Perfecting Perennial Production

Features - Production

Through good understanding of variety selection, learn to streamline production

August 3, 2011

Delphinium grandiflorum ‘Summer Morning’Producing perennials is generally more challenging than growing annuals. Perennial growers deal with more diverse flower initiation mechanisms than annual growers. Perennial growers often need to understand vernalization and juvenility effects to successfully bring a crop into bloom.

Through good understanding of variety selection and by following some basic guidelines, perennial growers can streamline their production practices and improve success. In addition, growers may improve production efficiency and profit margins in the process.

Plan early and set goals
Early planning is one of the most helpful things perennial growers can do to improve success. Order starter plant material at least six months before plants are needed to help ensure plants are available on the delivery date. For material produced from tissue culture propagules, ordering 12 months or more ahead may be required to ensure orders are filled, due to the long lead time for these starter plants.

Base your production schedules on the goals of your perennial program, including container sizes, targeted sales window(s) and whether plants will be sold in bloom. Knowing price points is very helpful in determining the number, type and size of starter plants and affects variety choice. For a bargain, non-flowering quart program, seed varieties may be the most suitable. While a flowering, premium quart program could include more expensive vegetative varieties.

Choose the right starter material
There are a wide range of options for starter material, from small, seeded plugs (i.e. 288-cell plugs); medium-sized 72-cell vegetative liners produced from cuttings or tissue culture; large liners (often vernalized) in 21- to 50-cell trays; and field-grown bare root divisions. The best choice for starter material depends in part on finished container size. The selling price for the container is another important factor, as this affects the upper limit of starter material cost.

Small containers, like 4-inch pots or flats, are ideal for small, economical seeded plugs such as 288- or 388-cell plugs. Some propagators produce high density vegetative liners in small trays, such as 200- or 162-cell trays. These liners are well-suited for small containers.

For medium-sized containers, such as 6-inch pots or quarts, a 128 plug is a versatile option. Small vegetative liners or 72-cell liners are also suitable. Smaller plugs can also work, as long as growers are confident in their production practices and can ensure ideal moisture management for the first few weeks after transplant.

One gallon or larger containers are ideal for large transplants, including bare root divisions and 21-, 32-, or 50-cell trays. Another option to consider is using multiple medium-sized plugs per container, to ensure good pot fill.

Some growers transplant small plugs and liners into large cell plug trays, establishing plants in these trays before transplanting to large containers. This can be an excellent option and an economical way to produce vernalized liners, as well. Generally, it takes four to eight weeks for small plugs to fill out large cell trays, depending on plant species, growing temperature and size of transplanted plugs.

Don’t assume that the least expensive option is always the best choice. Growers transplanting small plugs into medium- to large-sized containers should recognize that the first few weeks of care are critical for good establishment of small starter plants.

Poor cultural practices, especially over- or under-watering, can result in significant plant loss and eroded margins. Large plugs and liners finish faster than small plugs, which may be helpful for late season second turns.

Choosing a supplier
Ideally, the plugs and liners a grower purchases (or produces in-house) should be healthy, well-rooted, uniform and shipped in the quantities expected in the requested ship week. When comparing prices among suppliers, consider all costs, including royalties, required plant tags and shipping/boxing/handling costs, as suppliers often vary considerably in how such costs are invoiced.

Some growers choose the cheapest supplier as a cost saving strategy. Inexpensive starter material is not a true bargain if quality and consistency are sacrificed to achieve a low price, as plant loss after transplant can be significantly increased when using marginal quality plugs and liners.

Low-cost suppliers may be more likely to short ship orders, as well. This can result in growers experiencing a last-minute scramble for replacement starter material. When dealing with a new supplier with unproven quality, it can be wise to split orders, to allow for a comparison between a new and a preferred supplier.

By keeping good records about quality and performance after transplant by supplier, growers can determine how much shrink they experience. This information should be considered when planning future purchases.

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Inspecting plants

It is important to inspect all shipments of plugs, liners and other plant material received to ensure that quality is acceptable and there are no obvious signs of insects or disease organisms. Communicate any concerns to your broker or supplier immediately. If a digital camera is available, taking photographs to support your claims can be very helpful.

Pay special attention to the presence of insects such as whitefly, aphid, spider mite and thrips, as these pests can quickly build up large populations if untreated. A good quality hand lens is helpful in examining plants for these pests.

If corrective measures are needed, consider treating the plant material before it is transplanted, to minimize the amount of chemical needed and to reduce time for application. For severely infested plant material, the best option may be discarding the shipment and filing a claim.

Pre-transplant care
An excellent strategy before transplanting plugs and liners is to feed them in their trays with a liquid fertilizer solution to help ensure strong early growth. A solution of 200-400 parts per million nitrogen is ideal. Even if a slow-release fertilizer is used in containers, the pre-transplant feeding is worthwhile.

Holding plants in trays can help growers spread out transplant labor. However, perennials ideally should not be held in trays longer than a week or two to prevent degradation in quality. Ensure that held trays are watered and fertilized adequately.

High-density trays with small plants are more challenging to care for than larger plants in lower-density trays. Under warm, sunny conditions, high-density trays may need watering more than once a day. A shaded area can be used to help minimize problems with drying out.

Flower initiation
Vernalization is the process of taking perennial plants through a cooling period. The length of the cooling period, the cooling temperature and the maturity of the plant at the time of cooling are all critical factors for success in vernalization. In general, 35°F-38°F for eight to 10 weeks is usually sufficient to vernalize mature plants. The larger a plant, the less likely it is to be juvenile.

Perennial growers should understand the flowering requirements of the varieties they grow, as even within a species different cultivars can have different requirements. Varieties that flower the first year, without need for vernalization, are excellent options for growers looking to reduce overall crop time. By growing first year flowering cultivars, growers can eliminate the need for overwintering or using vernalized starter material to ensure good flowering.

Photoperiod is typically the trigger for first year flowering varieties, and long days often trigger flowering. A “long” day is typically 14 or more hours long, and can be provided artificially with night break lighting techniques. For night break lighting, 5-10 footcandles of light is provided for four hours in the middle of the night, usually from 10 p.m.-2 a.m. Incandescent light is acceptable for night break lighting to trigger flowering of long day plants.

Record keeping
Keeping good production records allows growers to more easily review each season, identifying opportunities to improve production further. By tweaking each season’s program, growers can capitalize on their successes, creating their own custom schedule for their production.

Keeping track of transplant date, plug and liner sizes, cultural practices, success at hitting sales windows, shrink, and pest control issues provides important data growers can use to fine tune their planning and production for upcoming seasons. 

Allen R. Pyle is perennial guru, C. Raker and Sons Inc., (517) 542-231; He also oversees trialing for both Raker and the Hort Couture marketing programs.