Using Parboiled Rice Hulls In Substrates to Finish Greenhouse Crops

Fig. 1.  Growth and development of Impatiens ‘Dazzler Blue Pearl’ grown in substrates containing 20 percent perlite or whole parboiled rice hulls and (from L to R) 70 to 40 percent peat moss and 10 to 40 percent ground parboiled rice hulls after four weeks.

Have you considered replacing perlite with whole parboiled rice hulls (PBH) or peat with ground PBH in your growing substrate for finishing spring bedding plants, but are not convinced they are an effective substrate component? Alternative substrates are a hot topic, as many growers are looking for more sustainable growing mixes, lower production costs and superior performance. However, alternative substrate components do not have the history and popularity that peat moss or perlite may enjoy.

In the April issue of Greenhouse Grower, we shared the results of our work propagating New Guinea impatiens cuttings in substrates containing whole or ground PBH as replacements for perlite or peat moss, respectively. In this second article of the two-part series, we will share our most recent research examining how whole and ground PBH work for finishing seed-propagated bedding plants in the northern U.S.  

How The Study Was Conducted

At Purdue University (40 degrees north latitude), seedlings of Celosia ‘Fresh Look Gold,’ Impatiens walleriana ‘Dazzler Blue Pearl,’ Pelargonium ×hortorum  ‘Bullseye Scarlet’ (geranium) and Tagetes patula ‘Bonanza Flame’ (marigold) were transplanted into 4.5-inch plastic containers filled with a substrate composed of the following:

  • 70, 80, or 90 percent peat moss and 10, 20, or 30 percent whole PBH or perlite
  • 40, 50, 60, or 70 percent peat moss, 10, 20, 30, 40, or 50 percent ground PBH, and 20 percent whole PBH or perlite.  

The substrates with varying proportions of different components are outlined in Table 1. Peat-based substrates were mixed according to Table 1, and lime was incorporated at rates of 2.37 to 3.26 g•L‒1 based on the percentage of peat in the substrate.
The plants were grown in a double-polyethylene covered greenhouse from April to May with a temperature set point of a 70ºF day/night and a daily light integral (DLI) ranging from 22 to 27 mol•m‒2•d‒1. Plants were hand-irrigated as necessary with acidified water supplemented with a combination of two water-soluble fertilizers (3:1 mixture of 15–5–15 and 21–5–20 NPK respectively), to provide 200 ppm nitrogen. When plants flowered, the plant height and marketability was recorded. Root and shoot dry mass was determined after four weeks for impatiens and marigold, after five weeks for celosia, and after seven weeks for geranium. pH and EC readings were taken after three weeks for impatiens, geranium and marigold and after six weeks for celosia.

Table 1. Proportion of peat moss, perlite and whole or ground fresh PBH mixed in varying proportions (by volume) used for finishing bedding plants.
Substrate Component (percent)
Mix Peat Moss Perlite Whole Rice Hulls Ground Rice Hulls
Substituting whole rice hulls for perlite
1 90 10
2 90 10
3 80 20
4 80 20
5 70 30
6 70 30
Substituting ground rice hulls for peat moss
7 70 20 10
8 70 20 10
9 60 20 20
10 60 20 20
11 50 20 30
12 50 20 30
13 40 20 40
14 40 20 40

Substrates With Rice Hulls Produced Excellent Quality

Shoot dry mass (SDM), a measure of above-ground growth, was not influenced by any of the substrate components (peat, whole or ground PBH or perlite) for celosia, impatiens or marigold. However, SDM of geranium grown in 90 percent peat moss and 10 percent whole PBH was 72 percent lower than the other substrate treatments.  
Root dry mass (RDM) of celosia was significantly higher when grown in substrates containing peat and whole PBH compared to peat moss and perlite. Each crop responded somewhat differently to the varying proportions in the substrate. The proportions that produced the highest RDM for each crop are:

  • Celosia: 70 percent peat moss and 30 percent whole PBH (76 percent greater compared to peat moss and perlite)
  • Impatiens: 40 percent peat moss, 40 percent ground PBH and 20 percent perlite. (Fig. 1) However, RDM of impatiens was lowest when grown in a substrate containing 80 percent peat moss and 20 percent whole PBH.
  • Marigold: 70 percent peat moss, 10 percent ground PBH and 20 percent whole PBH or 40 percent peat moss, 40 percent ground PBH and 20 percent perlite.
  • Geranium: 50 percent peat moss, 30 percent ground PBH and 20 percent whole PBH or 50 percent peat moss, 30 percent ground PBH and 20 percent perlite.

