Dahlias are among the most popular ornamental garden plants, valued for their large, vibrant flower heads and long blooming period. Depending on the variety, the plants can differ considerably in height, as well as in the shape and size of their flowers. Low-growing dahlias are used for flower beds and borders, tall varieties for creating floral arrangements, while large-flowered varieties are often grown as cut flowers.
With proper care, dahlias can bloom from midsummer until the first autumn frosts. At the same time, these plants are warmth-loving, cannot tolerate frozen soil, and require regular watering and feeding.
When to plant dahlias, how to care for them, and what to do with the tubers in autumn is explained by UNN.
When and where to plant dahlias
Dahlias are planted in open ground in spring, when the threat of severe frosts has passed and the soil has warmed sufficiently. The exact timing depends on the region and the weather, but in most regions of Ukraine, favorable conditions usually occur in May. However, experienced gardeners advise taking both the calendar and air temperature into account.
Choose a sunny location protected from strong winds for dahlias. For abundant flowering, the plants need at least six hours of direct sunlight per day. In deep shade, the shoots may become elongated and the number of flowers may decrease. It is important to avoid low-lying areas and other spots where water remains for a long time after rain. Constant waterlogging is dangerous for the tubers and may cause them to rot.
Before planting, the tubers should be inspected. Severely damaged, soft, or rotten parts should be removed. Tall varieties may require support. It is more convenient to install it immediately during planting so as not to damage the root system later.
The distance between plants is determined according to the variety. Compact dahlias can be placed closer together, whereas tall, spreading bushes need more space for proper lighting and air circulation.
What soil is suitable for dahlias
Dahlias grow best in fertile, loose, well-drained soil. The soil should retain sufficient moisture while not becoming waterlogged after rain or watering.
Before planting, the soil can be enriched with well-rotted compost or other mature organic matter. Heavy clay soils require particular attention to drainage. If water regularly stagnates on the site, it is better to create a raised bed for dahlias or choose another location.
It is undesirable to use fresh manure immediately before planting. An excess of nutrients, especially nitrogen, can stimulate vigorous growth of green mass at the expense of flowering.
How to water dahlias
Dahlias require regular moisture, especially during active growth, bud formation, and flowering. The frequency depends on the temperature, amount of rainfall, soil type, and plant size.
After planting the tubers, excessive watering is undesirable until active growth begins. In cool, wet soil, tubers are particularly vulnerable to rot.
After well-developed shoots appear, water dahlias abundantly, but do not allow the soil to remain constantly waterlogged. It is better to water deeply but less frequently than to moisten only the top layer of soil every day. Water should be directed mainly at the base of the plant.
In hot, dry weather, the need for moisture increases. A layer of organic mulch will help retain it. It also suppresses weed growth and protects the root zone from sharp temperature fluctuations.
What to feed dahlias
Dahlias need balanced nutrition for active growth and prolonged flowering. If sufficient compost was incorporated into the soil when preparing the site, the plants will already receive some of the nutrients they need during the initial stage.
Later, you can use complete fertilizers for flowering plants according to the manufacturer's instructions. After bud formation begins, it is especially undesirable to overuse nitrogen fertilizers. Excessive nitrogen may cause the bush to produce abundant foliage while flowering less profusely.
The condition of the plant also says a lot. Weak growth, changes in leaf color, or poor flowering may be related not only to a lack of fertilizer, but also to improper watering, unsuitable soil, diseases, or root damage. Therefore, increasing the amount of fertilizer just in case is not advisable.
Pruning and Training Dahlias
Training helps produce a stronger bush and control its size. When a young plant has developed several pairs of true leaves, the shoot tip can be pinched out. This stimulates the development of lateral shoots and makes the bush more branched.
Tall-growing varieties must be tied to a support in a timely manner. This is especially important for plants with large flower heads: after heavy rain or strong gusts of wind, their heavy stems may break.
Throughout the season, it is recommended to regularly remove faded flowers. If they are left on the plant, the dahlia will spend resources on producing seeds. Removing spent flower heads helps maintain the bush's ornamental appearance and stimulates the formation of new buds.
Damaged, dried, or diseased leaves should also be removed, and plant debris showing signs of disease should not be left in the flower bed.
Dahlia Diseases and Pests
Among the problems gardeners may encounter when growing dahlias are fungal diseases, rots, and viral infections. The risk of fungal diseases increases with excessive moisture, overcrowded plantings, and poor air circulation.
For prevention, plants should not be planted too close together. When watering, it is advisable to avoid wetting the leaves unnecessarily, especially in the evening. Affected parts of the plant should be removed promptly.
Common dahlia pests include aphids, slugs, snails, and spider mites. Young shoots are particularly attractive to slugs and snails, so plants should be inspected regularly after the seedlings emerge.
The control method depends on the specific pest and the scale of the infestation. When there are only a few insects, mechanical removal or washing them off with water may sometimes be sufficient. If insecticides or other plant-protection products are used, it is necessary to follow the instructions and consider their possible impact on bees and other pollinating insects.
How to Prepare Dahlias for Winter
Dahlias originate from warmer climates, so their tubers are not adapted to severe ground freezing. In Ukraine, they are usually dug up in autumn and stored until the following spring.
After the first frosts, when the above-ground part of the plant turns black and dies back, the stems are cut off. The tubers are carefully dug up, taking care not to damage them with garden tools.
After digging them up, excess soil is removed, the tubers are inspected, and damaged or rotten parts are cut away. Before long-term storage, the tubers are allowed to dry.
In winter, the planting material is kept in a cool, dark place where the temperature remains above freezing. The main task is to prevent both freezing and complete drying out or rotting of the tubers. It is advisable to inspect them periodically throughout the winter.
In spring, the tubers are checked again, divided if necessary, and prepared for planting. With this care cycle, dahlias can return to the flower bed every year and bloom until the autumn cold arrives.
A Reminder
Earlier, we wrote about how to grow magnificent gladioli and store the bulbs until the next season.