Needing finished hardy perennials for early spring sales? It may be too late this year, but it’s the perfect time to plan for next year.
Potting up perennial liners such as phlox, hosta and astilbe in late summer or early fall to bulk up over winter is a good way to produce material for early spring sales.
But don’t forget about the other perennial favorite, ornamental grasses. Calamagrostis, Festuca, Miscanthus, Panicum and Pennisetum are a few that do well after a late summer or early fall potting.
The basics: How to get started
Plan your potting to allow enough time to root out prior to going dormant for the winter, about three to four months. This will vary by location, but generally a July to August timeframe will finish grasses in time for overwintering.
Be mindful of getting day-length sensitive grasses such as Panicum potted up too early, as they will start to go dormant as days shorten regardless of temperature. Take note, tender grasses such as Rubrum and the Napier grasses are not good candidates for bulking and overwintering.
Culture tips & avoiding pitfalls
Plant liners into gallon pots, one plant per pot, using a well-drained soil. Incorporate a three- to four-month slow release fertilizer at a nitrogen rate of 1 to 2 pounds per yard of media. Be careful not to use a longer slow release fertilizer that will keep releasing after the plants go dormant. Alternatively, you can use a standard liquid feed schedule and cut it off as plants head into dormancy.
A preventive broad spectrum fungicide drench as plants start to go dormant can help with root issues while overwintering.
Rooted pots can be allowed to go dormant outside and give winter protection alongside other perennials. This could range from being fully covered with winter cloth in colder climates to just placing plants pot to pot in milder climates.
Plants can also be overwintered in cold frames. Be careful to avoid freeze thaw cycles that can happen when they heat up during the day and freeze at night. This can be done by making sure cold frames are opened on warm days.
Coming out of dormancy
Crops can be allowed to come out of dormancy outside or brought inside a few weeks before expected sales to help break dormancy. If needed, rotate plants in alongside newly potted material.
Warm weather grasses such as Miscanthus and Panicum will respond well to 60°F nights and warmer days to help them get moving. Cool weather grasses such as Festuca and Calamagrostis will not require as much heat and can be allowed to break dormancy outside in most cases.
If grasses lack vigor, a supplemental fertilizer application after they break dormancy can help, and if they appear a little yellow, add some iron to your fertilizer application.