Whether you are a beginner or veteran, commercial or subsistence greenhouse gardener, the tomato is arguably the one vegetable you should know how to grow. In fact, it is probably the most common greenhouse vegetable and for a good reason.
For one, everyone (or at least most people) loves tomatoes. Most people also prefer fresh tomatoes to store-bought ones. Finally, tomatoes are easily one of the best vegetables to maximise the full potential of a greenhouse, especially here in the UK.
Think about it. This is a tropical crop that loves heat and warmth. Therefore, you only get a few months of “ideal tomato-growing weather” in the UK. However, you can grow for much longer in a greenhouse. You can even grow tomatoes year-round, including in the colder months. Thereby ensuring a bigger harvest and a more productive garden.
However, you must first turn your greenhouse into an environment where tomatoes can flourish. That is what we will cover in this article. So join us. Let’s discuss how to grow tomatoes in a greenhouse and get a big harvest.
The requirements for growing tomatoes in a greenhouse
There are four main requirements for creating an “ideal tomato-growing environment” inside a greenhouse. Here they are.
As stated earlier, tomato is a tropical crop. It loves sunlight and warmth, needing a minimum of 8 hours of sunlight per day.
You can meet this requirement by positioning your tomato plants where they will get enough supply of sunlight. Another option is to get professional grow lights. You will need them when natural sunlight is not enough, especially in colder months.
As a tropical plant, the tomato loves warmth. More specifically, you need to maintain a daytime temperature of about 70°-80° in your greenhouse. However, at night, a temperature of 60°-65° will be more than enough.
In a greenhouse, the primary ways to achieve this ideal temperature are:
- Thorough the heat from light sources (sunlight and grow light)
- Proper ventilation
- Keeping out the cold
- Installing a heating system.
You should get a thermometer to monitor the temperature inside your greenhouse.
Tomatoes prefer a humidity of less than 90%. Any higher, and you may have to deal with leaf mould. On the other hand, a little lower is not a problem. Shoot for a minimum of 80% during the day and 65%-75% at night.
Tomatoes prefer warm, fertile, well-drained soil with a pH of 5.5-6.8. You can meet this requirement by buying a potting mix or creating a soil mix yourself. Whatever you do, ensure the soil is healthy and free of pests and diseases.
How to grow tomatoes in a greenhouse
Ideally, the tomato-growing season starts in early spring. However, we have already established that you can start earlier or later when growing in a greenhouse. The only rule is that your greenhouse must meet the growth requirements.
However, before we talk about “how to grow”, let’s talk about “what to grow”.
What types of tomatoes can you grow in a greenhouse?
If you want the simple answer, go for varieties like black opal, Sungold, Ferline, Capprica, Craigrella and Gardener’s delight. However, you can also ask a more experienced greenhouse gardener or expert for a recommendation.
Whatever you do, we strongly recommend a disease-resilient variety. Infestations can be damaging within the enclosed space of a greenhouse.
Finally, you also need to choose between indeterminate and determinate varieties. Indeterminate tomato varieties are the most common type. They grow bigger. So they take up more space and need support structures and pruning. However, they produce fruits continuously.
On the other hand, determinate tomato species are smaller in size. So they are more compact. They also don’t usually need support structures or pruning. However, they produce all their fruits at once.
Keep all of these in mind when making your decision.
How to sow tomatoes in a greenhouse
Follow these steps to sow your tomatoes.
- Sow the seeds: Start your greenhouse tomatoes in a smaller container, seed tray or propagator and then transplant seedlings into the final container. Sow the seeds in a hole of 1-2 inches. Then wait for them to germinate. The seedlings should be ready for transplanting in two weeks. By this time, they will be about 4-6 inches tall.
- Prepare to transplant: Choose a permanent home for your tomatoes. You can use containers with drainage holes, raised beds or grow bags. Then prepare the growing medium, your soil or potting mix. If using a self-made soil mix, add compost to improve fertility. Finally, moisten and loosen up the growing medium.
- Transplant the seedlings: Uproot and transplant each seedling into a separate container. Add fertilizer, then wait for a week before watering.
How to care for greenhouse tomatoes plants
Now that your greenhouse tomatoes have started on the right foot, here are our final tips for helping them develop into healthy and fruitful adults.
Water your tomatoes regularly and cautiously
You want the soil to be moist and warm, not dry or soggy. To achieve this, water your tomatoes every day or every other day. If doing this by hand, water the soil directly and mist the plant’s leaves. If using an irrigation system, go for drip irrigation.
Make sure your tomatoes get enough air
You’ve already started well by giving each tomato plant its container. Here are three more ways to improve air circulation.
- Open the windows and vents to let in hot air during warm months
- Get an exhaust fan
- Install a dedicated ventilation system
Feed your tomato plants with fertiliser twice or once a month
Use a high-phosphorus fertiliser. More importantly, apply the fertiliser at least 2-4 inches away from the plant. This will prevent scorching.
Install support structures
This will protect the tomato plants from getting knockdown by the weight of their fruits. Use trellises, cages or stakes. Install the support while the plant is still young.
Prune excess shoots and fruits
Only indeterminate tomato varieties require pruning. Do these.
- Remove lower and side shoots to encourage fruiting and improve air circulation.
- After the plant starts fruiting, reduce each cluster to the biggest and most well-formed 4-5 fruits. The remaining fruits will be better off because of this.
Help pollinate your tomatoes
The tomato is a self-pollinating plant. However, all indoor tomatoes (including greenhouse tomatoes) need help with pollination. It’s not complicated. You just need to distribute the pollens using the following.
- Your hands
- A regular or electric brush
- Blower or
- Mist blower
- Mechanical pollinator
Watch out for pests and diseases
Common tomato pests are whiteflies, flea beetles, nematodes and aphids. Common diseases are damping, root rot and fusarium wilt. Everything discussed so far will help reduce the risks of pests and diseases. However, if they do appear, treat the problem as soon as possible.
Your options include the following.
- Removing the pests
- Setting sticky traps
- Using insecticides
- Removing infected leaves, plants and soil.
The key to growing tomatoes in a greenhouse is to get everything right from the start. That includes the tomato variety, growth requirements and maintenance.
Your tomatoes will be ready in 50-100 days. However, before harvesting, wait as long as possible to allow the fruits to ripen fully.