Controlling containerized herb growth

Departments - Hydroponic Production Primer

Because PGRs are not an option, growers need a clear strategy to successfully grow herbs in containers.

August 17, 2021

The first step in controlling containerized herb size is taken when you select the cultivars to grow.
Photo: JackF, Adobe Stock

Containerized culinary herbs are popular year-round. But as ubiquitous as they are, they present a key production challenge: controlling their growth.

Unlike fresh-cut culinary herbs grown in hydroponic systems, the size of container-grown herbs is important. First, more compact finished plants can improve space utilization, from closer spacing on the bench to increased plant densities in the greenhouse. Second, more compact herbs can improve water and nutrient use, as less is consumed by smaller plants. Finally, containerized plants are simply more attractive when they are proportional in size to the container they are grown in. These are many of the same reasons why growth of containerized flowering plants is controlled.

However, unlike floriculture crops, there are no plant growth regulators (PGRs) that can be applied to control growth. This article will focus on those factors — genetic, environmental, and cultural — which can be used to help control containerized herb growth.

The first step in controlling containerized herb size is taken when you select the cultivars to grow. In addition to flavor, foliage appearance, and a myriad of other factors, herb cultivars vary in their finished size. For containerized herb producers, selecting smaller or more compact cultivars to finish can help with meeting height targets. While compact cultivars are useful, they are not always available for each herb species. Basil, the most popular and widely grown containerized herb in North America, has a number of compact-growing cultivars that can be used for producing green-leaf sweet basil plants. Although not nearly as numerous, there are also compact dill cultivars available. However, for a number of herb species, there are no compact cultivars available to choose, and growth control will have to come by controlling the environment and culture, and not genetics. For many other species, there are such few cultivars available, and in general, these are much less compact varieties.

Controlling irrigation is one step growers can take to manage containerized herb growth.

One cultural approach to take in controlling containerized herb growth is by controlling irrigation. The more “wet” herbs are grown, not only is the tissue softer growth, but plants are larger. Conversely, by restricting irrigation and growing containerized herbs on the dry side, plants are more toned for shipping and disease pressure is reduced while excess growth is inhibited. Growing dry can be a challenge, depending on the degree of dryness desired and how plants are irrigated. Growing slightly drier is achievable for both hand-watering and automated approaches.

Pushing the crops and growing with moderately to severely restricted irrigation is not as simple. For hand-watered crops, an extremely attentive and observant approach is needed in order to catch plants before they reach the permanent wilting point, which can cause irreparable damage to plants. Automated irrigation systems incorporating soil moisture sensors can be more successful when imposing a greater degree of drought stress, as plants can be irrigated when necessary. While reducing available water will suppress growth of nearly all herbs, the magnitude of effectiveness varies among species; drought-sensitive species respond more than more drought-tolerant species.

Modifying fertilizer practices is another effective strategy for controlling containerized herb growth. First, evaluate the nitrogen concentration being applied. Using a lower concentration of nitrogen — 75 to 100 ppm N — from a complete, balanced, water-soluble fertilizer can produce healthy-looking plants and more compact growth. Culinary herbs are efficient in nutrient use, so lower fertilizer concentrations can provide sufficient mineral nutrients to keep foliage appearing deficiency-free and result in adequate growth. In addition to reducing nitrogen concentrations, try to minimize phosphorous. Phosphorous contributes to stem elongation, and the same phosphorous restriction strategy commonly used for growing seedling plugs can also be used when finishing containerized herbs. Concentrations of ~10 to 20 P2O5 (the form of phosphorous in fertilizers) are sufficient to suppress unwanted growth and avoid any deficiency symptoms such as lower-leaf purpling.

Without any plant growth regulator to apply on container-grown culinary herbs, producers have to look for other growth-controlling strategies. While none of the approaches presented in this article will result in all the control you may need, an integrated approach using several techniques can.

Christopher (ccurrey@iastate.edu) is an associate professor of horticulture in the Department of Horticulture at Iowa State University.

More than cute: Max out your greenhouse space with dwarf pepper varieties

Departments - Edible Insights

Discovering micro-pepper cultivars and their potential in greenhouse vertical growing systems.

August 17, 2021

Leslie F. Halleck

As I walked the AmericanHort Cultivate‘21 tradeshow floor this past July — my first business trip and conference in more than eighteen months — my eyes scanned the booths seeking out tiny plants with enormous potential. Tiny edible plants, specifically, that make growing produce more accessible and successful for the indoor gardener. While micro-tomato cultivars have garnered the most focus in this area — and this was certainly evident by all the new micro-tomatoes at the show — I was excited to see new offerings of miniature pepper cultivars.

