tomato guide 4 : watering, fertilising and protection from pest and disease

tomato guide: watering, fertilising & protection

The warm weather should have our tomato plants growing big and wild! Make sure you are watering deeply and early, especially on those hot windy days, the plants can’t take up any precious nutrient you’ve so diligently added to the soil unless the soil is moist. 

If you’ve missed the mornings’ water it’s ok to water in the heat, especially if you notice your plants wilting badly; otherwise you’ll risk not having any live plants to water at all! If you haven’t mulched when planting then apply some pea straw, lucerne or sugar cane mulch to reduce moisture loss. 

Avoid watering the leaves as much as you can as excess moisture can lead to mildews and bacterial diseases. Drip irrigation under mulch is preferable to sprinklers because the water will be delivered efficiently to the roots and won’t splash the foliage. Wicking beds are great for ensuring your tomato plants have a steady supply of water over the summer months, but they can be problematic in heavy rain as the roots can stay too wet.

fresh green tomato foliage growth

If you haven’t planted with manure then top-dress with some slow-release organic fertiliser. At this stage you should see some fruit forming and lots of flowers. If you find your plants are putting on a lot of leafy growth and not many flowers a very small application of Sulphate of Potash will provide your plants the potassium they need to flower and set fruit. Seaweed solution or homemade banana skin tea also contain potassium so apply fortnightly and it should improve your yield.

Dolomite lime can help if you find your soil has become too acidic from adding compost or manure (check the pH with a simple soil test kit or bring some soil into the nursery and we can test it for you). Lime will also provide calcium which helps prevent blossom end rot, more on that later. Fish emulsion, worm juice, or comfrey/weed tea once a fortnight will turbo-charge your plants. These fertilizers are in liquid form and are taken up much more quickly by the plants.

Many gardeners get caught up trying to diagnose a problem with their tomatoes, searching for a solution that comes in a convenient spray bottle. More often than not the problem is due to inconsistent or improper watering or feeding. Encouraging beneficial insects to the garden by planting lots of flowers of different sizes will help create a self-sufficient ecosystem and guard your plants against pests. Aphids will be gobbled up by lacewings and ladybirds and their larvae; caterpillars eaten by assassin, damsel and shield bugs; and spiders should take care of the rest! If you want to keep out bugs in general use insect-proof netting. 

Bear in mind: this will keep out pollinating insects as well so don’t forget to shake your tomato flowers every so often; the vibration should be enough for pollen from the male parts of the flower to drop onto the female parts. Netting will also prevent birds from pecking fruits and possums from stealing them, but if you have rats you’ll need to use chicken wire mesh and dig it into the soil. Don’t be fooled by ‘natural’ packaging on products like tomato dust; they may be made from plant extracts but they have proven toxicity to humans and wildlife.


In Melbourne plant anywhere from March to the winter solstice. Plant an early variety like Tasmanian Purple for an early harvest. Garlic takes about seven or eight months to grow so make sure you are willing to dedicate part of your garden to it for that long. Plant in a full sun position with the cloves pointy-end up about 10-20cm apart. They should shoot through in about two weeks.

1. Early Blight aka Target Spot

Look for dark brown patches surrounded by yellowing, sometimes in concentric circles, or ‘target’ shapes. These start on the older leaves and move up the plant. Fruit may have sunken yellow or brownish areas appear near the stem.You’ll probably get less fruit too, and what there is may be damaged by sun scorch due to the lack of healthy foliage to shield the fruit.

This is a soil borne fungal disease. Like most fungal problems, it loves warm, moist conditions, meaning a rainy summer or lots of overhead watering will increase the likelihood that your tomatoes get it.


  • Use under-mulch drip irrigation or water at the base of the plant
  • Stake your plants and prune lower side branches so that no parts of the plant are touching the ground.
  • Aim for good air circulation by spacing your plants generously.
  • Mulch thickly with a straw mulch to prevent fungal spores in the soil being splashed onto your young plants.
  • Rotate your crops so that fungal spores in the soil have become inactive by the next time you plant tomatoes in that spot.
  • If you already have Early Blight, remove and dispose of any affected leaves or fruit as soon as they appear.
  • Spray the leaves with dilute seaweed solution, or eco fungicide once a week.
2. Blossom End Rot

The blossom end (the part of the tomato on the OPPOSITE side from the stem) develops a small water-soaked spot that enlarges and turns blackish brown and leathery. This usually happens when the fruit is about half ripe. Essentially a problem of the plant not being able to take up enough calcium from the soil. This means that this problem is not a ‘disease’ that can be passed from plant to plant or fruit to fruit, and cannot be sprayed for! The great news is when you get the watering right the problem goes away so you can just take off affected tomatoes and wait for new fruit to form.

In MOST CASES there is actually enough calcium in the soil, but the plant can’t use it due to dry roots or waterlogged or underdeveloped roots. This is most often due irregular watering – i.e missing a day or three, then drenching the plants to make up for it. This has much bigger effects if you tomatoes are in pots, raised beds or sandy soils, as the soil can dry out very quickly in these situations. It can also be due to very soggy or heavy soils, where the root system can’t grow through the sticky clay or is drowning and rotting off, meaning there aren’t enough roots to collect the calcium.

