3 Tips For Preventing Root Rot

Root rots like pythium, phytophthora and rhizoctonia are common diseases that attack young bedding plants in the spring and we often find ourselves treating prophylactically or curatively at some point during the growing season. These diseases have many sources, but plants that are stressed and over-watered are usually more prone to attack.

I recently took an informal poll of growers at a meeting to determine how many growers enjoy the task of “spot-watering” (checking each pot individually and watering according to that individual’s needs). Not surprisingly, no one confessed to liking the job.

“An ounce of prevention is worth a pound of cure” is how the saying goes, and it couldn’t be truer when we consider our greenhouse crops. We often think about preventative strategies like good sanitation and scouting to prevent disease and insect problems. However, the substrate, and how you handle the substrate, is an often-overlooked preventative measure to avoid production and disease problems later in the season. In most cases when we think about disease control and substrates, we want to focus on the physical properties, specifically the pore space and the water-holding capacity of the substrate.

Choose The Right Substrate

Let’s first consider the selection of your substrate. Substrate manufacturers have a multitude of products to offer us; it is our job to select the appropriate substrate for the scenario we are growing in. If we take a closer look at the substrates available to us, we will find dramatic differences between them. The obvious difference is the components that are used to create the substrate. Peat and perlite are the standard components, but we also have vermiculite, coconut coir, compost, rice hulls and bark, just to name a few.

To complicate the issue, each one of these can come in different grades or sizes that will also influence the pore space and water holding capacity. Generally speaking, the larger particle sizes in your substrate will facilitate drainage; therefore the opposite is true, the smaller particle sizes will facilitate water-holding capacity.

We can see this in Figure 1. After irrigation, the water has drained from each of the substrates and only the water that is held on the surface of the particles is left (blue outlines on the particles). The substrate on the left has smaller particle size, and by volume has more water than the larger particles on the right.

How can we use this knowledge to our advantage? Take note of the season, the crop and your irrigation habits. Choose a substrate with better drainage in cooler seasons, for crops that do not tolerate wet conditions, or if you tend to run your crops on the wet side. Conversely, in warmer seasons, crops that require a lot of water or if you tend to run your crops on the dry side, you may choose to use a substrate that has better water-holding capacity.

Different Pot Sizes Drain At Different Rates

The particle size is not the only influence on how our substrates drain. The pots we use can actually have a dramatic effect on substrate drainage. Taller pots drain better than shorter pots.

You can see in Figure 2 the percent of air, water and solids in an identical substrate in different sizes of pots. This phenomenon has more to do with the height of the pot than the diameter. As the pot increases in height, the ability of the substrate within it to hold water against the force of gravity decreases. Therefore, the taller 6-in pot drains better than a 4-inch pot and a plug flat will drain even less, the same way a standard pot will drain better than an azalea pot of the same diameter.

Now you may be thinking about that plug flat that doesn’t drain as well as other taller pots and how often you need to water plug trays, especially as the seedling matures. The rate of drying is not due to drainage, but to evaporation and the water uptake of the plant via transpiration, coupled with the relatively low volume of substrate. So yes, the plug flat might dry out faster, but it isn’t due to the rate of drainage.

Avoid Nesting Pre-Filled Flats And Pots

Many growers prefer to fill flats and pots prior to use. After the containers are filled, they are palletized and stored until they are needed.

When filled containers are filled and stacked, we run the risk of compaction due to pots nesting within each other (Figure 3). When the substrate is compacted, we have decreased or even eliminated the amount of air space in the pot, and air space means drainage. When a grower uses these pots, they will stay wet longer than non-compacted pots and increase the risk of root rot diseases (Figure 4).

The problem is accentuated because the pots on the bottom of the pallet are compacted more than the pots at the top. Once the pots are distributed on the bench, there will be vast differences in drainage and therefore, when they will need to be irrigated again. So begins the endless cycle of spot watering (Figure 5). It is acceptable to pre-fill pots and to stack them, just be sure to offset them or place sheets of plywood between layers to avoid nesting.

Take these simple concepts and apply them to your operation and you will surely be rewarded with healthy plants, a crop with less root disease and fewer frustrations from spot watering.


Leave a Reply

More From Uncategorized...
Seed Meets Technology

October 9, 2015

Seed Meets Technology Event Highlights Advancements In Vegetable And Bedding Plant Breeding

The second-annual event, held in The Netherlands in September, featured demonstrations, trial fields and presentations on green chemistries for seeds, hydroponics and phenotyping.

Read More

October 8, 2015

Industry Standards For Greenhouse Lighting On The Horizon

As the use of LEDs has risen among greenhouse growers, so have concerns about the best way to measure and compare the many LED light products across the market. As a result, the lighting industry is responding to a call for greater transparency and the development of standardized measuring and testing methods.

Read More
Delphinium 'Guardian Lavender' (Kieft Seed)

October 7, 2015

National Garden Bureau Names Four Crops For 2016 “Year Of The” Program

The National Garden Bureau announced four crop selections for its 2016 "Year Of The" program. New this year is the addition of a bulb crop class and a video created especially for the edibles class.

