Are you picking plenty of tomatoes this season? If not, take heart in the fact you’re certainly not the only one. A lack of fruit set – when flowers fail to produce fruits before they wither and drop – is one of the most common complaints among tomato growers. It’s frustrating and it’s not fair, particularly given all the attention you’ve no doubt lavished on your plants to get them this far.
Whether you’re yet to pick a solitary tomato, or your plants have abruptly stopped producing, the reasons behind the lack of fruit are often predictable and easy enough to fix. So don’t despair – read on and see if your plants can be persuaded to behave.
1. Insufficient Pollination
The first thing to consider is how easy it might be for pollinating insects to reach your crops. Tomatoes are self-fertile, which means each flower can pollinate itself. Nevertheless, the presence of bees and/or wind dramatically improves pollination by nudging the flowers just enough to help dislodge the pollen from the stamens.
Bumblebees are especially good at this. As they contract their flight muscles (a process called 'buzz pollination') these low vibrations literally shake the pollen free, allowing it to drop down onto the stigma – the female part of the flower that catches the pollen.
If you’re growing tomatoes in a greenhouse or polythene tunnel it may be worth considering whether pollinating insects have ready access to the plants. Open up doors and vents, which will also help to create a good through-flow of air, keeping plants cooler and reducing the risk of disease.
You can artificially pollinate tomatoes by lightly shaking the plants yourself to mimic the bee’s buzz. Twang string-lines or canes supporting vining tomatoes, or lift and drop (gently, from a very short distance!) container tomatoes.
2. High Heat Levels
In hotter climates, high temperatures can sometimes play havoc with pollination. Hot spells, when daytime temperatures remain above 30ºC (86ºF) and, crucially, nighttime temperatures fail to dip below 24ºC (75ºF), have the undesirable effect of turning pollen sterile. Turns out tomatoes like it hot – but not too hot!
The only thing you can do during a heat wave is bide your time. In the meantime keep plants well watered and healthy, so that when temperatures finally subside they’ll be in an excellent position to ramp up production once more.
Don’t forget that different tomato varieties are suited to different climates. If you’re in a hot part of the world, grow a heat-tolerant variety that is recommended for your region.
An added complication is humidity, or lack of it. Very high humidity can clog the pollen, so it’s unable to drop, while in very dry climates flowers may become so parched that pollen fails to stick and simply rolls straight off. In this instance regular watering may help to raise the humidity around the plants just enough to improve conditions.
3. Not Enough Fertilizer (or the Wrong Type)
The final factor to consider is soil fertility. Are your tomato plants getting the nutrition they need to grow plump, tasty fruits? Even if you have rich soil, from the moment the first flowers appear you should be feeding your tomatoes with an organic fertilizer that’s high in potassium, or potash. Potash helps promote flower initiation, and hence fruit production.
Keep tomatoes fed with an off-the-shelf tomato fertilizer or make your own high-potash liquid fertilizer for free. Every garden should have a clump of comfrey for home-brewed fertilizer.
Once you’ve done all you can to improve conditions, you’ll just have to be patient and wait for Mother Nature to do the rest. Don’t lose heart because the situation is bound to improve. When it does, the tomatoes will come thick and fast, and then you’ll be wondering what to do with them all!