COLUMNIST: ELI APPLEBY-DONALD
If you are growing in the greenhouse, you may already have planted up your tomatoes into their final home, be it a large pot or a bed in the greenhouse. If you plan to grow outdoors, June is the month to get your plants transplanted out to their bed or pots outdoors. Either way, from now on, the plants are going to grow fast and, depending on the types of plants you grow, they are going to need some care and attention.
This month, it is all about managing that growth, keeping plants healthy and productive, and staying one step ahead of Scotland’s unpredictable summer weather.
Determinate plants tend not to need as much support as indeterminates, as they tend to remain quite short. You may find you need a little support for heavy branches once the plants are fruiting, but on the whole, you shouldn't need support.
Indeterminate tomato plants though can grow tall and top-heavy fast, so they need some structure to support them. How you support them depends on where you’re growing.
You can make use of the frame of your greenhouse to tie up lengths of string, giving you something to tie in or clip the plant's main stem to as it grows.
One option I love is burying the string under the plant when you plant it, letting the roots grow around it and through the string, creating stability. Then tie the other end to the frame of the greenhouse above and either wind the plant around the string as it grows or use clips to attach it.
Wind is a real issue in Scottish gardens so stability is key. A good structure to tie your plants to, such as a trellis, arbour, or a method like the Florida Weave, will save you the heartache of toppled plants after a blustery day.
With the Florida Weave, you run strings horizontally between two strong, fixed poles. Then with each horizontal string, you weave it back and forth around each plant. With each level of string, you change direction so that the plant then has a string at the front, then the back, then the front again, and you add more lines of string as the plants grow.
One extra tip: If you’re using string, avoid natural fibres like jute or cotton as they can rot or snap as the season goes on. Go for something synthetic if you want it to last.
Although determinate and indeterminate plants are treated differently in terms of pruning, there is a bit of initial pruning I do with all my tomato plants to help keep them healthy. As your tomatoes grow fuller, it’s important to make sure there’s plenty of space between them. Airflow is important to reduce problems with disease, it allows moisture to evaporate and sunlight to reach the plants.
For this very reason, I have one non-negotiable pruning job: I always remove the lower leaves of all my tomato plants. It helps keep airflow around the base of the plant and reduces the chance of rainwater or watering splashing soil up onto those leaves. It’s a simple thing, but it makes a difference and can really help prevent the spread of disease and fungal infections.
These are the vining or cordon tomatoes, the ones that just keep growing. Think of ‘Sungold’, ‘Sweet Million’, ‘Gardener’s Delight’, and even the more fashionable types like ‘Brad’s Atomic Grape’. With these, it’s best to train them to a single stem. That means regularly nipping out any side shoots (you’ll sometimes hear these referred to as suckers) that appear where the leaf joins the main stem.
Why do we do this? Well, it helps keep the plant focused. Indeterminate tomatoes grow one truss of fruit at a time, so if we allow the plant to branch out too much, it will spend more time and energy growing leaves and stems. And then on those new stems even more new trusses, rather than ripening the fruit it’s already produced. And in our shorter Scottish growing season, that can mean the later fruit never ripens.
These are bush types like ‘Roma’, and with these, we leave the side shoots alone. These varieties are shorter, more compact, and tend to produce most of their fruit in a short window, almost all at once. If you prune them like a vine, you’ll drastically reduce your harvest.
Scottish weather is rarely consistent, and that can be tricky for tomato plants. One week it’s torrential rain, the next it’s dry and windy. Tomatoes don’t enjoy this unpredictability, especially when it comes to water.
Too much water all at once, particularly after a dry spell, can cause the fruit to swell very quickly and then split. It can also dilute the flavour, leading to tomatoes that are a bit bland and watery. So to try to control this, try to water evenly and consistently and don’t let the soil dry out completely between waterings.
If your plants are outside, it can help if you can provide some shelter from heavy rain. Even a bit of clear plastic sheeting or a makeshift canopy can do the trick.
