Tomato Growing Problems

The 2013 tomato taste tests at the Adelaide Botanic Garden brought out throngs of tomato connoisseurs, but among the tomato tips and chat about favourites was a reoccurring theme of poor yields and crop failure.

Yields from field grown tomatoes vary with season and region and, as we were experiencing a pretty good crop at Heronswood, we were left wondering what was occurring in South Australia, and if their problems were unique to the area. Although not everyone has the same problems as Adelaide we can use it as a case study to highlight how to diagnose problems in your own patch.

Jan, from our Adelaide Garden Shop, points to heat and low humidity as the culprits. Heat stresses tomatoes; they typically wilt as they struggle to balance water uptake with water loss during very hot days. However a less understood impact is that flowers drop and fruit set aborts when temperatures exceed the ideal growing range for extended periods (e.g. days above 29°C and nights above 21°C).

Humidity also plays a two part role. Tomatoes like 40-70% humidity, for although we tend to think of high humidity as bad (it facilitates the spread of moisture borne diseases such as fungi), it can also be problematic when it is too low.

Air moisture is required to help pollen stick to the stigma and to allow flowers to pollinate, while some major pests, such as two-spotted mites, thrive and become a serious problem in drier conditions. So climate and season play a significant role in vegetable production, but how does knowing this help you?

If you can identify the issues you are dealing with you may be able to either prevent or treat resulting problems.

♦ Observe your plants for symptoms and/or pathogens. Photos or notes may help ensure you remember exactly what you observed.

♦ Online searches or an Australian specific disease reference book will help identify most common issues. We've also provided some tips below. Think plant and soil, and consider diseases, nutrient levels and pests.

♦ Identify the conditions that support the problem.

Can you change these or do you treat the symptoms?

♦ Plant tomatoes a metre apart. This improves airflow and minimises physical transfer of pests and diseases between plants.

♦ Try not to grow tomatoes in the same soil each year. Rest beds for 3-4 years before replanting with tomatoes or bio-mustards can be used to reduce the presence of harmful microbial activity by fumigating the soil after a tomato crop.

♦ Prune on low humidity days to reduce fungal diseases in open wounds.

♦ Clean pruning tools between plants (hand sanitising lotion or methylated spirits will do the trick).

♦ Never compost diseased plant materials as this may spread pathogens around the garden.

♦ Mix up your plantings. Many pathogens are host specific (e.g. they only feed off one species or family of plants). Interspersing beds with other species can provide physical barriers or regions without food that can prevent or slow their spread.

♦ Use companion planting. Planting marigolds around tomatoes suppresses nematodes which damage tomato roots.

♦ Identify a few good varieties that are best suited to your area and grow them well, rather than expending your energy and resources on lots of poor yielding plants.

Tomato breeding often focuses on cultivars which withstand cooler temperatures (allowing for a longer productive life), however heirloom varieties do vary in tolerances, so if you know your region has a specific challenge you may be able to find something suited to your site.

By growing a range and collecting seeds from the healthiest and best yielding varieties in your own garden you can develop a seed bank suited to your specific conditions.

So, on reflection, the problems experienced in Adelaide were probably both seasonal and specific (although doubtless not unique) to the area.

In the long term we may need to collect seeds and breed varieties specific to our conditions (maybe we’ll end up with region specific Australian heirloom tomatoes) but for now, by understanding the problems we face, we can address them and still have successful crops in what can sometimes be a challenging climate.