarb, lemongrass). Dig up the clump, separate the growth points ensuring there are some good roots on each, making cuts with secateurs or a sharp spade where necessary. Trim older leaves back to assist with recovery.
Runners
Runners are horizontal stems and form above the ground with baby plants forming along them (eg. strawberries). Simply dig up the baby plants carefully and cut the stem to detach from the mother plant.
Suckers
Suckers are shoots that emerge near the base of some plants (eg. currants, figs, olives, raspberries, bananas). Dig them up carefully with some roots attached.
Cuttings
Cuttings are plants grown from detached piece of the mother plant (eg. stem, leaf). Cuttings are a race between root formation and rot. Usually, hardwood cuttings are in taken in winter, softwood cuttings in spring.
Nodes are the points where leaves or roots form along the stem. Cut sections 10-20cm long with >4 nodes. Note which way is up J I cut flat on the bottom by convention. For evergreen plants, strip off most of the leaves to reduce moisture loss.
Insert into potting/seed-raising mix, keep moist and be patient.
If your first attempt is unsuccessful, you can experiment with different types of cutting and times of year. Check recommendations for taking cuttings of your chosen plant. Some do better with some new growth, some a particular length, some like a ‘heel’ at the base etc. To improve strike rate, you can try bottom heat, a plastic bag as a greenhouse, honey as a rooting aid, or just take a lot of cuttings.
Cuttings in water
Many plants will form roots in water. Water propagation is successful for many soft-stemmed plants, but also some woody, (eg. mint, tomato, sweet potato, pepino, sage, rosemary, fig, many houseplants like begonia, heart-leafed philodendron and pothos).
Layering
Layering is easier than cuttings because there is less risk of the new plant rotting or drying out before it sets roots. Use a brick or rock to pin a node on a low branch in contact with soil. Sometimes wounding to expose the green cambium layer is helpful.
Air layering
A more complex technique where a shoot in the canopy of a tree is ring barked. The cut is surrounded with potting mix and wrapped in a ball. Air layering encourages the plant to form roots even though the branch is in the air, and is useful where no low branches exist for standard layering, or where the plant is not inclined to form roots in low positions. This technique can create new plants of an advanced age.