Back to Info Sheets	Dahlia Planting and Care   Dahlias are tender bulbs which need to be stored indoors over winter.  They are available in a variety of colours, forms, and sizes. Dahlias need plenty of moisture and grow best in rich, open, well-drained soil.  They benefit from well rotted manure dug into the bed in the fall or spring before planting.  A fertilizer high in phosphorus and potash, such as 6-12-12, may be worked into the soil surface before planting.  Too much nitrogen promotes soft growth with few flowers.  Dahlia tubers will rot quickly in wet, cold soil; do not plant them until the soil is warm, in late May or early June.  Plant them in a sunny spot, preferably shaded at midday. If you want plants to bloom early, they can be started indoors about the middle of April.  Fill a deep, flat box with a good loam soil, lay the tubers on their sides with the buds pointing upward and cover with 3 - 5 cm of soil.  Water well and place the box in a warm location until growth starts.  After 2 to 3 weeks move to a sheltered spot outside during the day, but the tubers will require protection from frost at night. To plant outside, dig a hole 15 cm. Deep and loosen the soil well on the bottom.  Lay the tuber on its side with the shoots pointing upward.  Place a stake in the ground, about 10 cm. from the shoot while it can be driven down without doing any damage.  Then cover the tuber with 5 - 10 cm. of earth and pack firmly.  To get show type plants or bushy plants when growing tall varieties: as shoots appear pinch off all but the strongest one and fill the hole with soil gradually, as the shoot grows.  Do not mound the earth.  Bedding dahlias may be pinched back to 3 to 4 shoots. To conserve soil moisture, lay down a mulch of pine bark or straw.  When watering, soak the earth thoroughly.  The taller growing varieties require staking to keep them supported as they grow.  To increase the size and quality of blooms, dahlias may be pruned by removing some side shoots from the axis of the leaves,  leave four to six side shoots off the main stem. Dahlias are damaged by hot, dry weather, so remember to mulch and soak thoroughly if rainfall is low.  Earwigs, leafhoppers, and tarnished plant bugs can also cause plant damage.  To control insects, watch for signs of damage and dust or spray plants with an organic insecticide. After frost has damaged the tops, cut them down to about 15 cm above ground level.  Leave in the ground for a further week or so unless very heavy frosts are forecast.  Dig the roots carefully, so as not to damage tubers, and leave them upside down for a few hours to drain off surplus moisture.  When partly dry, store during the winter in frost - free cellar at 50 degrees Celsius with good humidity; or pack in slightly damped peat moss or vermiculite.  Tubers can be divided in the fall. To do this, cut the crown or stem in such a way that each tuber is connected by it's neck to a section of the stem that has a growing bud or eye; discard tubers that have no eye attached. Vol. 97  no. 2
© Murray's Garden and Horticultural Services Last updated: March 2, 2008