Guide to growing tomatoes like a master gardener

Tomatoes are relatively easy to grow, but to be successful, you must provide the proper support and care throughout the plant’s life cycle.

To make it easier for you to become a master at growing tomatoes, read the following guide to learn how to start, transplant, and care for your tomatoes like a professional.

Part 1: Starting tomato plants from seed
Part 2: Transplanting tomato plants outdoors
Part 3: Caring for your tomato plants

To be successful, follow the advice below, and you will be rewarded with a plentiful harvest.

If you buy tomato plants at your local nursery, just skip ahead to Part 2 - Transplanting tomato plants outdoors.

Part 1: Starting tomato plants from seed

Home gardeners of all levels can start tomato plants from seed. It is not difficult but requires space, time, and presence. 

Do not start your seeds if you plan to spend a weekend away. Your starter pots will need daily check-ups, even if it is a relatively hands-off process.

Part 1 looks at home gardeners’ most common mistakes when starting tomato seeds indoors.

1. Choosing to grow the wrong variety of tomatoes

Picking a tomato variety includes deciding between determinate and indeterminate varieties. And when you have decided there are modern hybrid varieties, heirlooms tomatoes, cherry tomatoes, plum tomatoes, beefsteak tomatoes, and we are yet to discuss size, shape, and color. 

Short glossary, determinate plants are bushier and smaller in size. Indeterminate tomato plants grow large and will require staking and support.

My best advice, look at your available spaces and then ask yourself when and what you want to harvest.

• Early and plentiful harvest? Choose an early hybrid variety.
• Lots of space? Indeterminate could be an option for you.
• Small space? Choose a smaller-sized determinate tomato variety.
• Bountiful harvest? Go with hybrid varieties, as heirloom varieties often yield less.
• Do you want to pick snack-sized tomatoes as you walk through your garden? Go for hybrid cherry tomatoes for an early and plentiful harvest.
• Beginner at growing tomatoes? Choose a determinate, disease-resistant hybrid variety.

There is no one-size-fits-all when it comes to tomatoes. But if you want to make it easy on yourself, choose a determinate, hybrid variety for more, and often larger and fuller, fruits per plant.

2. Avoid the all-or-nothing approach to seed starting

Starting any plant from seed is a living process. And sometimes things go wrong. There can be unexpected shifts in temperature, unforeseen drafts from open windows, heavy-handed watering, or simply forgetting to water our starter pots.

In short, several things can go wrong. The solution is to start batches of seeds a week or so apart.

Suppose you are planning to grow 10 tomato plants in your garden. Start 10 plants by placing 2-3 seeds in each of the 10 starter pots in week 1. Wait 7-10 days, observe your first set of pots, and if needed, start another batch. 

If you end up with too many seedlings, no problem. Thin out the seedlings and keep the strongest. And trust me, if you have too many healthy seedlings, you will have no problem giving them away to friends. 

3. Starting seeds too early

Each tiny seed you plant can grow into a full-sized plant. And tomato seedlings do grow fast when they start to develop. 

If you start too early in the year, you will end up with tomato seedlings needing sunlight that you must provide. 

Unless you have full spectrum growl lights and plenty of space, start your seeds 6-8 weeks before the last expected frost date. 

Tomato plants like warm soil, and it makes more sense to wait a week longer than to be too early.

Yes, I am guilty of making this mistake over and over. I plant too early and end up with tomato seedlings on every conceivable indoor surface. I remember the following year, and then somehow, itching to get going, I make the same mistake again the next year.

4. Not looking after the seedlings

You want solid and compact seedlings—and tomato seedlings like warm soil, even soil moisture, and plenty of light.

And if your tomato plant needs 6-8 hours of natural sunlight, you need to use grow lights for 12-16 hours per day. Or you could wait and use the tried and tested window sill method when there is more sunlight. 

Weak, leggy seedlings are not where you want to start. Sure, you can repot your seedlings deeper, and roots will grow from the stem, but look after your seedlings for the best results.

5. Forgetting to report the seedlings

Tomato seedlings grow fast and need space to develop. Your tomato seedlings are ready to be transplanted into a larger pot when they show a minimum of four true leaves or two pairs of true leaves. 

