Sunday, July 20, 2025

Try These Tomato Tricks

In Tasmania the first half of the season (Sep-Dec) is often too cool and cloudy for tomatoes to really prosper. The tricks below will help make your tomato plants more resilient, healthy and productive in our fickle climate.



Temperature

To perform well, tomato plants need permanent air and soil temperatures of between 20 and 25 degrees Celsius. I said ‘permanent’ and I meant it. This is hard to achieve in Tasmania.

In Tasmania, sowing tomatoes early (July, August) and then planting them outside in September or early October is really not the way to go.

When soil temperatures go below 10 degrees Celsius, tomato plants stop growing. When temperatures go back above 10 degrees after that, it takes some time before growth resumes.

In Tasmania simply don’t plant your tomato seedlings in your garden in September or October. Wait until the weather becomes consistently warmer. In most years this will be in November, but there have been La Nina years when it only really became warmer in December.

If tomato seedlings are becoming too large for the little pots you sowed them in, repot them into larger pots and keep them in a warm light spot until temperatures improve consistently.

Planting tomatoes in large black plastic pots that raise the temperature of the soil held in them, rather than in the cold ground outside, can be a really good trick. Black plastic pots in a sheltered or warm spot like a hothouse is even better.

You can sow tomatoes until late-December and have ripe fruit before the season ends (I have done it, it works!), because the second part of the Tasmanian season (Jan-Apr) is nearly always warmer, sunnier and more stable.

Experts recommend that you plant your tomato seedlings deeply, so their first adult leaves are just below soil level. This allows the plant to form more roots. That is good advice. But if you insist on planting your tomatoes outside in September or October, planting deeply will slow them down, as the soil at the bottom of planting holes will be cold.

Mulching the soil around tomato plants early in the season keeps that soil cool, so it is not recommended.


Water

Tomato plants do best if, once a day, every day, they receive a moderate amount water that is around the same temperature as the surrounding air.

Water from below, because wet leaves are more susceptible to mildew. Irrigation lines with sprayers or drippers connected to an irrigation timer is an ideal setup.

In spring tap water is often cold. To get around this, fill a watering can with water, put it somewhere where the temperature is slightly warmer (your hothouse?) and irrigate with that water the next morning. Repeat! And repeat!

It is best not to water tomatoes with a hose as soil with spores and bacteria may splash up from the ground surrounding the tomato plant resulting in their transfer to the plant.

A tomato plant suffers from Blossom End Rot when the pointy end of one or more of its tomatoes goes brown. The reason is that the plant is not able to absorb enough calcium, NOT because there isn’t enough calcium in the soil (most soils contain ample calcium), but because of insufficient and irregular watering.


Companion plants

Interplanting tomatoes with flowering plants of any kind will attract insects and make a major difference in terms of pollination.

Marigolds are particularly good as they attract insects and release a toxin that kills and inhibits hatching of nematodes. You could plant Marigolds as a cover crop and then interplant them with tomatoes. There is some scientific evidence that Marigolds are also a biological control against Whitefly.

Other good companion plants are Basil and Oregano because their smell distracts leaf-eating insects such as Whitefly.


Fertilising Tomatoes


Nitrogen - Once you have transplanted your tomato seedlings, don’t fertilise them with nitrogen-containing-substances, as this will encourage plants to form a lot of stems and leaves, instead of flowers and fruits.

Potassium - Sulphate of Potash, also known as potassium sulphate, promotes strong root development, enhances flower and fruit production, improves drought resistance, and strengthens plant immunity against pests. Once a fortnight, give each tomato plant one teaspoon of Sulphate of Potash dissolved in water, either on its leaves or on its soil. Sulphate of potash, although fairly harmless, is not organic

Calcium - Healthy food garden soils contain plenty of calcium, so in most cases it isn’t necessary to add calcium when growing tomatoes. However, if you are not sure about your soil, or if its pH is below 6, or if it is sandy, then adding cooked and then crushed egg shells to the soil where you are going to plant tomatoes can help. This egg shell mix takes a long time to break down, so add it to the soil a number of months before planting.