What do dwarf or micro-pepper cultivars for the hobby market have to do with commercial greenhouse production? Well, real estate is real estate, right? Space is always at a premium and yield per area is what it all comes down to. A challenge for those of you growing under glass or trying to expand your CEA’s offerings, is plant size and inputs. Fruiting plants, versus small leafy greens, are simply too big for many types of indoor controlled environments, not to mention more difficult to manage in terms of lighting and other resources. Larger crops also require a lot more labor when it comes to training them vertically, as well as lighting them properly. You can stack many racks of compact lettuces and leafy greens, but tomatoes and peppers? Not so much.

Peppers in greenhouse production are typically grown vertically, with two separate stems trained into an upright habit, much like vining tomatoes. While they don’t reach the heights that vining tomatoes do, nor need to be angled as many tomatoes are, they can still have a sizable vertical profile. And you can’t really pull the brittle stems down as you grow and harvest, like you can with tomatoes.

Most growers who are growing peppers under glass are strictly growing standard bell peppers. But with the growing popularity of hot and sweet peppers of all types, shapes and colors, you might be missing out on potential profits if you stick only to bells. Could dwarf and miniature cascading types of spicy peppers offer you both diversification and space-saving solutions without sacrificing yield?

Small peppers proved to be a big hit at this year’s Cultivate’21 event in Columbus, Ohio.
PHOTO © fusolino | ADOBE STOCK

Petite pepper player

At the Cultivate‘21 show, I was particularly impressed with the Prudac booth (http://prudac.com/), which was filled to the brim with their latest micro-tomato and micro-pepper varieties. In fact, they cornered the market on new dwarf edibles, having more than any other vendor at the show. I was instantly drawn in by their unique tiny tomato series, including tabletop Heartbreaker series, Sweet Sturdy series, the itty bitty Ponchi series, and the Pillar series for micro-trellising. PanAmerican Seed also had an impressive display of their new micro-tomatoes at the show. All these tiny tomatoes are not only perfect for the home grower market, but also offer super space-saving solutions for anyone wanting to get into the tomato game in smaller controlled environments.

Prudac also brought serious mini-pepper game, offering cascading basket types and compact narrow-growing peppers for trellising, with a mixture of sweet and spicy varieties. Their Peppers from Heaven series offers plants with a lush cascading growth habit; with plant height ± 15-25 cm / 6-10” and width ± 15-30 cm / 6-12”. Red and orange cultivars are currently available. These plants could make excellent options for hanging or other types of vertical hydro production. I was also intrigued by their Ponky Pepper ‘Spicy Jane,’ which they claim stays under 15 cm / 6” but can trail or train to a width of 60 cm / 24”. Now, Prudac states on their site that Ponky Peppers aren’t yet available in North America, but hopefully that will change.

But it was their slim-growing Pillar Peppers series that really had me doing a double take. These small, narrow, but sturdy little peppers appear to offer good production with less labor and space. Pillar Peppers seem perfect for high density culture and small pots (both for commercial production and home hobby growing). A series within a series, the Pillar Pepper Galaxy series offers red, orange and yellow cultivars with a mild spicy taste, with plants growing less than 20-25 cm / 8-10” tall and wide. All the dwarf peppers I inspected at the show appeared fruit-heavy with minimal branching.

If you’re a small grower with minimal space, and you’d like to branch out from leafy greens into fruits, miniature peppers could be a suitable place to start. Given that peppers are typically easier to grow — specifically more heat- and drought-tolerant — than tomatoes (not to say peppers growing in controlled environments don’t have their common issues), they might be a safer starter crop if you aren’t already growing or experienced with tomatoes.

Growing bigger profits in the new year just might mean growing small and spicy!

Leslie (CPH) owns Halleck Horticultural, LLC, through which she provides horticultural consulting, business and marketing strategy, product development and branding, and content creation for green industry companies. lesliehalleck.com

Full coverage

Departments - Editor’s Letter

August 16, 2021

Matthew J. Grassi, Editor

Greetings, readers! You’ll find our annual State of the Industry research report for the CEA produce market issue (starting on page 16) inside this issue.