In hotter spells, use mulch, like a layer of straw, compost, or bark chips to help the soil retain moisture and regulate temperature. I personally use straw, but do make sure it’s actual straw and not hay. Some shops sell hay labelled as straw, and hay often has seeds which can introduce weeds to your beds or containers.
Tomatoes are hungry plants. If you’re growing in the ground or a raised bed, adding fresh compost to amend your soil each year should give them everything they need.
If you’re growing in pots or containers, you’ll need to feed regularly. For this, I always begin feeding as soon as the first flowers appear. I use a standard tomato feed (high in potassium or labelled as “high potash”) in the water each week. Remember to always follow the dosage guidance on the packaging, NEVER add extra.
If you start noticing tomatoes developing black, sunken patches on the bottom, you’re likely dealing with blossom end rot. It’s often assumed this is caused by a lack of calcium in the soil, and while that is technically true, in almost all cases the real issue is inconsistent watering, and nothing to do with the soil.
Tomato plants need steady access to water in order to absorb calcium properly. If the soil dries out too much and then gets a sudden soaking, the plant can’t take up nutrients efficiently, even if the soil itself is good. So keeping your watering consistent - not too dry, not too soggy - is the key to preventing blossom end rot. It’s not a disease, just a physiological problem, and it usually clears up once the watering is sorted.
Blight is the one that causes the most worry for folks and is caused by a fungus like organism, hence it usually takes hold of plants that are in moist warm environments. There are actually two types of blight, caused by different organisms.
This appears as dark spots on the lower leaves, often surrounded by yellowing. This is more common in the hotter, summer months and can often be delayed by removing any leaves you see that have been affected. If you spot blight, do act fast to remove affected leaves and dispose of them, remember to clean your hands, pruners etc. before you use them again on any other plant.
This is more common in the damp, cooler conditions of late summer and autumn. It spreads quickly and affects the leaves, stem, and the fruit, turning them brown and mushy. One you identify late blight, harvest any fruit from the plant and use it quickly before the disease develops and ruins the fruit, then cut down and destroy the plants.
Although there is some debate about reusing the soil where infected plants have been grown, or composting the affected plant material, general advice advises against composting the plant material, as well as rotating crops to prevent repeat infections from soil.
You are more likely to be affected by blight on outdoor-grown tomatoes. Those grown in the greenhouse tend to have a degree of protection from airborne spores but you can take action to reduce the risk by:
● Pruning heavier, bushier plants to allow good airflow, which allows the leaves and stems to stay dry.
● Watering at the base of the plant and avoid splashing the leaves. Keep leaves dry whenever possible to prevent spores from splashing up from the soil.
● Removing any leaves that show signs of disease early.
As we move through June, keep an eye on the fruit beginning to form. Soon you’ll start seeing the first signs of ripening and I promise you, if this is your first time growing your own tomatoes, you are about to taste THE BEST thing you have ever grown and you will be buying more seeds and varieties for next year before you even realise it.
Next time, we’ll talk about:
• Continuing to manage plant health through peak fruiting.
• The big season end prune to help the plant focus on ripening.
• Harvesting.
• What to do with stubborn green tomatoes.
Until then, keep an eye on your jungle, don’t forget to prune, and make sure those plants have the support and feed they need to thrive.
Eli Appleby-Donald, one half of 'In the Garden With Eli and Kate' tends a productive urban garden in East Lothian. She considers herself a perpetual learner gardener, and has spent the last 11 years learning by experience, success, and failure.
Eli is a University digital educator by day, and she put those skills to action and regularly vlogs about gardening on YouTube where she has hundreds of videos about her gardening journey and her top tips, as well as appearing as a guest on other channels worldwide.
You can find out more on the fun of creating your own suburban garden paradise on either her YouTube channel, website, instagram., or her chat on the Scotland Grows Show.