Heading Into Autumn: 3 Growing Mistakes to Avoid

Autumn has well and truly arrived and there’s a slight bite in the morning air which reminds me that winter isn’t far away. With a tropical low over the North Island at the moment, and I ever so reluctantly stuck indoors, I thought it would be a great time to cover some of the common, general mistakes gardeners (myself included) make when trying to grow challenging subtropical plants in NZ. 

1. Overwatering and Root-Rot 

As temperatures drop, plant growth slows and so does water uptake. Continuing summer watering habits into autumn and winter is a very common mistake that often leads to root-rot. It’s important to reduce watering during the cooler months substantially, allowing the soil to dry between watering. At the Nursery, we dial our watering right down to around once a month (if even that) for our greenhouse plants. Plants planted outdoors generally aren’t watered at all until temperatures begin to warm up again in September or October. In winter, slightly drier soil is always safer than consistently wet conditions. Root amendments (see our previous blog!) are also a great tool to help prevent soil-borne pathogens from settling in, so applying these in a water-soluble form now (if you have not already) can help set plants up well for the cold season ahead.

2. Not Taking Extra Care in the First Few Years

Young subtropical plants are far more sensitive to cold than established plants. Generally speaking, for the first two to three years many subtropicals are still developing root systems and adapting to local conditions. Providing protection during this period can dramatically improve long-term success. This might include frost cloth, temporary wind protection, or planting near a warm structure such as a fence or wall. A thick layer of hardwood mulch around the base helps insulate roots and can also act as a moisture buffer, by absorbing water and preventing the soil from staying overly wet. Similarly, in summer, some plants will benefit from shade cloth to reduce light stress and consistent watering to keep soil moisture stable. Once established, many plants will become much more resilient and will not require such a high degree of protection, but the first few years is when care is most important. 

3. Poor Plant Selection for Your Region

Not all tropical or subtropical plants are suited to every part of New Zealand. While it’s tempting to try growing highly tropical species, some are simply not practical outside warm, protected environments. For example, attempting to grow cacao outdoors in much of the South (or North!) Island is unlikely to succeed. Choosing plants that can tolerate our winters will lead to better results. Subtropicals such as Neem, feijoa, loquat, hardy bananas, and certain papaya varieties can perform well when given a more marginal climate. Realistically matching plant selection to your local climate (and to the microclimates you can create) is important to ensure success rather than disappointment.