Our annual effort to uncover what’s helping and what’s hampering your operation revealed several interesting developments that occurred over the last 12 months. Here’s a small sample:

For one, I found it incredibly interesting that our survey group basically had no middle – 56% were either among the largest (100,000 sq. ft. under cover or more) or the smallest (from those less than 1,000 to those just under 2,499 sq. ft.) operations in the market. Couple that with the sales volume data – 65% either topped $1 million in annual revenue or secured somewhere between $1 to $9,000 in revenue this growing season – the picture becomes clear: in CEA produce, the big are scaling up and getting bigger, and yet smaller, localized operations are still finding opportunities.

The crops we grow under cover are evolving and shifting from year to year, as well.

Hot peppers – varieties like jalapenos, habaneros and the notoriously mouth-scorching Carolina Reaper (bred by the hilarious and equally brilliant Smokin’ Ed Currie down in the Carolinas – check out his PuckerButt Pepper Company YouTube channel) – have taken their rightful place among herbs, cucumbers, lettuce and tomatoes in the Top 5 most-grown crops under cover. It seems chefs and foodies and everyone else can’t get enough of these spicy, vibrantly colored chili plant hybrids. I must admit a bit of a bias here, as I annually produce a late-summer bounty of container-grown hot peppers for friends, family, co-workers, and even the chef at my local watering hole. It’s kind of my thing.

Conversely, you told us that managing the horticultural supply chain was a bear in 2021. We’re hoping that lessens in 2022 – but the early read we’ve gotten from talking with suppliers, breeders and growers is that unwelcome supply-side tension is probably here to stay.

OK, that’s all from me for now! Head over to page 16 and dig into the data … and if anything draws your eye, drop me a line at MGrassi@GIE.net.

Matthew Grassi, Editor | mgrassi@gie.net | 216-393-0362

Rearing parasitic wasps

Features - biocontrols

Learn the steps of an aphid banker plant system for another tool in your integrated pest management program.

July 21, 2021

Several species of aphid attack greenhouse grown vegetables, spring bedding plants and ornamentals. Some can be managed effectively with parasitic wasps using an aphid banker plant system. Banker plants are a self-contained sustainable system that supplies a non-pest prey species to support a continual source of natural enemies that disperse into the crop in search of other pests.

For the aphid banker plant system, Rhopalosiphum padi, a cereal grass pest that doesn’t attack most greenhouse plants, is raised on grain plants. Aphidius colemani is a parasite commonly used to manage several aphid pest species found in greenhouses. This parasite can be released onto the banker plant when the population of the cereal aphid is high enough to sustain the parasite population. Over time, the parasite population will increase sufficiently so that it will disperse into your crop in search of pest aphids. The banker plant will continue to produce more parasites as long as there are cereal aphids.

Most spring bedding plants and vegetables such as greenhouse-grown tomatoes and cucumbers, particularly those that are dicotyledonous plants are appropriate for this system. Do not use this system with monocotyledon plants, including Easter lilies, Alstroemeria, ornamental grasses, orchids, day lilies, iris, spring bulbs, palms, sweet corn, onions and garlic.

Aphidius colemani is the parasite that’s released on the banker plant.
Photo courtesy of UVM; Photo by Laura Sorrensen; Photo by Adam Sisson

How many banker plants do you need?

Rates can be variable based on several factors (crop, parasites/predators supported, time of year, etc.). Ask your biocontrol supplier to find which rate is the most appropriate for your operation. Biobest recommends starting out with at least two banker plants per acre of greenhouse. For operations with less than an acre, start with two banker plants. Each week after first introducing the banker plants, add one more banker plant per greenhouse or acre. For this system to work effectively, it is critical to continue to produce and add new banker plants throughout the season, until around July 1. Then you should have enough banker plants to provide management against most of your aphid pests until late August when the system is usually abandoned.

When should I start to produce banker plants?

Banker plants are used as a preventive IPM tool. They should be put into greenhouses as soon as they are opened up and production plants are added. It takes at least three to four weeks before a banker plant is producing adult parasites, so do not wait until you see the first aphid in your crop to start your banker plants.

Materials needed

An extra-large (24-inch) white polypropylene hairnet/bouffant or a dedicated aphid banker cage. Cages are available commercially or you can make your own.
Plastic plant pots or hanging baskets (12-inch diameter)
Potting soil (whatever you commonly use for your crop plants)
Grain seed: Winter barley, oats or winter wheat. Winter wheat is ideal because the grass blade is particularly wide, which supports a larger population of aphids.
Starter population of bird cherry oat aphid (Rhopalosiphum padi)
Aphidius colemani (the parasite to release on the banker plant).