Failing to pot up tomato seedlings will result in stunted growth, yellow leaves, and even dead plants. 

And yes, depending on the variety you have chosen to grow, you may need to repot your tomato plants more than once.

Please read our article on How to transplant tomato seedlings for more details. 

Part 2: Transplanting tomato plants outdoors

As spring approaches, your tomato plants are getting big, and you cannot wait to move them out into your garden.

But a few common mistakes can undo all your efforts up until now. Here are the top 8 mistakes I see home gardeners make when moving tomato plants outdoors.

1. Forgetting to harden off seedlings

Your seedlings have lived a sheltered life indoors and are now used to your indoor climate.

Before permanently moving your plants outdoors, you need to introduce them to their new growing environment gradually. This process is referred to as hardening off your plants or seedling. 

Start by placing your pots outdoors for an hour, and avoid direct sunlight. Increase time spent outdoors over the next 7-10 days before permanently moving your plants outdoors. I introduce direct sunlight about halfway through the process.

If you do not harden off your seedling, you may experience what is commonly referred to as transplant shock. Your plants will react adversely, and you may see brown or white leaves on your tomato plants. 

Be patient and spend some time hardening off your plants. It is worth it.

2. Transplanting tomato plants too early

Tomatoes need warm soil to grow correctly. Move your plants outdoors once the minimum temperature is consistently above 10 degrees Celsius (50 degrees Fahrenheit). And yes, nighttime temperatures are included. 

Transplanting too early can result in frost damage, poor growth, and small fruit production. 

Again, be patient.

3. Location – planting in the shade, windy or otherwise poor areas

Tomato plants want a minimum of 6-8 hours of direct sunlight to grow and thrive. 

Look closely at the location you selected. Will your plants get enough sunlight? Are the plants evenly exposed to sunlight, or are some plants blocking others? Is it windy, far away from a water source, or too hot?

Ideally, choose a location with plenty of sunlight but at least partial shade during the hottest time of day. A bit of wind is suitable for airflow, and check to ensure you have a water source nearby. Your tomatoes will require frequent watering in summer.

4. Not rotating your tomato plants

Plant your tomatoes in a different place than last year. It is as simple as that.

Tomato plants are vigorous growers and consume a lot of goodness, resources, and nutrients from the soil. Planting in the same spot every year can lead to soil-borne diseases and nutrient depletion.

Give your plants the best possible start by improving the soil before planting or choosing a different location than last year. 

5. Forgetting to repot tomato plants deeper

Tomato plants will grow new roots from the stem if transplanted deeper than they were growing.

This is excellent news if your seedlings are a bit leggy. But even if you have solid and compact seedlings, plant them deeper to help develop a robust root system

6. Provide support before your plants need it

Tomato plants grow tall, and even the bushy determinate varieties get top-heavy when they start to fruit.

Use tomato cages or stake you plant before they need it. Ideally, get your support structure in place as you transplant your tomatoes. 

Inserting support later is more complicated, and you risk causing damage to the root system.

7. Crowding the tomato plants

Tomato plants need room to grow and develop. Planting tomato plants too close together leads to poor air circulation, competition for resources, and uneven distribution of sunlight.

Poor air circulation unnecessarily introduces the risk of plant diseases, whereas uneven light and competition for resources will give you a smaller harvest. 

8. Not watering enough when transplanting outdoors

No plants like the root system to sit in constant wet. It can lead to root rot and all kinds of nasty diseases that will stunt growth and even kill your plant.

But there is one exception to this rule.

You should water a lot when you move your plants to their final location, whether in the ground, a raised garden bed, or a container.

And I mean a lot, as in water collecting on top of the soil. The roots need a proper soak to get going in their new home.

This is also a good test of how well-draining your soil is. The water sitting on top in puddles should not take minutes to be absorbed and disappear. 

Part 3: Caring for your tomato plants

Established tomato plants are not demanding. Still, for a bountiful harvest, a few essential tips and tricks will ensure your success. 

1. Do not overwater

Tomato plants are thirsty and require even soil moisture and regular watering. You will need to water daily, at least during the hotter times of the year. 

But you do not want to overwater. If the root system constantly sits in wet soil, you risk root rot and other soil-borne diseases.

