Luxurious azalea shrubs blooming in spring are increasingly common in gardens. These woody shrubs from the heather family make an elegant addition to a private home. However, many flower lovers lack experience growing this exotic plant and have no idea how to properly cover rhododendrons for the winter.
Need for shelter
Heather-like Eucaricotae are demanding plants, so in addition to creating optimal growing conditions, they require proper winter protection. Otherwise, the rhododendron's root system, located close to the soil surface, will partially or completely freeze. Partially frozen roots will subsequently cause disease and the shedding of newly formed buds.
The genus Heather comprises more than five hundred subspecies of evergreen, deciduous and semi-deciduous tree-like shrubs. Many frost-resistant species They naturally grow in northern regions and don't require shelter. However, most modern varieties and hybrids cannot withstand temperatures as low as -20 degrees Celsius and die. Therefore, many flower lovers are concerned about whether rhododendrons need to be covered for the winter.
Shelter periods
Gardeners new to growing this crop are interested in the subzero temperatures at which they should cover their plants. Almost all varieties and hybrids tolerate frosts from -8 to -12 degrees Celsius. However, if temperatures consistently reach -12 to -15 degrees Celsius, it's important to immediately ensure the plants' root systems are securely covered. This is especially true for young seedlings less than three years old.
If temperatures fluctuate, either rising or falling, it's best to postpone covering the plants. Prematurely covering the flower buds formed in the fall can lead to their rotting. Also, prolonged exposure to covering material at temperatures above -5°C (-5°F) can lead to mold at the root collar.
The established timeframe for covering rhododendrons, depending on the region, begins at the end of October and ends in mid-December.
In the Moscow region
Shelter Rhododendrons for the winter in the Moscow region Gardeners work when temperatures remain stable at -8 to -12 degrees Celsius. To ensure lush flowering in May, the shrub should be covered starting in mid-November. The most reliable shelter for young seedlings is an air-dry shelter, using heat-retaining and waterproof materials. Such shelters will prevent both freezing and damping off of the root system and flower buds.
In the middle zone
Experienced gardeners note that the timing of covering rhododendrons directly depends on the condition and age of the shrub. Typically, in temperate climates, this procedure is carried out from late October to early December. There's no need to rush to cover ornamental plants in temperate climates, as the first autumn frosts are beneficial for garden azaleas. They stimulate chemical and biological processes that boost the plants' immunity. The key is to insulate the shrubs before the air temperature drops below -15°C.
In the Urals
Garden azaleas easily tolerate light autumn frosts in the Ural region, making the plant more resilient. However, starting in late October, rhododendrons should be covered for the winter. This procedure should be carried out when nighttime temperatures drop to -12°C.
In Siberia
Rhododendrons in this region should be prepared from the first frost. To prevent young bushes from freezing, cover the plants from the last week of September until early November. When insulating the shrubs, ensure that the protective material will not only protect against frost damage but also prevent the flower buds and root collars from rotting.
In the Leningrad region
Take special care of young hybrid rhododendron bushes, which are susceptible to severe frosts. The St. Petersburg region is prone to early and sharp cold snaps, so even the most frost-hardy first-year seedlings can suffer from low temperatures if not covered in time.
The plant's shallow root system is most vulnerable, so it will require warm and substantial cover. When the ground freezes to -5 degrees Celsius, the root collar of a young rhododendron is at risk of freezing, putting the entire plant at risk. In the Leningrad Region, it's necessary to insulate shrubs starting in mid-September.
Preparing the plant
The timing of covering shrubs depends on the characteristics of the variety or hybrid. Before covering rhododendrons for the winter, it's worth taking several preparatory steps to help these dicotyledonous eukaryotes survive the cold.
Top dressing
The plant needs to replenish its mineral reserves even at the end of the season. The process of ontogenesis of the rhododendron's embryonic shoot begins from mid-August to the end of September. For the shrub to delight with lush blooms in the spring after winter, the elements essential for growth and photosynthesis must be present in the root zone before temperatures drop significantly. Only after absorbing all the nutrients necessary for growth in the fall does the plant enter a dormant phase, slowing down its metabolic processes.
To ensure all the processes necessary for entering the dormant phase are completed on time, fall fertilizers should not contain nitrogen compounds that stimulate plant growth. In late fall, when frosts approach, granular fertilizers can be applied to the root zone of the bush:
- superphosphate – 25 g;
- potassium sulfate – 25 g;
- urea – 15 g.
Over the course of the winter, the granular substances will gradually dissolve, and with the onset of spring warmth, they will be absorbed by the plant’s root system.
Trimming
The plant doesn't particularly need formative pruning, as it's genetically designed to grow a symmetrical bush. Therefore, before winter, garden azaleas only need to prune out diseased and damaged branches. The only reason to prune a bush is to rejuvenate it. This procedure is performed when the rhododendron loses its decorative appeal and lush blooms.
In the fall, before frost, cut the plant's shoots back 5 cm above the level of dormant buds. After pruning, dormant shoots will begin to grow within 10-12 days, and the garden azalea's ornamental appearance will be restored the following season. To prevent infection, immediately sprinkle the cut areas with wood ash or coat with brilliant green.
