Homegrown tomatoes from seed to bountiful harvest
Tips on growing tomatoes from seed. Covers where to get heirloom seeds, how to sow them, benefits of growing from seed, watering and temperatures, and the best compost to use. Includes two instructional videos.
This is the first part of the Growing Tomatoes from Seed Series. It continues on with pricking the seedlings out, planting tomatoes in the greenhouse, growing them on, harvesting the fruit, saving seed, and preserving tomatoes.
One of the most delicious and worthwhile crops to grow is the humble tomato. The scent of its sun-warmed leaves is synonymous with summer and that’s aside from the real prize – the fruit. You’ll see them start as little yellow flowers. After being pollinated they develop a tiny green bud that swells ever larger from hard and green to plump glossy orbs. Small cherry types, medium sized romas, and gigantic sculptural heirlooms. Their beautiful shapes and colours are only surpassed by their delicious sweetness. No supermarket tomato can compete in flavour.
Contrary to what it might seem, it’s not difficult to grow tomatoes, even from seed. This is the first in a series of pieces I’m sharing this year to help you get started. We’ll begin with growing tomatoes from seed. Later pieces will cover pricking out, planting out, tomato plant nutrition, staking, harvesting, and preserving tomatoes.
Grow from plants or from seed
Most people grow their tomatoes from small plants that they purchase in spring. They’re common enough to find both at your local garden centre or even online. It’s perfectly fine to start this way and can save a lot of time if you’re running late.
I’ve had plants off a friend who grows tomatoes commercially and have also been sent tiny plug plants from a seed company. I also start tomato plants from cuttings and overwinter them and grow tomatoes from seed. Each method has its time and place but there are some real benefits to starting with seed.
Seeds cost less than plants, are fun to grow since they can be sown so early in the year, and there’s an astonishing variety to grow.
Benefits of growing tomatoes from seed
There are currently over 10,000 tomato cultivars in the world. How many of those do you come across as plants for sale? Growing from seed means that you have so much more choice in the types of tomato you want to grow. From tiny berry-like currant tomatoes to beefsteak types that weigh up to three pounds at harvest like Gigantomo.
This year I’m growing five varieties, all in my standard sized greenhouse. They include Ailsa Craig, Black Russian, Sungold, Red Pear, and Costoluto Fiorentino.
Some of the best places to find rare and unusual tomato seeds are heirloom seed catalogues. Here are some places you can browse online.
Growing tomatoes true to type
Some people will point out that tomatoes grow easily from volunteers in the compost pile, or from seeds from supermarket tomatoes. However, it’s much better to start your plants from seeds or cuttings.
The most important reason is so you can grow your plants true to type. Tomatoes will happily cross-pollinate with one another so seed from unknown growing conditions could leave you with plants that produce a very different type of fruit. For example, growing seeds from a big beefy tomato can result in plants that produce much smaller tomatoes with different flavour, texture, and colour. It’s a gamble.
Controlling Growth Cycle
Growing tomatoes from seed also enables you to control the plant’s growth cycle. Meaning you can choose when to sow, how to grow, and when to harvest.
Here on the Isle of Man we have a unique climate. The average minimum winter temperature is only ten degrees Celsius different from the average maximum summer temperature. Basically, it rarely freezes here or gets hot. Leafy greens love it but heat loving plants like tomatoes struggle.
To grow tomatoes in most places in Britain you need to start seed early, nurture the plants, and plant them in a greenhouse or poly tunnel when danger of frost is past. It’s difficult to grow outdoor tomatoes here thanks to cooler temperatures and Blight, a fungal disease.
This means that tomato plants that grow from volunteers rarely have enough time to produce fruit here. Deliberately starting off tomato plants in difficult environments can mean the difference between a harvest or not.
When’s the best time to sow tomato seeds
The time you sow your tomato seeds is not necessarily what the back of the seed packet says. Everyone who orders those seeds, from Alaska to Texas, will have the same information given to them. There are actually two factors that dictate the earliest time you should sow your seeds. Planting location and last frost dates.
It’s difficult to grow tomatoes outdoors in Britain for two reasons – temperature and Blight. Tomatoes need shelter from wind and cold and lots of warm sunshine. Blight is an air-borne fungus that affects tomatoes and potatoes and decimates most outdoor toms. That’s why most of us choose to grow our tomato crops under cover in poly tunnels, greenhouses, or in a warm conservatory in the house.
Those of you in warmer climes without Blight will be lucky enough to grow tomatoes outside. If you’re unsure about where you should grow tomatoes, ask a neighbour, garden centre, or local gardening group. They’ll know the best way for your region.
Start tomatoes under cover in late winter
Once you know the location, you can make a decision on when to sow tomato seeds. The general advice is to sow 6-8 weeks before your last frost date. However, there are actually two last frost dates to consider and they will directly relate to where you plan to plant your tomatoes.
If you’re planting under cover, your plants will have more protection. If you plant outdoors too early then you can lose all your precious plants.
Average and Safe Last Frost Dates
Most last frost dates that you find online are actually average last frost dates. That means that in an average year you won’t see any more frost after that date. This isn’t always the case though.
For example, my own last frost date is the 31st of March. However, one year we had six feet of snow in April. That’s why I consider the 1st of May to be a safe date to use as a last frost date for outdoor planting. I have more information on earliest dates to sow seeds over here.