Pest Prevention without head aches!

Food Garden Group member Ross shared with me a recipe that a mate of his had recommended to improve the pest resistance of tomato plants. It didn’t sound credible, but Ross thought ‘there is no harm in trying’. He would like all Food Garden Group members to know about this recipe, because it really worked!!

Add 3 uncoated 300mg Aspirin tablets to a standard (9 litre) bucket of water. Mix thoroughly. When your tomato plants are past their young seedling stage, spray your them with this mix once a fortnight.

This mix substantially increases the tomato plant’s pest resistance capabilities. Why is this so? My research suggests that, when tomatoes are under attack by pests and diseases, they produce a hormone that is similar to the Salycilic Acid in Aspirin. This hormone puts the plant’s immune system into high gear, so it can ward off attacks.

By spraying an Aspirin solution on tomatoes and other members of the Nightshade family (potatoes, tomatoes, capsicum etc.) their immune system becomes fully ready to withstand pest attacks. The result, Food Garden Group member Ross found, is very healthy plants.

Worth mentioning:
  • Aspirin is not organic. There are recipes on the internet for making your own Salycilic Acid from Willow tree bark or Dandelion stems.
  • Watering with this mix is prevention. Tomato plants already affected by pests may respond, but this mix is not a cure.
  • Use uncoated Aspirin as coated Aspirin may clog up watering cans and sprayers.


Pruning

The more side branches a tomato plant has, the more effort it puts into forming leaves and stems. Pruning helps tomato plants focus on flowering and fruit. 

There are basically three types of tomatoes and they are pruned slightly differently:

  • Bush tomatoes (=determinate) don’t grow tall and produce most of their tomatoes around the same time. That can be handy if you grow tomatoes for passata. You don’t need to prune bush tomatoes if you don’t want to. However, Whiteflies may make their dense vegetation their home, so you may want to open up centres of bushes a bit to create ventilation. 
  • Vine tomatoes (= indeterminate) produce fruits over a longer period of time. Guide vine tomatoes to develop one or (at the most) two leaders. If you decide to have two leaders, allow the second leader to develop from a sucker low to the ground. Remove all other suckers. If a plant becomes too high prune away its top.
  • Cherry tomatoes are vine tomatoes, but pruning is a little bit different. Pinch out the first two or three side shoots, but then let the rest go and tie up. If the plant becomes too big, cut off its top and the tips of side branches.

With all tomato types, as seedlings begin to grow, gradually prune away their lowest leaves, especially ones that touch the soil, because pests and diseases may enter plants from the soil.



Fruit Development and Ripening

Once a tomato plant has flowers, it’s good to give it a little shake every time you check its progress. Tomatoes are self-pollinating and this motion, together with wind and insects, helps pollination.

Once a fortnight, give each tomato plant a little bit of potash and Aspirin mix (both were discussed above). You can mix them together in the same watering can, if you like. This will help fruit set.

When late in the season tomatoes ripen only slowly, you can help things along by cutting off the top of the plant and side branches if it has any, so that it will spend its energy to ripen its current fruit rather than on forming new stems, leaves and fruits.



May your tomato seasons be fruitful.

Max Bee


My sources for this blog post were:
  • My own experiences growing tomatoes over decades
  • FGG member Ross T.’s experience with lots of tomato varieties over many years
  • Tomato videos on the Gardening in Canada YouTube channel
  • YouTube video Transform your Tomatoes with this Household Ingredient by Next Level Gardening
  • YouTube video Tomato Growing Tips from a Real Nursery Owner by The Yorkshire Plant Nursery.

There are other posts about tomatoes on the Food Garden Group blog that may help you:
  • Early Tomatoes shows how some Food Garden Group members managed to have ripe tomatoes really early.
  • Blogpost Large Tomatoes on Show will help you select varieties that produce large tomatoes in Tasmania's climate.




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