More rarely there is actually a calcium deficiency, but before assuming this get into the habit of checking that your soil really is moist when you assume it is by the highly scientific method of wiggling a finger right down into it.


  • Prepare your soil well with compost or well-rotted manure so that it holds moisture, and mulch it.
  • Keep soil moisture consistent – which means checking how deeply any rain has penetrated (it can have scarcely wet the soil) and checking if you need a second water at the end of very hot or windy days.
  • If you have had this problem before despite perfect watering regimes, add a dusting of garden lime to your soil before planting.
  • Plant cherry tomatoes, which are less susceptible.
3. Wilts

This problem occurs most in cooler seasons, later in the growing season, and in a dry spell. It is caused by a fungus in the soil, which enters through root hairs and travels up through the stem, causing foliage to yellow, starting at the base of the plant and moving upwards. This yellowing often appears as a V-shaped section near the tip of the leaf. The yellow foliage then turns brown, and dies – whole branches may die, although the top of the plant will usually continue to grow healthily but more slowly than in an uninfected plant. The leaves may wilt during the middle of the day.

The fruit on the affected branches will mostly drop before it is ripe, or be sunburnt due to the lack of protective foliage. Even fruit on healthy branches will be often be small and with yellowing on the ‘shoulders’. The stem looks healthy from the outside, but will show brown discolorations if cut.


There is nothing you can do once you have this wilt for the plants of the current growing season, however preventive measures include

  • Maintain good drainage and healthy soil.
  • Plant wilt-resistant tomato varieties such as Roma or Burnley Surecrop.
  • If you have had wilt, don’t plant members of the solanum genus in the infected area for at least 3 years, ideally 5. The fungal spores are very persistent in the soil, especially in cooler areas.
4. Tomato Grub aka Tomato Fruitworm (Heliothis ssp.)

The larvae of a small brown moth (approx 3-4cm wingspan), which flies at night and lays pinhead-sized white spherical eggs on the tomato leaves. Green or brown, lightly striped caterpillars hatch, which will eat leaves, stems and buds, but mostly burrow into fruit to feed. The entry hole may be small if the caterpillar is still young, but becomes larger as they mature (to approx. 4cm). At this stage they will migrate into the soil and pupate about 10cm below the surface.


  • Check leaves for caterpillars and eggs regularly and squash.
  • Plant umbelliferous flowering plants such as coriander, dill and parsley, and allow them to flower. Also thyme and alyssum. These flowers attract the tiny wasps which parasitise the heliothis The eggs will look brown or black if they have been parasitised.
  • Remove any fruit that have entry holes, and drown in a bucket for several days before composting or putting in your worm farm.
  • Cultivate the soil in winter keeping an eye out for pupae, and destroy.
  • Dipel (Bacillus thuringiensis) will kill Tomato Grub, but it is safe once inside the fruit, so this is not a particularly effective strategy.
5. Bacterial Spot 

This bacterium can be present on the seeds of the tomato, or can enter through wounds or leaf stomata. It enjoys very humid warm conditions, particularly with warm nights. 

Small water-soaked lesions appear mainly on younger leaves, where they can be seen most easily from the underside. These enlarge, changing from green to purplish-grey with a black centre. The lesion tissues may thin and crack (leaving perforations in the leaf), and be surrounded by white or yellow colouring; leaves may then die and possibly drop. 

Fruit is usually unripe when infected, and shows dark raised specks that progress to being brown and sunken. This damage seldom leads to rot, so the fruit remains useable if skinned.


  • Practice crop rotation
  • Don’t leave chilli’s or Nightshades growing over winter if your tomatoes were infected, as these may harbour the disease.
  • Use under-mulch drip irrigation or water at the base of the plant.
  • Aim for good air circulation by spacing your plants generously.
  • Use disease-free seed stock
  • Clean secateurs with methylated spirits or eucalyptus oil to sterilize the blades if you are pruning and think you may have some infected plants.

Other problems you may encounter are root-knot nematode, whiteflies, powdery mildew, and leaf curl viruses. Practicing crop rotation (don’t grow tomatoes or other Solanaceae in the same soil year after year), encouraging beneficial insects, and watering consistently (soil, not the leaves!) should help you protect your tomato plants against the onslaught of problems. They are sensitive little petals but often still fruit well despite suffering pest and disease damage.

If you are lucky enough to have tomato seedlings pop up out of your homemade compost transplant it to a sunny spot and enjoy the rewards! Self-seeded tomatoes are often the hardiest; they will most likely be cherries unless you have added large-fruited varieties from last season to your compost.

Remember, tomato plants often look terrible once they grow up, especially towards the end of the season. They can’t be beautiful and delicious all at the same time! But we love them any way.


Corner of Roberts & Stewart Streets, Brunswick East, VIC 3057
(03) 9389 0111
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