If you’re starting tomato seeds indoors, as most of us do so early in the year, you should not use garden compost or soil. It’s because both contain weed seeds, fungi, and pathogens that can kill off your seedlings. It’s a different case for direct sowing seeds in the ground when it starts warming up. Those factors are more controlled in their natural environment.
Although many people will use standard multi-purpose compost, it’s better to use a free draining seedling compost to start off tomatoes, aubergines (eggplant), peppers, and other more fussy plants. In their early days, they’ll have nutrients stored in the seed itself to get started.
Remember growing bean seeds in damp paper towels in school? Growing tomatoes from seed begins using the same principle. It’s better to give seedlings good drainage and a fluffy material to spread roots into than dense compost they won’t make full use of.
Make your own Seedling Compost
Seedling compost is fairly standard and you can find it at most garden centres. They come in lots of different mixes that use loam, perlite, vermiculite, coco coir, and lots of other materials. The main objective of seedling compost is a fine, yet light mixture with only a dash of nutrients. A common one you’ll find is John Innes Seedling Compost, and you could make that yourself with this recipe:
• 2 parts sterilized Loam
• 1 part Peat
• 1 part coarse Sand
• For every 2 gallon (6 litre) bucket, add 10g (1/3oz) superphosphate
5g (1 teaspoon) ground chalk
If you don’t want to use peat, you can make other mixes and there are loads of recipes you can find online. For me, I think the easiest mix is just 1-part perlite to 1-part good quality multi-purpose compost. It has enough nutrients to keep plants going for a while if necessary and the perlite gives it good drainage and space for the roots to develop.
You can sow your seeds in trays or in individual pots. Trays can take more seedlings so if you’re planning on growing rows of tomatoes than that’s your starting point.
Prepare your compost by moistening it with a little tap water. Just enough to make it damp.
Fill a tray with about an inch or more of seedling compost, firm down with your hand, scatter on seeds lightly, and then cover them very lightly with more compost. You’ll see seedlings emerge in 5-14 days and grown this way, they’ll need pricking out after a 3-4 weeks.
Sowing tomato seeds in pots
If you’re just growing a few plants in the greenhouse, it will save you time if you use 3” pots. The plants will live for a longer time in those pots so the compost they’re in will need more nutrients.
In that case use my mix of 50/50 compost. Or at least 1-part perlite to two parts compost if you want to make sure they won’t need a feed before planting. Some gardeners will just use multi-purpose using this method but it really pays to give your seedlings extra drainage.
Fill the pots to about a centimetre / half inch from the top, firm down, and space out 2-3 seeds on top. Cover lightly with compost. Allow to grow and pinch out the weaker of the seedlings after about a month.
Light & temperature
To germinate, tomato seeds need a temperature of around 64-69°F (18-21°C). A little lower or a bit higher is fine but below 50°F (10°C) and above 90°F (32°C) and they won’t do well.
Because many of us start tomato seeds between January and March, it can be difficult to give those kinds of consistent temperatures. If your home or growing space is cold, use a heated propagator like you’ll see me use in the video further above.
Tomato seedlings need lots of bright light to help them grow. If you’re growing on a window sill you’ll see your plants stretching for the window. I tend to turn mine if this happens to try to even them out. In the end though, they’ll need a grow light if you’re starting them off really early in the year. Put your seedlings under light as soon as you can see growth — more details on this will be in the next piece in this series.
Tap vs Rain Water
I always use tap water to water seedlings. I pour it into a bottle or jug overnight to let it come up to room temperature and to allow any chlorine to evaporate. That way the temperature won’t shock the seedlings and the chlorine wont’ interfere with the growing process. Our tap water here is not fluoridated but if yours is, you could consider filtering it.
Some years ago I read somewhere that collected rainwater isn’t the best choice for seedlings. It’s not the water itself but the container and surfaces that water has come into contact with while it’s outdoors. Stronger and more established plants can easily deal with any microbes and fungi that it can introduce. Seedlings are a bit more sensitive.
I’m not 100% sure this is fact but I tend to stick by this. If you’ve heard something similar, or have another opinion, let me know as a comment below.
Getting the water to your seedlings without getting the leaves too wet or disturbing the compost or roots is the goal. A direct stream from a watering can or spray bottle can do a lot of damage. When watering you can choose to do a few things:
• Set trays and pots temporarily in a shallow tray of water to allow it to soak up from the bottom
• Use a rose-headed watering can
• Use a misting spray bottle
• Protect the surface of the compost with grit
This year I’m taking you with me on the full journey of growing tomatoes from seed, to plant, to harvest. Have a watch of both videos in this piece that show you how I’ve sown my own seeds and set them up to grow. Just over a week from when those videos were filmed, nearly all of the tomato seedlings are up. Now two weeks on the seedlings are growing uncovered under a grow light. Though they’re still in the propagator, I turned it off as soon as all the seeds had germinated — room temperature is fine for them.
The light I’m using is a red and blue spectrum flexible lamp that clips onto a window sill. It’s perfect for the home grower, especially if you only have a few seedlings to nurture indoors. I highly recommend it and you can find it for sale on Amazon. I’ll cover grow lights and pricking out the seedlings in the next installment in this series.When it’s available I’ll link to it just below.