Slowing Down Annuals

This week we’re sharing some tips and trick for slowing down crops that just might come in handy the next couple of weeks as you prepare for the Mother’s Day rush.

PROBLEM: The last few weeks before Mother’s Day tend to present a host of challenges for finished growers—and this year looks to be no exception. Next to pest outbreaks, one of the biggest hurdles that bedding plant producers face as crops approach the proverbial finish line is: sudden spikes in growth.

NICK’S TIP: A sudden increase in temperature like we’ve seen recently in North America is often one of the toughest factors to account for—spurring plants to suddenly “jump.” Keep the following strategies at the ready to check growth safely and with minimal impact to flowering if your annuals start to get out of hand over the next week or two.

Pinch & Trim Minimally

With roughly two weeks left before one of the biggest weekends in bedding plant sales each year, there is a limit to how much you can pinch and trim crops. Overgrown plants that need a major haircut generally take 4 to 5 weeks to appropriately flush new growth and reset color, so be strategic with removal of leggy, gangly growth.

• “Pinch to shape” on crops like hanging baskets (HBs) rather than cutting them back hard. Removal of about 1 to 2 inches from shoot tips to tighten the shape of HBs can make a major difference aesthetically without setting the crop back too far.
• Trace shoots that you plan to remove first before you cut. For example, if you have a combo pot/HB where one variety has started to overtake the others and a more serious trim is needed, start by manipulating primary shoots. Look to see which axillary shoots move with the primary shoot and picture how the plant will look with all that growth removed before you cut.
• Depending on how the plant has developed, it may be more impactful to the plant's overall shape and size to remove a more basal shoot rather than one higher on the plant.
• Most plants look a bit homely after a hard trim, particularly crops with strong basal branching habits and/or terminal inflorescences. If possible, find ways to repurpose beefy material now, rather than cutting back too hard and throwing them away in a few weeks when they don’t sell.

For example, angelonia that are too tall and starting to get a bit floppy in 4 in. pots tend to get passed over on retail benches. However, you could use them as the center “thriller” component in a mixed-species patio pot and give them the physical support they need by ensconcing them with other plant material.

If assembled with other components today, a combo like this might not be picture-perfect by Mother’s Day, but the pot would be fairly full and have enough color to entice many retail customers. While it may be a bit of a gamble, combos made from plants that likely wouldn’t sell on their own can be an effective way to reduce shrink—if done well.

Manage Moisture & Mineral Nutrients

Withholding moisture and fertilizer are key strategies to reduce runaway crop growth in the last few weeks before plants hit retail. However, drying plants down to a wilt or completely cutting feed completely can permanently affect aesthetics, so this needs to be done cautiously.

On the 1 to 5 moisture scale (1=air dry; 5=saturated), allow plants to dry down to a level 2 before irrigating again. Do not let plants reach level 1 and wilt, or foliage may become damaged and buds/flowers will likely drop.

• If it’s rainy and humidity in the greenhouse is high, you can push the dry-down limit a bit further with less risk of adverse effects. Take advantage of weather like this and hold off on watering as long as you can to keep turgor (internal water pressure in plants) low. This will help to discourage stretch that will undoubtedly occur if plants are heavily watered when humidity is high.
• Even if plants are close to (or at) finished spec and you need to slow growth, they still need mineral nutrients. With at least 2 weeks left before ship/retail, a switch to only clear water now may cause plants to develop mild mineral nutrient deficiency symptoms.
• If you normally feed at about 250 ppm nitrogen (N), simply reduce your fertilizer rate to around 125 ppm N. This will help to ensure plants still receive some nutrition, foliage retains a nice green color, and symptoms like interveinal chlorosis do not appear.
• Use of an incomplete fertilizer that lacks N but still provides other macro- and micronutrients is a great way to keep plants looking pristine while checking unwanted late-stage growth.

Plant Growth Regulators (PGRs)

One of the biggest concerns with late PGR applications is the potential impact on flowering. Whether the concern is delay, smaller flowers or bud abortion, there are a few BMPs to using PGRs late in the game on flowering annuals.

• Ethephon (ex. Florel, Collate) should never be used unless your goal is to completely reset the flowering clock and push time to finish WAY back.
• In general, avoid use of ancymidol (ex. A-Rest, Abide), daminozide (ex. B-Nine, Dazide), and uniconazole (ex. Sumagic, Concise) late in the crop cycle. These active ingredients tend to have a greater impact on flowering delay or overly strong growth restriction.
• If you have at least 3 to 4 weeks before a crop is retail-ready but plants are not quite in color, about 2 to 3 ppm substrate drenches of paclobutrazol (ex. Bonzi, Piccolo, Paclo) or flurprimidol (TopFlor) can be coupled strategically with water and mineral nutrient restriction to slow vegetative growth. Media drench applications at these concentrations achieve a nice, whole-plant effect and can be applied again if necessary. Observe the crop for at least 5 days before making the decision to apply more PGR.
• If plants are at finished spec and in color, you can ratchet up the PGR drench concentration to around 5 to 7 ppm (or higher for Southern growers, if necessary). Again, stick to paclobutrazol or flurprimidol, and plants will hold nicely but still have ample blooms in the coming weeks.