The good news is that dahlias are among the easiest flowers to grow! All dahlia tubers, regardless of size, will produce equally strong plants and prolific blooms. Use the steps below to help guide you through the growing process.
After purchasing your dahlia tubers, remove the dahlias from the packaging material and store the tubers in a cool (50 degrees is ideal), dark place until planting time.
Dahlias grow best in well-drained soil protected from wind. Full sun is ideal, but they will tolerate some shade.
Space your dahlias according to the size of the blooms: larger varieties should be close to 3' apart, while smaller varieties can thrive if planted about 2' apart.
In the spring, before planting, enrich your soil with organic matter such as manure, mushroom compost or garden compost from the previous year. Other non-organic products such as 5-10-10 or 10-20-20 may be used instead or in addition to your current soil treatments. Other soil-improving additives like sand or peat moss can be added if needed for proper soil drainage.
We currently have two locations where we grow dahlias. One is heavy in clay; sand is needed to help with drainage. The other location is very sandy; peat moss in addition to heavy composting is helping to build up the soil. Both types of soil can grow exceptional dahlias if properly cultivated.
Plant after last frost, from April 20th to June 15th in most parts of the country. Place the eye of the tuber between 4" and 6" deep horizontally with the eye facing upwards. You may choose to pound a stake into the ground at this point, next to the tuber, before you cover it. Otherwise, you may damage your tuber by pounding your stake into the tuber after it is already covered and starting to grow.
Dahlias have many surface roots and weeding is required to avoid stunted growth during the first couple months. After this point, the plants will overtake most competitors in the garden and shade out the weeds. After July, cultivate no deeper than 2" and no closer than 1" from the stalk. Unless the weather is very hot and dry (southern climates), dahlias will need very little water until they begin to bloom.
After blooming begins, water thoroughly: soak the ground every week to week and a half. Staking may be required if dahlias are taller then 3' and/or in windy areas. Larger dahlias (dinnerplate varieties) may require additional staking due to heavy blooms.
Beware of slugs, especially early in the season when dahlias are just appearing from the ground. Slug bait may be required around each tuber. Other pests such as earwigs, aphids and cucumber beetles can be damaging as well. Organic insecticidal soaps should be applied to affected areas as soon as they appear to stop the spread. Diazanon can be used as a non-organic but effective method for controlling insects. Any application of insecticides should be applied early in the morning or late in the day.
This is what many gardeners wait for throughout the year. Now you have an opportunity to enjoy the fruits of your labor with fresh flowers inside your home. Dahlias should be cut in the early morning or late in the afternoon when the sun's rays are off the plants. Place freshly cut dahlias in tepid (warm) water for about one half hour and then replace with room temperature water. Blooms will last in a vase from 3 days to over a week depending on the variety. Change the water frequently and avoid placing your cut flowers in a hot or sunny location.
Note: For longest lasting flowers pick your dahlias as cut flowers when they are about two thirds open.
If you choose to dig up your dahlia's tubers after the end of the growing season to use again next year, you can divide those tuber clusters in the fall or in the spring. Both are equally as effective but the eyes on the tubers may be easier to see in the spring. Whenever you choose to divide your tuber cluster, start by looking over the cluster and recognizing the eyes next to the stalk. You might wish to divide the cluster in half or quarters and then work on dividing it into individual tubers from there.
All adequate tubers must have at least one root with one or more eyes on it showing. The size of the tuber in no way determines the size of the next season's plant. You might find yourself throwing away what look to be good tubers without eyes. We do it every season by the thousands; not every root will produce an eye. Dahlias may be stored as individual tuber or as large clusters.
After digging, dry tubers with a fan or put in a well-ventilated basement. Once dry, place full clusters or individual tubers in any storage container with a fungus-preventing medium; we use Vermiculite but dry peat moss or fine chipped wood will work as well. Cover tubers with your medium and place in a cool, dry place. Tubers cannot get too hot or freeze without being damaged. Maintain a temperature of around 45- 50 degrees all winter until spring planting. It is important to check your tubers every 3 weeks and remove any mold or apparent moisture.