Step-by-step procedure

Start aphid banker plants six weeks before you plan to start plants in a greenhouse in the spring. It takes that long to get the system up and running and ready to use in a clean greenhouse. Banker plants should be put into the greenhouse on the same day you warm up the house and start to fill it with crop plants.

Hairnets are an alternative to building or buying an aphid banker cage.

Week 1

When the aphid starter populations arrive, fill four plant pots with potting soil and make the soil moist (enough for up to two banker plants per greenhouse).
Plant one cube of the aphid starter population per pot directly into the moist potting soil.
Scatter half a cup of grain seed per pot directly on the moist potting soil around the starter.
Immediately cover each pot with a hairnet or place in containment cage. If you don’t, stray parasites can get in and destroy the cereal aphid population before it is able to build up on the grass.
Continue to water pots as needed, and lift up the edge of the hairnet, making sure you reseal the pot. Don’t over water. The greenhouse temperature should be 70-75°F.
Place an order to receive 500 A. colemani each week for three to four weeks, with the first shipment to arrive the following week.

Week 2

Fill four plant pots with potting soil and make the soil moist.
Scatter half a cup of grain seed per pot directly on the moist potting soil.
Immediately cover each pot with a hairnet or place in containment cage.
Using scissors, trim off three to five sprigs of grass blades containing a few cereal aphids from pots started week 1. Lift up the edge of the hairnet on the newly seeded pots and place these grass sprigs on the moist potting soil and grain seed. When the seeds germinate, the cereal aphids will move to the new plants. Don’t lift the hairnet until you are ready to add the infested grass so parasites don’t get into your banker plants.
Release 100 A. colemani wasp mummies evenly into each of the pots you started on week 1. If there are very few aphids on the banker plant, you may want to wait a week before introducing the parasites. Continue to water pots as needed. Do not over water. Hanging baskets can be put on a drip irrigation system.
Important note: Make sure you release the parasites after infesting week 2 pots with cereal aphids (step 4) so you don’t accidentally let parasites in those pots.

Week 3

Repeat steps 1-3 from week 2.
Follow step 4 above, taking sprigs of infested grass from week 2 pots.
Release 100 A. colemani wasp mummies into each of the pots you started on week 2, as described in step 5 above. You should see a few aphid mummies on the grass.
Continue to water pots as needed. Plants from week 3 and 4 are covered with hairnets; week 1 and 2 and are uncovered to allow parasites to disperse into the crop.

Rhopalosiphum padi (bird cherry oat aphid) is the aphid bank starter insect.

Week 4

Repeat steps 1-3 from week 2.
Follow step 4 above, taking sprigs of infested grass from week 3 pots and then infesting week 3 pots with the parasites.
Remove hairnet from week 1 pots then place the pots around the greenhouse. You should see parasites flying around the plants and aphid mummies with exit holes.
Continue to water pots as needed.

Week 5

Repeat steps 1-3 from week 2.
Follow step 4 above, taking sprigs of infested grass from week 4 pots.
By now parasites should be established and additional releases should not be needed.
Remove the hairnet from week 2 pots and place them near the week 1 pots in the greenhouses.
Continue to water pots as needed.

Week 6

Repeat steps 1-3 from week 2.
Follow step 4 above, taking sprigs of infested grass from week 5 pots to put in week 6 pots.
Remove the hairnet from plants started in week 3 and place them around the greenhouse.
Move week 1 pots to other greenhouses you are starting to fill with crop plants.
Continue to water pots as needed.

Future weeks

Continue to start new banker plants weekly until July. Before discarding old banker plants, place under a bench for 7-10 days to let remaining parasites emerge. Keep an eye out for an infestation of hyperparasites, tiny wasps that lay an egg in the A. colemani which has parasitized an aphid. Watch for a jagged and uneven parasite exit hole in the aphid mummy. Hyperparasites can wipe out your A. colemani population if allowed to reproduce. Destroy any remaining aphid banker plants at the end of the season to avoid the buildup of hyperparasites.

Margaret Skinner, Ph.D., is an extension entomologist and research professor (mskinner@uvm.edu) and Cheryl Frank Sullivan, M.S., is an IPM research technician and Ph.D. candidate (cfrank@uvm.edu) at the University of Vermont’s Entomology Research Laboratory. Ronald Valentin is the director of technical business at BioWorks (rvalentin@bioworksinc.com).