The height of celosia, impatiens and marigold at flower was not influenced by any of the substrate components. However, geranium grown in 90 percent peat moss and 10 percent whole PBH were significantly shorter when plants grown in the other substrate treatments.

Substrate pH and EC values of marigold three weeks after transplant were not influenced by any substrate component. The substrate pH of geranium slightly increased when the percentage of ground PBH increased above 10 percent when measured three weeks after transplant and gradually decreased by week six. However, the EC of the substrate was not influenced by any substrate component.
In the study presented here, when a crop of celosia, geranium, impatiens and marigold was finished or grown-out in substrates containing a combination of peat (40 to 50 percent) and ground PBH (30 to 40 percent) both not exceeding 80 percent and 20 to 30 percent whole PBH, overall growth and quality was comparable or higher than the standard peat and perlite mixes.

Additionally, the importance of using peat-based substrates that contain components that allow adequate drainage, such as perlite or rice hulls, is highlighted in this study. For example, root and shoot dry mass and plant height were negatively influenced when peat moss exceeded 80 percent as the substrate remained excessively wet.
Reflecting on our collective results from experiments evaluating whole and ground PBH as substrate components for greenhouse crop production, it appears that whole PBH may be a suitable replacement for perlite, while ground PBH may be suitable replacements for peat moss for substrates used in both propagation and finishing of bedding plants.

The Results Are Encouraging
    Both whole and ground PBH appear to be viable alternative substrate components during finishing of bedding plants. Whole PBH appear to be a suitable replacement for perlite up to 30 percent and ground PBH appear to be a suitable replacement for peat up to 40 percent. Producers are always encouraged to conduct trials in their own greenhouse to determine what substrate mixes are most suitable for them as watering, species, cultivars and length of crop production may influence performance.

Leave a Reply

More From Crop Inputs...
Dallas Johnson Greenhouses

April 14, 2018

Kemin Forms Distribution Partnership With Plant Products

Under the agreement, Plant Products will be a Kemin Crop Technologies’ distributor in the northeastern U.S.

Read More
Basewell-cuttings-from-Dummen

April 13, 2018

Dümmen Orange Debuts New Rooting Technology

Basewell bare-root cuttings feature advanced root development and no growing media, which allows products to ship to growers from off-shore production locations, ready to transplant directly into the finish container.

Read More
Irrigation-feature

April 10, 2018

New Tool Helps Greenhouse Growers Analyze Irrigation Water Quality

The University of Connecticut and University of Florida have partnered to launch the WaterQual tool as part of the CleanWateR3 research program.

Read More
Latest Stories
lucas-greenhouses-plant-roots-growing-mix

March 18, 2018

New Soil Amendment From Kemin Promotes More Efficient N…

Valena, a soil amendment sourced from a proprietary strain of Euglena gracilis (algae) rich in beta-glucan, is designed to support the growth of healthy and strong plants.

Read More

March 13, 2018

Greenhouse Biocontrol Goes Mainstream

Biological control has moved into the mainstream for greenhouse growers. And the timing couldn’t be better, as consumer demands for more sustainable production methods for the plants they buy are moving back upstream.

Read More
Jose-Milan-Bayer

February 11, 2018

Bayer Has New Turf and Ornamentals Global Market Manage…

Jose Milan will be focused on helping growers deal with regulatory issues, while promoting the environmental benefits the ornamentals industry offers.

Read More
Belchim Crop Protection

January 24, 2018

Engage Agro Now Doing Business as Belchim Crop Protecti…

For more than 30 years, Belchim has been providing agricultural customers internationally, including greenhouse growers, with more than 100 well-known products.

Read More
cuttings-facility

December 13, 2017

New Webinars Address Effective Propagation Techniques

e-Gro, an online clearing house for alerts about greenhouse disease, insect, environmental, physiological, and nutritional disorders, recently posted two new propagation-related webinars on YouTube.

