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...
Bees And Pesticides

August 23, 2016

Studies Offer Conflicting Views On Neonic Effect On Bee Health

How much exposure to neonicotinoids do bees need before their health becomes affected? That’s the question two research teams look to answer.

Read More
Chrysanthemum Aphid

August 22, 2016

How To ID And Manage Black Aphids In Chrysanthemums

Growers in Michigan have recently been reporting a higher presence of this pest. Here are some tips on how to control it.

Read More
Cannabis Crop Protection

August 22, 2016

Cannabis Group Stays Focused On Consistent Standards For Crop Protection

The Foundation of Cannabis Unified Standards (FOCUS), is an independent, third-party, not-for-profit organization, is in the process of developing cannabis-specific standards for everything from cultivation and extraction to packaging and retail.

Read More
Latest Stories
Bees And Pesticides

August 23, 2016

Studies Offer Conflicting Views On Neonic Effect On Bee…

How much exposure to neonicotinoids do bees need before their health becomes affected? That’s the question two research teams look to answer.

Read More
Chrysanthemum Aphid

August 22, 2016

How To ID And Manage Black Aphids In Chrysanthemums

Growers in Michigan have recently been reporting a higher presence of this pest. Here are some tips on how to control it.

Read More
Cannabis Crop Protection

August 22, 2016

Cannabis Group Stays Focused On Consistent Standards Fo…

The Foundation of Cannabis Unified Standards (FOCUS), is an independent, third-party, not-for-profit organization, is in the process of developing cannabis-specific standards for everything from cultivation and extraction to packaging and retail.

Read More
Leaf Septoria In Cannabis

August 21, 2016

Three Diseases To Watch For In Cannabis Production

The development of root rot, powdery mildew, and leaf septoria can damage cannabis to the point of complete crop loss.

Read More
Greenhouse Whitefly

August 18, 2016

Vestaron Planning For More Research And Development Of …

On the heels of launching Spear-T, its first bioinsecticide, Vestaron has received additional financing that will be used to develop new products with new modes of action.

Read More
BioWorks Mycotrol

August 17, 2016

New Organic Mycoinsecticide From BioWorks Now Registere…

BioWorks’ Mycotrol can be used to manage whitefly, thrips, aphids, and other insects in greenhouses and nurseries.

Read More
Downy mildew lesions on light coleus cultivars feature

August 12, 2016

How You Can Control Downy Mildew In Coleus, Roses, And …

Downy mildew diseases are potentially devastating to ornamental crops and at the very least can cause unsightly damage. Check out the latest research and recommendations for preventing it.

Read More
Jen Browning BASF

August 4, 2016

Horticulturist And Entomologist Jen Browning To Speak A…

Browning will discuss the use of nematodes in managing pests in greenhouses and nurseries.

Read More
Poinsettia, Heavy Whitefly Infestation -Lower Leaves, Insect - Feature

August 3, 2016

Tips For Successful Late-Season Whitefly Control

Managing late-season whiteflies successfully on poinsettia requires preventative measures put in to action early in the production cycle.

Read More
Cannabis Crop Protection

July 28, 2016

Solving The Cannabis Crop Protection Problem

A largely unregulated sector of the industry, state departments of agriculture, biocontrols companies, and other industry pros are dedicated to helping growers make the right pesticide decisions for their operations.

Read More
Aphids On Older Leaves

July 25, 2016

How You Can Stop Aphids By Understanding Their Interact…

Knowing which aphids target which crops and how aphids colonize and move on plants goes a long way toward setting up an effective management plan.

Read More
BASF Orkestra Intrinsic

June 21, 2016

New Mode Of Action From BASF Offers Deeper Disease Cont…

When it comes to disease control, you need all the help you can get. BASF recently hosted growers, Extension personnel, and trade media to present its newest fungicide with two active ingredients, offering dual modes of action.

Read More
Nematodes-feature

June 4, 2016

New Biocontrols Provide Effective Pest Control In Green…

Biological chemistry manufacturers have introduced several new products recently that offer a range of insect and disease management options. Here’s a look at some of them.

Read More
Whitefly

June 2, 2016

Breaking News: Florida Growers Reporting Major Whitefly…

Reports have come from the Florida Keys to Palm Beach County that whitefly populations in landscapes are reaching unprecedented levels and are not responding to pesticide applications. Biotype-Q has been found in four different communities. University of Florida/Institute of Food and Agricultural Science researchers are working with USDA-APHIS, USDA-ARS, the Florida Department of Agriculture, and growers and landscape professionals to manage the developing problem.

Read More
Triathlon BA container shot

May 24, 2016

OHP’s Triathlon Biofungicide Now Listed By The Organic …

Triathlon BA is a broad-spectrum preventative biofungicide that provides control of many foliar and soilborne diseases in ornamentals and herbs.

Read More
Two-spotted spider mites, adults and eggs

May 11, 2016

SePRO Launches Summer Insecticide Management Program Fo…

The program is designed to help growers use SePRO’s insect management tools to prevent plant damage from a variety of pests.

Read More
Small Aphid Colony on Calibrachoa

May 2, 2016

How To Stop Aphids In The Greenhouse

When untreated, aphids damage ornamental crops and act as vectors for disease. Integrated Pest Management combined with vigilant scouting can help you stay ahead of the problem.

Read More
Cicada (Greg Hoover, Penn State)

April 26, 2016

Cicadas Set To Emerge In Several Eastern States This Sp…

While there’s no immediate cause for alarm, experts say the cicada’s egg-laying process can damage woody ornamentals and make them vulnerable to diseases.

Read More
[gravityform id="35" title="false" description="false"]