Read More
Latest Stories

June 25, 2015

Berger And Theriault & Hachey Peat Moss Form Strate…

A strategic alliance between Berger and Theriault & Hachey Peat Moss allows Berger to continue to meet its customers by ensuring the continuity of its Baie-Sainte-Anne and Bay du Vin facilities for the next 40 years.

Read More
2015 Top 100 Growers 75

May 1, 2015

2015 Top 100 Growers: Harts Nursery (No. 75)

Learn more about Harts Nursery, No. 75 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 71

May 1, 2015

2015 Top 100 Growers: Van de Wetering Greenhouses (No. …

Learn more about Van de Wetering Greenhouses, No. 71 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 71

May 1, 2015

2015 Top 100 Growers: Welby Gardens Co./Hardy Boy Plant…

Learn more about Welby Gardens Co./Hardy Boy Plants-Hardystarts, No. 71 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 65

May 1, 2015

2015 Top 100 Growers: Corso’s Perennials (No. 65)

Learn more about Corso's Perennials, No. 65 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 64

May 1, 2015

2015 Top 100 Growers: Bob’s Market And Greenhouse…

Learn more about Bob's Market And Greenhouses, No. 64 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 61

May 1, 2015

2015 Top 100 Growers: Armstrong Growers (No. 61)

Learn more about Armstrong Growers, No. 61 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 59

May 1, 2015

2015 Top 100 Growers: Nash Greenhouses (No. 59)

Learn more about Nash Greenhouses, No. 59 on Greenhouse Grower's 2015 Top Growers list.

Read More

May 1, 2015

2015 Top 100 Growers: Willoway Nurseries (No. 53)

Learn more about Willoway Nurseries, No. 53 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 51b

May 1, 2015

2015 Top 100 Growers: Henry Mast Greenhouses/Masterpiec…

Learn more about Henry Mast Greenhouses/Masterpiece Flower Co., No. 51 on Greenhouse Grower's 2015 Top Growers list.

Read More
2015 Top 100 Growers 51a

May 1, 2015

2015 Top 100 Growers: Rockwell Farms (No. 51)

Learn more about Rockwell Farms, No. 51 on Greenhouse Grower's 2015 Top Growers list.

Read More
Top 100 Growers No. 8

April 13, 2015

2015 Top 100 Growers: Color Point (No. 8)

Learn more about Color Point, No. 8 on Greenhouse Grower's 2015 Top 100 Growers List.

Read More

March 31, 2015

Manufacturers Are Taking Biologicals To The Next Level

Through acquisitions and new products, many crop protection companies are making firm commitments to the future of the biocontrols industry.

Read More
Aquaponics At Brogue Hydroponics

March 30, 2015

Aquaponics Is Making A Splash At Brogue Hydroponics

The owners of Brogue Hydroponics explain why they expanded into aquaponics, and how the shift has helped them uncover a new market opportunity.

Read More

February 11, 2015

Benchmarks: Find Your Game-Changer

Refuse to accept the status quo in your organization. Explore possibilities until you find what works best for your company.

Read More
Lychnis 'Petitie Jenny'

February 2, 2015

Variety Showcase: A Dainty Debutante

Lychnis flos-cuculi ‘Petite Jenny’ is a dwarf form of the popular Blooms of Bressingham® variety Lychnis ‘Jenny.’ This double-flowered little beauty was discovered by Paul Gooderham at Bressingham in a patch of its parent, ‘Jenny.’ ‘Petite Jenny’ produces masses of large, fluffy, double flowers like ‘Jenny,’ but with a more diminutive habit. The species goes by the common name “ragged robin,” but there’s nothing unkempt about ‘Petite Jenny’. An easy-to-grow, tidy little plant, it is suitable for any sunny or lightly shaded border and is also a good container candidate. Garden Performance Mass of bright pink double blooms beginning in mid-May. Sterile blooms provide a longer flowering period Erect, leafy flowering stems Forms compact, bushy clumps just 14” tall with an 18” spread Attracts bees, butterflies, hummingbirds and is deer-resistant Ideal for containers, front of borders, informal cottage gardens and as cut flowers’ Sun or part shade USDA Hardiness Zones 5 to […]

Read More

January 20, 2015

Register Now For Biocontrols 2015 Conference & Trad…

The first-ever conference, sponsored by Meister Media Worldwide and the Biopesticide Industry Alliance, March 3-5, offers hands-on, real-world technical advice on biocontrols to help you craft a “softer” pest management program focused on resistance management, MRLs and results.

Read More

October 6, 2014

Fighting Fall Foliar Disease: The Best Defense Is A Goo…

Managing foliar diseases starts with evaluating the greenhouse environment. Virginia Brubaker, GGS Pro Technical support supervisor for Griffin Greenhouse Supplies, shares some ways you can defend against fall foliar diseases.

Read More