Read More

December 4, 2017

Raker-Roberta’s Young Plants Debuts as Roberta’s Finali…

On December 1, Eric Wallien of Roberta’s Inc. in Waldron, IN, officially purchased C. Raker & Sons in Litchfield, MI. The new identity of the company is now Raker-Roberta’s Young Plants, according to a Dec. 1 letter to Raker’s customers, suppliers, and business partners from Vice President Susie Raker-Zimmerman. “There have been minimal changes in management and we will be providing the same products and services on which we have built our reputation in the industry,” Raker-Zimmerman said in the letter, which also announced the name change and new logo. The sale of C. Raker & Sons was announced in September . A series of events affecting Raker’s financial situation caused the need for the operation to find an alternate solution. Roberta’s had been a customer of Raker’s since 2011, and the fourth generation, family owned grower-retailer was a fan of Raker’s commitment to quality. The agreement to purchase C. […]

Read More
Biocontrols in a Greenhouse

November 27, 2017

4 Opportunities to Educate Yourself on IPM Practices in…

The Michigan State University Extension floriculture team has developed four greenhouse integrated pest management sessions that will be presented at the 2017 Michigan Greenhouse Growers Expo in Grand Rapids, MI.

Read More
Parasitized aphid mummies, ladybird beetle larvae

November 11, 2017

OHP Announces Two New Ornamental Pest Management Tools

OHP recently added two new crop protection tools to its profile of biosolutions: a biological insecticide, and an ornamental fungicide.

Read More
OHP Biosolutions

September 26, 2017

OHP Acquired by AMVAC, But Will Continue to Operate As …

AMVAC has acquired OHP and its chemical and biological crop protection solutions for the greenhouse and nursery markets. The deal will close in early October, and there will be no changes to staff, products, or operations.

Read More
Hydroponics Michigan State Web

September 14, 2017

Hydroponic and Aquaponics Growers Face Possible Loss of…

The National Organic Standards Board is considering recommending that USDA revoke the ability for hydroponic, aquaponic, aeroponic, and other container-based growing methods to be certified organic, according to an update from growers at Upstart University.

Read More
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Green…

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Yellow Stick Card for thrips

July 5, 2017

Tips From a Top 100 Grower for Effective Thrips Control

A combination of conventional materials and biologicals can help provide season-long management of thrips in hanging baskets.

Read More
Primula acaulis, Botrytis, Disease, Griffin Greenhouse Supplies

May 30, 2017

BioWorks Launches New Biofungicide for Botrytis Control

BotryStop was developed for the control of pathogens such as Botrytis, Sclerotinia, and Monilinia in several crops, including ornamentals.

Read More
Adult Aphidoletes in web - Feature

May 27, 2017

How to Overcome Biocontrol Challenges by Thinking Outsi…

With a little creative thinking and adjustments to your strategy, you can overcome your greenhouse biocontrol challenges.

Read More
Cannabis Seedling

May 20, 2017

Biocontrols: A Practical Option for Cannabis

With limited options for chemical pest control, cannabis growers are incorporating biocontrols into their integrated pest management programs. More education will cement this solution as a viable option in this emerging market.

Read More
Christmas Cactus

May 18, 2017

How to Increase Branching and Flower Bud Production of …

Based on research completed at North Carolina State University, here are some methods for increasing branching and flower bud production of Christmas Cactus (Schlumbergera bridgessii).

Read More
Herbicide Drift in the Greenhouse

May 15, 2017

How to Identify and Mitigate Herbicide Contamination in…

Herbicides applied off-site or within the greenhouse can significantly damage ornamental and edible crops. Beth Scheckelhoff, an Extension Educator for Greenhouse Systems at The Ohio State University, provides some examples and basic recommendations for mitigating and preventing herbicide contamination and injury in the future.

Read More

May 4, 2017

Bayer Altus Update: Neonic Insect Control Alternative N…

Altus, a butenolide class insecticide with the active ingredient flupyradifurone, will be available beginning May 1, and is labeled for greenhouse and nursery use on ornamental plants, vegetable transplants, and indoor vegetable production.

Read More