Why your vegetables are not thriving, and how to fix it

March 10, 2025

You've put the weekends in, the bed is planted, and what you've got is a row of small pale things that have stopped rather than grown. It's the most disheartening stage of a veggie patch and it's also the most fixable, because it's nearly always one of four things rather than some mystery about having a green thumb or not having one.

Work through them in this order, because soil sits underneath the other three.

1. The soil

Soil that's compacted, or starved, or that stays waterlogged after rain will hold a plant back no matter what you do above ground. There's a quick test you can do standing in the bed. Grab a handful of damp soil and squeeze it. If it forms a hard lump that won't break when you poke it, there's too much clay and not enough organic matter in there. If it falls apart the instant you open your hand, it's too sandy and it isn't holding anything.

Both are fixed the same way, which is organic matter, and plenty of it. Compost and aged manure dug through the top 20cm will change the structure of a bed within a season. If the bed has been growing heavy feeders for a while it's probably also flat out of nitrogen, and a pelletised fertiliser will sort that faster than compost will.

A soil test kit is worth the small outlay before you start adding things, because pH decides whether the nutrients already in the soil are available to the plant at all. There's no point feeding a bed that's locked up.

2. The watering

Too much water and too little water look almost identical from the path, which is why this one catches people. Push a finger into the soil. If the top few centimetres are dry, water. If it's still damp down there, leave it and check again tomorrow.

The pattern matters more than the amount. A long soak twice a week wets the whole root zone and pulls roots downward. A light sprinkle every evening keeps the roots sitting in the top couple of centimetres where they cook on the first hot day. And water in the morning where you can, so the leaves dry off during the day rather than staying wet all night, which is where a lot of fungal trouble starts.

3. The sun

Most vegetables want 6 hours of direct sun a day, and fruiting crops like tomatoes and capsicum want more than that. If the plants are leggy and pale and reaching sideways, they're short of light.

Down here the sunny aspect is north, so a bed against a north facing fence gets the most of it and a bed on the south side of the house is in shadow for a lot of the year. If the only spot you've got is shaded for half the day, plant to suit it. Lettuce, silverbeet, spinach and most of the leafy greens will do fine on 4 hours. Tomatoes will not.

4. The timing

This is the one nobody suspects, and it's often the whole answer. A warm season crop sown in the middle of winter sits there and sulks, and a cool season crop sown into summer heat bolts to seed before you get a feed off it.

Broadly, the cool season crops go in from about March through to July. That's your brassicas, peas, broad beans, onions, spinach and most of the root crops. The warm season crops wait until the frost risk has passed, so from about October, and that's tomatoes, capsicum, cucumber, zucchini, pumpkin, beans and corn. Carrots and lettuce will go in through most of the year, with spring and autumn being the easiest.

Check the back of the seed packet before you sow, because the sowing window is printed right there and it's the single most ignored line in gardening.

5. And if it's none of those, look for pests

Holes in leaves, plants vanishing overnight, or a sticky coating on new growth all point at something eating the crop. Turn the leaves over and look along the stems, because most of what does the damage sits underneath where you won't see it from standing height.

Caterpillars and snails do the visible damage and aphids do the slow kind. Small flowers planted near the bed, like alyssum or marigolds, bring in the insects that eat aphids for you, and a good look under the leaves twice a week deals with most of the rest before it gets away from you.

Shop related products

Manutec Soil pH Test Kit. Tells you whether the bed can actually use what you are feeding it.
Brunnings Ultimate Garden Soil 30L. Bagged soil for lifting a bed that has run out of body.
Naturally Good Cow Manure 25L. Aged manure to work through before planting.
Neutrog Rocket Fuel 6kg. A quick lift for a bed that has stalled part way through a crop.

Did you know we also stock loose vegetable seed by the variety, seed raising and potting mixes, and soil moisture meters in the shop. They're not all on the website, so give us a ring on (08) 8536 4333 to check what's on the shelf, and the whole range is in the garden centre if you'd rather come and have a look. Bring a photo of the plant and we'll work out what's going on with it.