It’s been just over a month since I planted out the last of my tomato seedlings into their final growing place. Most of them are outdoors in 10 litre pots, lining the paths of Plot 35a. Some are in a plastic greenhouse, with the chillies. My plot, tucked away in a sheltered spot in south London, is normally warm enough to grow tomatoes outside, but I am trying out a few under cover to compare their progress – particularly if late blight hits in the middle of August.

I started growing tomatoes 13 years ago, when I got my first flat with a garden in London. Since then I’ve tried pots, grow-bags and outdoor beds and found that those raised in pots have produced the most fruit. Growing in outdoor beds seems to leave the plants more susceptible to blight, while grow-bags don’t provide enough compost or nutrients to produce a good crop, despite what the packaging says.

I sowed 20 varieties, half of them heritage, back in March. Around 60 plants germinated, but quite a few were cut down by the surprise late frost in May – the latest I’ve ever experienced in London. I ended up with a total of 36 tomato plants which are now in vigorous health. You can read about the varieties I’m growing in this post from earlier this year, but I’m most looking forward to Yellow Pear, Pink Brandywine and Indigo Blue Berries.

The heatwave of last month, followed by a really good soaking of rain last week, has caused them to become really leggy and overly lush with shoots. Too much leafy growth means a tomato plant is not focusing on producing fruit. If you haven’t already done so, remove these side shoots – these are obvious when you look at the plant, as they will be the ones that are not bearing flowers or buds, just lots of leaves, and are often growing downwards just underneath a flower-bearing shoot.

You only need to remove side shoots with indeterminate or cordon tomatoes – which are the varieties grown up a cane or string suspended from the roof of a greenhouse. The vast majority of varieties are indeterminate. Bush or determinate varieties generally don’t need staking, although it helps to thin out a few of the non-flowering shoots to divert all the plant’s attention into fruit production. If you keep removing the side shoots and tying in the main stem to a bamboo cane, you’ll be left with a really strong cordon with hopefully a decent amount of tomatoes.

If tomato plants are starting to flower – and even those outdoors in the south of the UK will be by now – it is time to feed them. I use bought seaweed-based organic tomato fertiliser, such as Maxicrop, and my own plot-made comfrey tea. Both are rich in potassium to encourage fruit set and growth.

I have one large comfrey plant which is irrepressible. Every plot should have one – you just need to keep it in check otherwise it will spread out of control, if it is common comfrey – established plants have roots that can drill several feet deep below the surface. You can get Russian comfrey, Bocking 14, which is sterile and much easier to contain. When the plant starts to produce leaves in April I start cutting it back hard to the ground, and put the leaves in one of those small food waste bins that, crucially, have a lid that clicks and stays closed – this is essential to keeping the strong smell of rotting comfrey inside.

You could also use a plastic bucket, as long as it has a lid that stays on in all weathers. Keep cutting the comfrey back once it regrows – although at some point in early summer it will grow faster than you can make tea, and produce flowers which are loved by the bees, so maybe you can give it a break for a few weeks.

Squash the leaves in tightly, cover them with water, close the lid and leave it for 6-8 weeks. By then it should have produced a thin brown liquid, like weak tea. Strain the liquid using an old sieve or colander, and discard the spent leaves on the compost heap. Store the tea in old water bottles. This strength of comfrey tea – like weak black tea – will need to be diluted 1 part tea to 10 parts water.

The tomatoes will need a good drench of food once a week, as well as, if they’re grown in pots or bags, watering three to five times a week during hot dry periods. The first red (and yellow, and purple, and striped) tomatoes should be ready by the end of July. Watch out for blight, which is at its worst in August after heavy rain. If you’re growing in pots like me, make sure there’s enough space between each pot to let the air circulate around the plants.