Don’t FALL Behind

Paul Pilon

Fall has arrived. Although it may not be the busiest season for sales, there are several considerations to properly prepare perennials for winter and give yourself the best start possible next spring. Let’s go through some of these items that can keep you from “falling” behind.

Fall cut-off dates: Depending on your geographic location, most of the perennials that are intended to be overwintered should already planted. To take advantage of Mother Nature’s conditions, and not have to heat crops in the fall while getting them established, I find it beneficial to implement fall cut-off dates for planting.

In northern parts of the country, I find the first of September to be a good time to complete the fall potting. This allows enough time for rooting and bulking prior to the plants going dormant for the winter. Locations in the middle of the country can have later cut-off dates (perhaps mid-September); whereas, southern locations can have cut-off dates as late as early to mid-October.

Bulking: One of the reasons I strictly adhere to a fall cut-off date is to ensure there’s enough time to develop a good root system before the plants go dormant. The reality is that we’re not overwintering the top growth of the plant—rather, successful overwintering entails ensuring the survival of the root system. If the roots are weak, it’s increasingly difficult to successfully overwinter a perennial. With some perennials, bulking is used to size up a plant or to overcome juvenility, allowing them to flower and appear full next spring.

If your goal is to increase plant size, keep the plants adequately moist—don’t allow them to become overly dry. As long as they’re actively growing, keep the fertility levels up, maintaining an EC between 0.8 and 1.2 mS/cm using the 2:1 extraction method. Don’t forget to provide sufficient temperatures—between 60 and 70F (15.5 to 21.1C) to optimize growth during the fall.

PGRs: In most instances, it’s not necessary to use PGRs in the fall—this is especially true for perennials whose top growth dies back completely during dormancy. It can be beneficial to apply PGRs to evergreen perennials such as Phlox subulata to manage plant size in the fall. Toning certain perennials in the fall can be a useful strategy to reduce the size of the plants next spring.

With fall applications, I’m aiming to provide an adequate amount of control without having excessive or persistent control when growth resumes next year. For this reason, I avoid drench applications, which can persist, and lean more on spray applications using conservative, but effective, rates. For fall applications, I’m generally comfortable using the same PGRs and rates I would use on these plants in the spring, but am less aggressive with the number of applications applied.

Fertility: A good practice is to provide about 50% less nutrition than you would during the growing season. See fertility comments above if you’re intentionally bulking perennials. Once the perennials go dormant, it’s not usually necessary to fertilize them.

Irrigation: During the growth phase, continue to water the plants as needed. However, as the temperatures decrease and the plants are becoming acclimated, it’s beneficial to decrease the moisture levels slightly. A small amount of water stress during acclimation is beneficial and helps perennials to become dormant faster, and improves their ability to withstand cold temperatures. However, avoid overly dry conditions.

Pests & diseases: Insects and diseases often survive the winter and catch growers by surprise when growth resumes in the spring. Future problems can be lessened or negated altogether if growers continue to scout and manage these issues in the fall.

Fall fungicide drenches: Since the goal of overwintering is to ensure the survival of the root system, applying fungicide drenches in the fall can be a good strategy. However, not all plants need this application. Plants with little or unhealthy roots would benefit more than plants that are well rooted and have healthy root systems.

Fungicides are most beneficial when they’re applied during the growth phase rather than at the onset of cold temperatures. This early application allows the fungicide to control the soil diseases and allows time for the plants to rebuild their damaged root systems. I recommend growers use a broad-spectrum fungicide or combination of products that targets the four major root/crown rot pathogens: Fusarium, Phytopthora, Pythium and Rhizoctonia.

Light intensity: It’s best to acclimate perennials at ambient or natural light intensities. Plants grown under shade will acclimate slower than those grown at high light intensities. Remove shade cloths above crops when preparing them for winter. Shade perennials won’t become injured and will benefit from the higher light levels.

Trimming: I prefer to trim perennials as late in the fall as possible. This allows them as much opportunity as possible to store carbohydrates in their crowns and roots for their winter slumber. Perhaps a good rule of thumb would be to wait until after the first hard frost to begin fall trimming.

Several growers let the plants go dormant and don’t begin trimming and cleaning until the plants have turned yellow or even brown. This approach is often used by those overwintering inside structures and allows them to clean up the plants with their limited labor force during the winter months.

For most perennials, I prefer to trim them back to about 2 to 3 in. above the top of the containers they’re being grown in. With evergreen perennials, avoid cutting them too low or avoid trimming them altogether. GT

Paul Pilon is a Perennial Production Consultant and editor-at-large of the Perennial Pulse e-newsletter. Feel free to contact him with article topics or to address your perennial production challenges. He can be reached at