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Please note that any order placed after the 15/04/2024 will ship after the 26/04/2024.
What is Seed Starting? why and when start your own seeds indoor? sowdiverse.ie

What is Seed Starting? Why and when to start your own seeds indoors?

Why and when to start your own seeds indoors

If you ever wondered what to grow, how to and when to start your own seeds, we hope this guide will help you.


Why start your own seeds?

  1. The obvious reason is that you will get to enjoy the fruits of your labor earlier. Earlier harvests jump start your season!
  2. You control exactly how the seeds have been grown. You know exactly when you planted the seeds, how long they have been around before being planted, where they came from. When you buy seedlings from a nursery, where you don't know how long they've been sitting around before you purchase them. You also control the quality of what you're planting. Any weak or stunted plants can be disposed of as opposed to being planted and failing. In summary you do your own quality control.
  3. You get more for your money. Even after the costs of the seed starting supplies (seeds, compost, pots), growing your own plants to transplant in the ground when the temperature is warmer is still more cost effective and you get to choose what you grow! A packet of seeds only costs a fraction of what a tray of seedlings grown by a nursery would cost.
  4. You get to choose the varieties you grow. Nurseries seedlings tend to only be "tried-and-true" varieties. They grow what sells the most to the bigger public. If you start your own seeds, the possibilities are endless. A nursery may only stock 4 varieties of tomato seedlings, one variety of aubergine, no tarragon herb while ordering and planting your own seeds may give you the choice of over 50 varieties. Variety is the spice of life! And you will be helping biodiversity.


Seed Starting At-a-Glance

Vegetables and herbs germinate best in warm soil. Soil temperature plays a critical role in the success of your seeds, whether you are starting your seeds indoor or outdoor. We have listed below a few common vegetables with the temperature needed and when to plant them. You may be surprised at how easy it is for the seeds to germinate.



Sow aubergine seeds indoors 8 to 12 weeks before last frost. Sow seed at 1/2 cm at soil temperature of 23C and lightly cover. Seeds sprout in 10-15 days. Plant in polytunnel or transplant out when they are at least two sets of leaves after danger of frost. It is advised to stake the plant. Space plants by 60-80 cm.


Cape gooseberries or ground cherries

Sow cape gooseberries seeds indoors 6 to 8 weeks before your last frost. Place your seeds on top of the soil and then cover lightly with a thin layer of soil, about 1/2 cm. Pat soil gently. Keep soil moist. Seeds sprout in 7-10 days. When the plants are established, thin them and give them about 70 cm to spread. If you choose to direct sow, plant seeds out after your last frost.



Sow cauliflower seeds one seed per module indoor in February/March at 18C soil temperature. Lightly cover with soil. Seeds sprout in 8-15 days. Sow outdoors from Mid-May for summer crops when soil temperature reached 18C. Space plants by 50 cm.



Sow courgette seeds indoor 4-6 weeks before last frost at 18C soil temperature. Seeds sprout in 5-14 days. Transplant in the polytunnel when all risk of frost has passed, leaving 1m between the plants.



Sow cucumber seeds indoors 6 weeks before last frost if you will be growing them in a heated greenhouse. Sow cucumber seeds on their side, 1–2 cm deep, in small pots. Keep them at 21C. Or Sow directly outside after the last chance of frost has passed and the soil temperature is at 21C. It is recommended to give the plant support.



Sow lettuce seeds indoors from late April. Sow 3 or 4 seeds in a pot over the top of regular compost, water gently, lightly cover with. Seeds sprout in 7-15 days. Keep soil temperature above 16C. Place in a warm, bright spot, such as a sunny windowsill, and water regularly to keep the compost moist. When the seedlings are large enough to handle and have their first true leaves, transplant into their final growing space. Distance plants by 30 cm apart.



Start indoors 3-4 weeks before last frost. Sow 1.5 cm deep at 21C soil temperature. Direct sow in a polytunnel after last frost when soil temperature is over 21C.



Sow okra seeds indoors 4-5 weeks before last frost. Sow 1/2" deep. Keep soil temperature above 24C. Transplant in polytunnel when first true sets of leaves have appeared. Space plants 12-18" apart.



Sow pepper seeds 8-10 weeks before last spring frost. Seeds sprout in 20-30 days at 24C soil temperature. The warmer the temperature, the faster they will grow. After danger of frost, transplant to greenhouse with 16-24 inches between plants.  Suitable for succession planting for a continuous harvest. It is advised to grow this pepper in a greenhouse or sunny sheltered spot since they need high temperature to grow.



Sow squash seeds indoors 3-4 weeks before last frost. Sow 1.5cm deep, 1-2 seeds per pot. Provide 21C soil temperature. Germ 7-15 days. Transplant out 36" apart without disturbing roots. Sow indoors from late March through April if growing in the greenhouse, or late April through May to transplant outdoors. Thin to keep the strongest seedling. When large enough to handle, transplant seedlings into bigger pots. Leave 60-80 cm between the plants.



Sow tomato seeds indoors 6-8 weeks before last frost. Sow seed in a propagator from March and keep soil temperature at 24C. Seeds sprout in 7 -14 days. Keep small plants in a sunny, frost-free environment until they can be planted in the greenhouse from late April or outdoors in late May. Space plants by 61-91cm.


The last spring frost will vary on your location. You can check the last spring frost day in your area here.


What do you need for a successful seed starting?

1-The first things you need to get are obviously Seeds. You decide what you want to grow and where you buy them from. There is no point buying organic seeds if you are not going to grow then in an organic garden or compost. It makes sense though to buy Heirloom, open-pollinated, untreated or chemical-free seeds to plant for your household. At Sow Diverse, all our seeds are open-pollinated, untreated, chemical-free and we have a good selection of Heirloom seeds.

2-A soilless mix/seedling mix. Soilless mix is a sterilized mixture of core fibre, vermiculite, perlite, and other material depending on the brand. Being sterilized, the soilless mix helps prevent any diseases that might have been in any soil you would use. Most of the time, potting soil can be too heavy for germination. It is coarser and could include weed seeds or soil that hasn't been sterilized. You certainly do not want any disease or unknown/unwanted weeds in your own seedlings. Potting soil can also get water logged (overwatered) and can lead to seed rot or disease, such as damping off. Seedling mixes are usually very fine, allowing the tender new roots to spread out and offer good water drainage. Unfortunately, though, Seed starting mixes usually do not have to enough nutrients to keep your seedling growing strong, so a fertilizer may need to be added (see below). 

3-A seedling mat or a propagator (optional): A good way to give your seeds the warm soil temperature they need to germinate is by using a propagator or a seedling Heat Mat. They help the soil warm up and therefore help create the ideal growing environment that your seeds demand.

4-Another essential for the seed starting process is a set of grow lights, a south facing sunny windowsill or a warm conservatory. Grow lights simulate sunlight where there is none. A sunny windowsill or a conservatory depends on your house layout. It is essential to place the seedlings in a location where they get the amount of light they need to grow.

5-The optimum time to start lightly fertilizing your seedlings is after the second to third set of leaves appear on the seedling, as the seed starting mixtures may not provide adequate nutrients. You can use an organic fertilizer such as liquid seaweed. Some seeds do not require fertilizing but some are heavy feeders such as tomatoes and aubergines.

Click HERE to buy seeds at Sow Diverse.