How To Grow Tomatoes From Seed

Spring is the  ideal time to sow tomato seeds. They need a long growing season to make sure they mature fully and ripen. It is also getting close enough to the last frost date, so that you won’t be minding the young plants inside too long, watching them become leggy! If you are in a particularly cold area of the country, you might be best served to check your last frost date before sowing tomato seeds. More information on the last frost date is here.

So let’s get to talking about tomatoes! You may be well experienced or a complete beginner. This post is going to suit the beginner a lot more as it is a high level look at the whole process of growing tomatoes from seeds.

Why Grow Tomatoes From Seed

Let’s start with why, because you need a good reason to put the time and effort into growing your own tomatoes, considering tomatoes can be bought off the supermarket shelf so cheap nowadays. So let's look at a few reasons why.

Cost saving - Even though tomatoes can be bought for a low cost in the supermarket, it is hard to compete with the amount of tomatoes you will get from a well grown tomato plant. For a cherry tomato variety, you can be looking at getting a yield of tomatoes in the hundreds per plant! So if you use a lot of tomatoes, growing your own will definitely save you money.

Selection & Taste - One thing supermarkets don’t have is selection. Mainly you will find the same few varieties of tomatoes in all of the supermarkets. These varieties aren't always bred for their taste either, the main qualities a supermarket looks for are shelf life and appearance. The amount of tomato varieties out there is nearly endless. To limit yourself to only these supermarket varieties is to deprive yourself of trying some of the best tasting tomatoes! Our tomato seed varieties are available here.

Learning & Pleasure - The learning process of growing your own tomatoes is very rewarding, and great pleasure can be taken in picking your own fresh tomatoes off the vine for eating.

Health - You will know exactly how and where your tomatoes have been grown. It’s also unlikely you’ll ever get fresher tomatoes than the ones you pick from the vine yourself.

There are more reasons why but we’ll never get to the growing process if we keep going!

Choosing Tomato Varieties

The first step is to choose the variety or varieties you want to grow. One of the main considerations is to choose something you think you will use. At this point, deciding on how many plants to grow is wise, as you don’t want to end up with too many plants and be overwhelmed caring for them later in the year. Two of our favourite varieties are Sungold Select II and Sugar Grape. Both are heavy producing cherry types that produce really sweet tomatoes.

Supplies Needed

Some of the things you might use when sowing your tomato seeds are seedling modules, pots, compost and planting labels. A heat mat can also be useful to provide the seeds enough heat to germinate, something we’ll discuss in the next step. The only really essential components needed are seeds and compost, the rest will make life easier but are optional.

It should also be known that in Ireland, tomatoes are best grown in a greenhouse, polytunnel or under some kind of other protection. It is possible to grow them directly outdoors, but results from this are not optimal and very variable depending on the weather.

Start Your Seeds Indoors

Fill seed trays or pots with a fine compost. Plant seeds about 1 cm deep. Planting 2 seeds per cell/pot is best as this gives you the opportunity to select the best growing one in each.

Water the compost thoroughly, ensuring it's consistently moist but not waterlogged.

Once this is done, the trays or pots will need to be put in a warm location. Tomato seeds will germinate best when the room temperature is 20 degrees celsius or above. If the temperature is below this, their germination can be erratic. A heat mat can be placed under seedling trays to help bring up the temperature of the trays. Using somewhere like the hot press is also a good place to germinate tomato seeds as it is usually consistently warm.

After Germination

Once seedlings emerge, keep them inside and provide them with as much sunlight as possible. This might be in front of a south facing window, or under a grow light if you have one. Keep the soil consistently moist but not soggy.

Transplant Seedlings

When seedlings have two sets of true leaves, transplant them into larger pots if they were grown in seedling modules or very small pots.This will allow space for the roots of the plant to continue growing. Plant the stems deeply, as tomato plants create new roots from their stems.

Choose Their Final Location

This step should really be decided before starting. When choosing your tomato plant's final location, keep in mind they need heat and sun to thrive. A greenhouse or polytunnel will suit them best. You can plant them directly in the ground in a polytunnel, or if your greenhouse has a hard surface, a really large pot, planter or bucket can be used.

Harden Off Seedlings

When the risk of frost is passing, gradually expose your seedlings to outdoor conditions a week before transplanting them to their final spot. Start by exposing them to their eventual growing conditions for a few hours per day, increasing the amount of hours each day. 

Plants will take a while to get used to the new amount of sun, wind and other conditions their new climate brings. Putting them straight into these new conditions without gradually acclimatising them can set the plants back a long way, and in the worst cases even kill them.

Transplanting To Final Location

After the plants have been hardened off, it’s time to transplant them to their final location. A distance of approx 50cm is needed between each plant when you are planting them. At this point a bamboo cane can be planted alongside the plant so it is in place when the plant needs it for support as it grows.

Remove some of the lower leaves of the plant and plant deeply, so that new roots will grow from the buried stem.

Watering and Mulching

Water consistently, especially at the time of transplanting. The plants will need a lot of watering around the base after being transplanted, before their root system is big enough to find water in further away places from the plant. Mulch around the plants to retain moisture and suppress weeds.


Fertilisng will benefit tomato plants when they start to produce fruit. This can be done every couple of weeks.

Remove Suckers 

Removing suckers could be an email in itself. They are essentially new main stems that grow between the actual main stem and the leaves of the plants. If the majority of them aren’t removed, energy that could be going into producing fruit goes into producing suckers. However, letting a few suckers grow can result in more fruit per plant being produced.

Disease Control

Making sure there is plenty of fresh air flowing through your growing area will help to prevent disease. If any disease on leaves is noticed, it is best to remove these leaves from the plant as soon as possible and dispose of them to try to avoid the disease spreading..


Harvest your tomatoes when they reach full colour. Don’t leave them on the plants for too long once they ripen as this will slow down ripening of the other fruit. Enjoy the fruits of your labour!


Hopefully this might give you an idea of the tomato growing process if you weren't familiar with it already. It was just a brief look at all the steps, as each section could be expanded on greatly and be deserving of its own post! 

How To Grow Tomatoes From Seed

Subscribe To Our Newsletter

* indicates required