Ask the Master Gardener: Reinvigorating your roses
Don’t panic yet if you find black stems on rose bushes. Just cut them back and lightly fertilize as soon as the leaf buds start to open.
Dear Master Gardener: My roses have a lot of black stems this spring. Will they survive?
Answer: It depends. We didn’t have deep snow cover this winter and snow is an excellent insulator, so if you didn’t mulch well last fall, there could be trouble. However, if you have shrub roses that are hardy to Zone 3, or maybe Zone 4, you can cut the stems all the way back to the ground and they should regrow from the roots, true to the variety you planted. If your roses are grafted, as most floribunda or tea roses are, cut off the black part and watch for new stems to grow above the graft. If new shoots appear below the graft, they are probably from the tougher root stock and won’t produce the rose cultivar you expect. Don’t panic yet — it’s still early — but go ahead and cut off everything that is black. Give all your roses a light dose of fertilizer as soon as the leaf buds start to open.
Answer: Yes. The best time is in the fall, but early spring is the second-best time. The goal is to get a root system established before the heat of summer. Bare root trees do really well this time of year, and are usually significantly cheaper. They are easy to transport, you don’t need as big a hole, and they establish quickly. The downside is, they have to be planted as soon as possible after buying them — don’t let the roots dry out. If you buy container grown trees, knock off any soil above the flare, the first root. Make sure this flare root is planted at, or slightly above, grade so that the roots don’t start girdling and ultimately strangling the tree. Another way to prevent girdling is to box cut the root ball — use a knife or sharp spade to slice straight down the sides of the roots. Do not do any pruning of the branches — that will cause more growth in the crown and the first year you need all the energy to be growing roots. Most trees don’t need to be staked, but if you do, make sure it’s loose so the tree can sway in the wind, which tells the roots they need to keep growing. If you plant a balled and burlapped tree (B&B), remove all ties, as much burlap as you can, and after placing it in the hole, cut off the wire basket as far down as you can reach. Research shows these things don’t disintegrate over time and thus impede root growth which will lead to the tree dying prematurely. Plant the tree in whatever soil you dig out of the hole, don’t add amendments like manure, compost, or better soil. These things can be added on top which will add their nutrients gradually. Make a nice donut of mulch, 3-4 inches deep and 3-4 inches away from the trunk. No Mulch Volcanoes! Mulch piled up against the trunk keeps the trunk moist and is an invitation for disease and insects. Provide plenty of water the first year, right up until the ground freezes next November/December. For more in-depth info on tree-planting, sign up for Jackie’s free Zoom presentation on Trees: Choose Wisely and Plant Properly, next Tuesday at noon through the Brainerd Library. To register, go to krls.org or https://bit.ly/3uAgRfk .
Answer: The plant you have in your home is most likely the tropical hibiscus, Hibiscus rosa sinensis. You may put your plant outside during the summer in a sunny location, but because it is a tropical plant, you will have to bring it back in before it gets too cold in the fall if you want to keep it. A tropical hibiscus growing in a pot needs regular fertilizing every two to three weeks during the growing season.
There is a cold-hardy hibiscus, also known as “rose mallow” that you may find in garden centers. These beautiful perennials are reliably hardy to Zone 4 and need to be mulched for winter protection. Gardeners up here have been successful growing some Zone 4 perennials, due to micro-climates within their yards or heavy mulching in the fall for winter protection. Unlike the tropical hibiscus, the hardy hibiscus does not bloom continuously all summer. It does have a long blooming season, which goes from mid-summer until frost. There are some spectacular cultivars with show-stopping, huge flowers in shades of pink, red, white, and lavender. The cultivar Kopper King has 6-inch pale pink blooms with bronze foliage. Like its tropical cousin, the flower on the hardy hibiscus only lasts one day but new buds keep opening. These perennials perform best in full sun and prefer a slightly acidic soil with plenty of organic material. The hardy hibiscus does well in moist or dry conditions. In fact, they are a good choice for rain gardens, due to their tolerance of wet soils. The beautiful hardy hibiscus is relatively pest-free and disease resistant so it may be a perennial worth trying in your garden if you are willing to give it some winter protection in the fall. Keep in mind - the hardy hibiscus shows up very late, so don’t worry if you don’t see it until late May or June.
Answer: Forsythia, native to Korea and China, is a fast-growing shrub that, when grown in full sun, is covered with yellow blossoms in April. One limitation to growing forsythia in Minnesota is flower bud hardiness. However, there are two varieties that are hardy to zone 3b — Northern Gold and Meadowlark. Northern Gold reaches 8 feet tall and 7 feet wide at maturity. Meadowlark’s mature size is 10 feet by 10 feet. If grown in partial shade, it will be smaller and have fewer blooms. Forsythia is not fussy about soil, likes regular watering, and has no serious pests or diseases. It does benefit from annual pruning. That pruning should be done right after flowering is finished. Each year cut one-third of the trunks to the ground, which will stimulate new young shoots to form and will help keep the plant smaller. Unsightly and straggling branches should be removed, but the natural arching form of the plant is its most beautiful. If you have the room for it, a hedge or background row of forsythia can be spectacular.
You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at email@example.com and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.