Ground Breaking Banter - Rick
The USDA hardiness zone system exists to help us pick plants that will survive winter in our area. But as we’ve often discussed on the show, it’s not always enough to know if that plant will actually thrive after winter. For example, flower buds may be killed off and the plant doesn’t bloom or set fruit. As such, many people take steps to protect their plants over winter using methods that range from the conventional to the cockamamie. In this episode, we talk about when you might want to protect plants – spoiler alert: it’s rare.
Join us at the YouTube link above or on your favorite podcast platform for our whole conversation on protecting plants for winter.
The best strategy when it comes to plant protection is to simply choose plants that thrive in your area without the need for protection, and site them appropriately so that if a bit of protection is beneficial, they will get it naturally rather than you having to provide additional protection. But sometimes, it’s not always clear whether protection is needed. After all, as we’ve discussed on the show many times, the hardiness zone system only addresses the maximum cold temperature a plant is believed to withstand and survive; it doesn’t address how badly it might be set back, whether any flower buds on the plant over winter will be damaged, etc. And one area where that really, really matters is broadleaf evergreens.
This is a term that people like us throw around a lot without any explanation, and if you do take a moment to think about it, you’ll figure it out. A broadleaf evergreen is an evergreen shrub or tree that is not a conifer. So instead of having the needle like or scale like leaves associated with conifers, it has wide, or broad, leaves, that stay on the plant all winter. Some familiar broadleaf evergreens include rhododendron, blue holly, boxwood, and gardenia. The warmer your climate, the more broadleaf evergreen options you’ll find available to you, though a number of them are hardy, or hardy-ish, like today’s plant on trial, Sky Box Japanese holly (Ilex crenata).
If you aren’t familiar with it, to the casual observer, Japanese holly appears almost identical to boxwood. Both are broadleaf evergreens with small leaves, insignificant flowers, and come in a variety of shapes and sizes that are perfect for hedges and specimen plantings. They are very simple to tell apart, though: the foliage on boxwood is opposite, and the foliage on Japanese holly is alternate. And another key difference is that, by and large, boxwood tends to be hardier than Japanese holly, and this may be why you haven’t heard of it.
That is, hardier with one major exception: the narrow, upright selections of boxwood tend to be the least hardy, often to USDA zone 6b or even 7, whereas there are many upright narrow forms of Japanese holly that can be grown in USDA zone 5 with protection – like today’s plant on trial, Sky Box Japanese holly.
Sky Box naturally grows as a narrow column, reaching just 2-3’ wide and 4-5’ tall. It takes on a pyramidal shape, with a strong point at the top, and doesn’t need any trimming or pruning to keep this useful, handsome shape. It does have small white flowers in late spring, but they are largely insignificant. It can be grown in most any well-drained soil, though does prefer things on the acidic side, which is true for broadleaf evergreens as a whole.
We sell Sky Box Japanese holly as hardy to USDA zone 5, but if you are in this colder part of its range, you might consider planting it in a somewhat protected spot where it will be sheltered from the worst of the winter winds, which will cause the foliage to dry out, and so that it will experience less dieback and potentially damage its unique habit. But really, the most important measure of protection that gardeners anywhere should offer all of their plants but especially broadleaf evergreens is mulch. A good 2-3” layer of shredded bark mulch is absolutely key to keeping the plant happy through winter by conserving moisture and insulating roots. If fall is unusually dry, that may need to be coupled with some late season watering.
Sky Box Japanese holly came to us from Maryland nurseryman Mike Farrow. It is hardy to USDA zone 5 and heat tolerant through USDA zone 8. It makes an excellent specimen plant, or paired at your front door for a touch of formality, where its strong structure also lends itself beautifully to draping with lights for the holidays. It is not quite as shade tolerant or as deer resistant as boxwood.
If you’d like to add Sky Box Japanese holly – or any of the 320+ Proven Winners ColorChoice Shrubs – to your garden or landscape, you’ll find a list of local retailers here.
Gardening Mail Bag - Stacey
Firming the soil around the roots of a shrub – or any plant – that you just planted is a key part of the planting process. It removes air pockets that may interfere with root growth and helps to stabilize the new plant while it grows roots in its new home. However, it is absolutely possible to overdo it, and that is much more likely to happen if you’re using your feet instead of your hands. It’s especially crucial to be gentle in this stage if the soil is wet, and as wet or moist soils are more susceptible to compacting from traffic or overworking. Use your hands to firm the soil around the plant and make sure that the soil fills any gaps between the rootball and planting hole – which isn’t something you can get from using your feet anyway.
Chinese hibiscus is Hibiscus rosa-sinensis (which translates to “rose from China”) and is often colloquially called “tropical hibiscus.” These plants are most often bought as summer color in cold climates, and many people do attempt to bring them indoors to overwinter them in the hopes of another fabulous display the next year. However, once they come indoors, they very often lose all of their foliage. So it’s unusual that yours seems to have lost its foliage during the prime of the growing season, but that can happen if it experiences stress (especially water stress). Bring your plant indoors to the coolest, brightest spot you have. Avoid blasts of heat from a register or radiator, and similarly, avoid blasts of cold from doorways. The soil should not remain consistently moist, but nor should it be allowed to dry out. Do not fertilize. You are likely to find that your plant will defoliate again but with some luck and TLC, it should be able to limp through winter enough that you can grow it next summer and give it a chance to recover, enjoying a full growing season to better equip it to deal with the challenging conditions indoors.
The answer to this depends on where you are located. If you are in a mild climate (say, USDA zone 8 or warmer), you probably can still plant some grass seed now and get good results. In colder areas, though, late November – even if it’s unusually mild – is unlikely to provide a long enough window for germination and rooting to get established. If you live in a cold climate and already have grass seed, go ahead and sow some in the spot you want to fill and see what happens. If you’d be buying grass seed for this project, we recommend waiting until spring.
Do you have a question for us? We’re happy to help! E-mail us or use the contact tab above. Due to high volume, we may not get to your question, so if you need an answer quickly, please reach out via the Proven Winners website.
Branching News - Rick
Amaryllis are a classic holiday plant – and popular to give as gifts as well. But over the past few years, suppliers have taken to coating them with wax to disguise the bulb and reduce maintenance needs. And Rick does not like it! He goes off on a bit of a rant in this episode of Branching News that you’re not going to want to miss.
