where should i grow them?
Morning sun, afternoon shade is bestDahlias need plenty of sunshine. Full sun is OK but hot weather can burn buds and bleach blooms, particularly large dark ones. A structure with shadecloth (50% white or cream is best) will protect the plants from the sun. The shadecloth should be over two metres high to give space for grower and plants. A vertical barrier of shadecloth on the side of the prevailing winds reduces wind damage on exposed sites.
If this is not practicable, temporary cover during hot periods – eg an umbrella or even an old sunhat tied to a stake – is quite effective. Growers on a smaller scale should be able to find spots where existing structures and plantings give adequate protection.
Beds should accommodate single or double rows of plants with enough space between them to provide access. Raised beds make both soil preparation and access to plants easier.
Dahlias are not too fussy as to soil type although they do best in slightly acidic ground. Because of their intense growth care is needed in light soils to ensure they get sufficient organic material, nutrients and water to thrive – soil preparation becomes especially important. In heavy soils rotting of the tubers can be a problem, especially if they are left in the ground over winter.
Avoid tree roots and those of large shrubs or climbers. If necessary, install root barriers to remove the competition. Raised beds can help although, in time, the roots may grow up into them.
Because dahlias are thirsty as well as hungry the addition of irrigation, such as a drip system, will save a lot of labour during the season.