Treatment against diseases and pests
Rhododendrons, like all plants, are susceptible to diseases and insect pests that can cause irreparable damage. Resistance to pathogens and insect pests depends on the plant species and cultivar. For example, evergreen varieties grown in full sun are more susceptible to infections and pest attacks than those planted under the shade of trees. Weakened plants are more susceptible to disease, so rhododendrons need optimal conditions throughout the season to thrive.
Before wintering in late September or early October, it's a good idea to spray plants with growth stimulants to boost their immunity: Epin, Heteroauxin, and Zircon. Before covering with covering material, treat shrubs with Fitosporin, Maxim, Fundazin, Effect, and Previkur to prevent rot. To kill pest larvae overwintering on foliage and in the soil beneath the plant, spray with insecticides such as Aktara, Confidor Maxi, Opperkot, and Actellic before covering.
Covering materials
Each gardener should select the most effective material for insulating shrubs individually, based on the region's climatic conditions and capabilities.
You may be interested in:spruce branches
Branches of evergreen trees and shrubs are the most readily available material for covering garden azaleas. This insulated shelter is waterproof, creates an air gap, effectively traps snow, and protects against severe frosts. Furthermore, the distinctive scent of spruce branches repels rodents, making this material especially valuable for covering young bushes. Covering rhododendrons growing in sunny areas with natural material for the winter will protect the shrubs from UV burn in the spring.
Dry corn stalks
Another natural material that can be used to protect perennials from frost. However, during heavy rains, corn stalks should be covered with plastic.
Wood sawdust
Wood shavings effectively protect the plant's shallow root system from frost. However, it is not recommended to cover the shrub completely with them. It is best to sprinkle a 20-30 cm layer around the rhododendron. During heavy rainfall, cover the sawdust with plastic wrap and, before spreading it around the plant's root zone, mix it with a small amount of citric acid.
Thermal insulation flooring
Thanks to the unique properties of geosynthetics produced using the thermal bonding method, rhododendrons can be protected in northern regions. Thermal insulation materials are highly permeable to moisture, so it is recommended to stretch them under polyethylene. This "greenhouse within a greenhouse" is suitable for covering ornamental shrubs in the Leningrad Region and Siberia.
Protective structures
Designed to protect plants from the cold, these structures shield shrubs from harmful UV rays and rodents while allowing for good air circulation. These mini-greenhouses include dense agrofibre and metal arches insulated with PVC sheathing. The structures are made of alloys that resist corrosion and freezing temperatures. In this protective cover, rhododendrons are protected from freezing and receive the oxygen they need for a comfortable winter.
Proper cover
Necessary Caring for rhododendrons in autumn Preparing an ornamental plant for winter depends on the individual characteristics of the plant. Evergreen and deciduous heather-like eukaryotes differ in their frost resistance. However, both subspecies require root protection.
Evergreen
Evergreen garden azaleas don't shed their leaves in winter, curling up when frost sets in and unfurling again when spring warmth arrives. The shelter required for these species varies depending on the cultivar and hybrid. The following varieties require good insulation with spruce branches or lutrasil:
- Percy Weissman;
- Gold Tracht;
- Goldflimmer;
- Grandiflorum;
- Nova Zembla;
- Naselle;
- Exbury "Fireball";
- Golden Sunset;
- Simona.
The following varieties require light covering with spruce branches, pine needles or wood shavings:
- Berry Rose;
- Alfred;
- Bieber;
- Blue Peter;
- Blue Tit;
- Bourzault;
- Gold Dust;
- Violetta;
- Hessen;
- Irena Koster;
- Dagmar.
Deciduous
Deciduous ornamental shrubs of the heather family are easier to care for than evergreens. Popular varieties and hybrids of Canadian, yellow, Daurian, and Japanese rhododendrons can be simply insulated at the root zone with a 15-20 cm layer of pine needles, leaves, and wood shavings. However, if a deciduous garden azalea seedling is less than two or three years old, it must be covered with spruce branches or other insulating material.
Adviсe
To avoid mistakes when preparing rhododendrons for winter, follow the recommendations of experienced gardeners:
- It is generally forbidden to water rhododendrons during wintering, gradually reducing the supply of liquid from the beginning of autumn;
- Do not remove the insulating material from the shrubs once the snow has melted. This procedure should be performed after the soil has warmed and there is no longer a risk of spring temperatures dropping below freezing.
- When insulating shrubs, take care to protect flower buds and preserve apical shoots. This procedure is performed by bending the branches toward the ground. Despite their massive size, even mature shrubs tolerate this bending well.
- Check the shelters throughout the winter: brush off excess snow, promptly replace any agrofibre damaged by the wind;
- If you cover the plant too early, the root-stem transition zone will begin to rot, the foliage will become covered with mold spores, and the bush will die. To prevent rot, uncover the covered garden azalea on the sunny side. After keeping the bush uncovered for two weeks, cover it again when temperatures return to below freezing.
With proper insulation, these "pets" will survive the winter without a problem. And in the spring, they'll delight their owners with lush, vibrant flowers.
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