Growing tomatoes – what went wrong?

Have blemishes and disorders affected your tomatoes this season? While pests and diseases are often to blame for tomato disorders, the weather’s silly shenanigans, poor gardening practices, and even the tomato variety itself may cause skins to split, become blotchy, or develop sunken black spots. Here’s a guide to common tomato disorders and how to prevent them next time round.

Cracked skin

Concentric or radial cracks around the stem end and along the sides are caused by a sudden increase in water levels. When the plant suddenly receives a good deal of water following a dry spell, the fruit cells rapidly expand and burst, causing the skin to split. Certain cherry tomato varieties, such as ‘Sweet 100’, are prone to cracking. Too much nitrogen also causes skins to split.

Prevention

Keep the soil evenly moist. Mulching will help prevent soil from drying out.

Blotchy tomatoes

Blotchy ripening is often caused by a combination of shade and cool temperatures followed by bright sunny weather. It may also be caused by a potassium deficiency. You’ll first see light green or brown blotches on the green fruit. As the fruit matures, these patches gradually turn yellow while the rest of the fruit reddens, resulting in uneven ripening. When cut open, the fruit walls are sometimes dark brown.

Prevention

Feed with a specific tomato fertiliser, which is high in potassium, and remove excessive leaves to allow light through.

Blossom end rot

Irregular watering is usually the cause of blossom end rot, a disorder that causes sunken, blackish-brown areas at the bottom (blossom end) of the fruit. While blossom end rot generally indicates a calcium deficiency, it’s likely to be caused by irregular watering or sudden fluctuation in water levels, as lack of water prevents the mineral’s uptake. Acid soils and damage to roots can also prevent proper uptake of calcium.

Prevention

Keep the soil’s pH around 6.5.

Water regularly and evenly and mulch to conserve soil moisture. Feed with a specially formulated tomato fertiliser that should have all the nutrients tomatoes need.

Some tomato varieties are more susceptible to blossom end rot than others. Grow several different varieties and take note of which grow best.

Misshapen fruit

Wacky shapes can be the result of poor pollination or insect damage at the early stages of fruit development. Pollination problems may occur when temperatures are low and skies are cloudy, a combination which interferes with the growth of the pollen tubes and normal fertilisation.

Prevention

Grow tomatoes in a warm, well-lit area. Protect from cold in the early stages of growth.

Catfacing

Catfacing is a term that describes misshapen fruit with scars and cavities on the blossom end. It’s caused by the abnormal development of the flower bud before opening, which is often due to low temperatures when plants are young. It occurs most often on the first fruits formed, when temperatures are lower in spring, and again in autumn when temperatures drop, if plants are still setting fruit. Excessive wind and high nitrogen soil levels may also damage blossoms.

Prevention

Plant later in the season and shelter plants from wind and cold.

Avoid high-nitrogen fertilisers.

Puffiness

Puffy fruit with little internal gel is caused by incomplete pollination, usually due to high or low temperatures. When daytime temperatures rise above 37degC or nighttime temperatures dip below 12degC, seed doesn’t set properly. High nitrogen and low potassium also causes poor pollen formation, resulting in puffiness and a lack of normal gel.

Prevention

Plant later in the season, or protect from cold early in the season (a cloche or tunnel house is ideal). Where temperatures are blistering hot, use a shade cloth to protect plants from the midday sun.

Use specially formulated tomato food, which is low in nitrogen and high in potassium.

Green shoulders

Green or yellow shoulders that remain hard are the result of exposure to high temperatures and direct sunlight. Normally chlorophyll breaks down as the fruit ripens, but in some tomato varieties, during high temperatures, it fails to do so. This is fairly common with heirloom varieties.