Root-Zone Management in Outdoor Container Crops

With so many container crops in production this time of year, Dr. Josh Henry wanted to discuss keeping roots heathy when the weather is unpredictable.

PROBLEM: Field-grown container crops, including garden mums and fall container programs, are subject to fluctuating weather conditions such as temperature and precipitation extremes, making rootzone management especially critical for these crops. Excessive rainfall, nutrient leaching and disease pressure can cause plant stress, poor growth and crop losses.

_{Consistently wet substrate causes a dark green crust to form on the surface of the substrates.}

_{In mums, Fusarium can cause part of a plant to collapse.}

_{Heavy rains cause nutrient leaching, leading to deficiencies.}

JOSH’S TIP: When it comes to understanding the rootzone environment, remember: soilless substrates must balance the ratio of solid components (e.g., peat, perlite, bark) with air- and water-filled pore spaces—ideally around 50% solids, 25% air and 25% water.

Containers grown in the field are subject to adverse weather conditions, which can fluctuate throughout the growing season. Heavy summer rains are a major concern for growers, as they can leach nutrients and reduce the air-filled pore spaces, stressing the plants and making conditions more favorable for root rot pathogens to cause disease.

A proactive approach focused on maintaining healthy roots through disease prevention and irrigation and fertility management is your key to success. Here are three important processes to implement:

Stay Ahead of Root Diseases
• Wet, saturated conditions are conducive to root and crown rot pathogens—causing disease. Watch for low spots and improve field drainage.

• Develop a comprehensive fungicide drench rotation covering major pathogens like Pythium, Phytophthora and Fusarium. Utilize labeled fungicides, including strobilurins, thiophanate-methyl and etridiazole.

• Incorporate biological options that support root health. Some species of Trichoderma and Streptomyces are effective.

Manage Fertility with the Weather in Mind
Heavy rain can rapidly leach nutrients, leading to deficiencies. Fertilizing immediately after rain replaces low-EC rainwater with essential nutrients.

Consider a combination of controlled-release fertilizer (CRF) and water-soluble fertilizer (WSF) for consistent fertility. Incorporate a low to medium rate of CRF as a base to buffer against leaching and use WSF for quick corrections and flexibility. Note: Be sure to monitor EC and pH regularly to help make fertility decisions.

Avoid Irrigation Extremes
• Water based on crop needs and weather, not based on a timer. Check moisture using the 1-5 scale or by weight and let pots dry slightly between waterings to promote deeper rooting. Aim for a 15% leaching fraction (LF).

• Reduce irrigation after rain to prevent excess saturation, and consider the forecast to decide if watering is necessary.

• Prioritize morning irrigations to reduce wet foliage and humid microclimates in the canopy.