Do not get the leaves wet when you water, and avoid watering your plants several times daily. Instead, give your tomato plants plenty of water in the morning and check on them during the day. Use your finger to get a feel for the level of soil moisture. 

You may need to water morning and late afternoon during the hotter periods of the year but avoid watering when the plant is exposed to direct sunlight. I typically water in the morning during spring and early summer, but both in the morning and evening during the hottest times of summer.

2. Do not let your tomato plants dry out

Conversely, insufficient water for your tomato plants will lead to stunted growth and poor fruit production.

I must mention this as tomato plants will require daily watering for much of their life cycle. 

If you remember to water your plants daily, you should be ok. The problem with underwatering typically happens when you forget to water your plants altogether, especially if they grow in containers or grow bags where the soil will dry out quicker. 

3. Not providing enough sunlight

Tomato plants need a minimum of 6-8 hours of sunlight per day to grow properly. We cannot control the weather, but we can choose an optional spot in our garden.

Ensure your tomato plants have enough light, even as everything else in your garden starts to develop and grow tall.

4. Fertilize your tomato plants

Tomatoes are vigorous growers; you need to fertilize your plants if you want a bountiful harvest.

Here the rule is to feed your tomatoes fertilizer weekly instead of daily smaller doses. Using a well-balanced fertilizer with an NPK of 10-10-10 is a good start.

Related: To achieve even better results, read the article "Guide to fertilizing tomato plants for ambitious home gardeners" for easy-to-follow guidance and instructions

Mix a small dose of water-soluble fertilizer into our watering can and feed your plants once a week.

You can also feed your tomatoes by adding compost or placing fresh grass clipping around your plants throughout the growing season.

5. Pruning incorrectly

There are lots of advice and theories about when to prune tomato plants for maximum yield.

Generally speaking, I live by two straightforward rules, which work great for me. 

• Determinate: Do not prune determinant tomato varieties. 
• Indeterminate: Prune suckers and side stems that are unlikely to produce fruit late in the season.

But as always, there are exceptions to the rule.

I don’t actively seek out and prune suckers on determinate tomato plants. The plants are bushy and compact, and I have never had to prune stems or suckers to get a good harvest. But I will prune lower leaves and side stems that go yellow or where there is a risk for leaf-to-soil contact. I also prune determinate plants if they grow too dense; proper air circulation is vital, and I want to see the main stem.

I do, however, prune indeterminate tomato varieties. I actively seek out and prune suckers as I spot them. And later in the season, I will prune side stems that are late to develop to allow existing fruit to mature and ripen. This also improves airflow and overall plant health.

Use your fingers to prune smaller-sized suckers. For tougher side stems and suckers, use clean, sharp garden scissors or cutters. Do not attempt to pinch larger stems or branches with your fingers. A sharp cutting tool will deliver a cleaner cut.

And if you are unsure, do not prune. Cutting too much or at the wrong time can cause more damage than it is worth. 

Related: Read the Guide to pruning tomato plants for home gardeners for detailed information on the how, when and why to prune indeterminate and determinate tomato plants. 

6. Forgetting to check for pests

Like most plants, tomatoes are susceptible to various pests, including aphids, leaf miners, and powdery mildew, to mention a few we have faced over the years. 

And here, regular inspection and early detection are critical. Inspect your plants daily to catch problems early. 

Early detection will allow you to manually remove pests like stink bugs or cut infected leaves or branches. Another option is to use an organic treatment like Neem Oil to fight the infestation. 

7. Mulch is your best friend

Tomato plants are thirsty and want even soil moisture. Mulching your bed can help you regulate soil temperature and retain moisture during hot summer days. 

Mulching the garden bed will also prevent the growth of weeds competing for resources and nutrients and create a barrier between the plant and potential soil-borne pests and diseases. 

Mulching is easy. Add about a 5 cm / 2 inches thick layer of straw, shredded leaves, or pine needles to help insulate and protect your tomato plants as they grow.

Summary and conclusion

This is a long and comprehensive article. But truth be told, many things need to be done right once. So do not get overwhelmed.

And as for tasks like watering and inspecting your plants, you were going to do it anyway; this guide helps you do it correctly.

Here’s to your success. Please send us photos as you evolve into a master tomato grower.