PLANNING YOUR DAHLIA GARDEN
Dahlias can be used many ways in your garden. Individual plants or small clusters within existing landscaping provide summer-long color and highlight. Long straight rows look impressive and are easily managed and accessed for cutting blooms.
Large dahlias can be situated as to provide background color for other landscape plants. Small dahlias can be intermixed with other plants or used as borders. If you want to cut lots of blooms you should plan for easy access to all sides of the plants.
SELECTING YOUR SITE
Dahlias will grow in nearly any soil as long as you have 12-14 of tillable depth. If your soil is shallow or rocky, build raised beds to increase the rooting depth. Poor drainage will encourage rotting that can affect overwintering and quality of tubers that are produced. If your soil shows signs of standing water or is constantly wet consider modifying the drainage or build raised beds.
Sunlight is important to dahlia growth and flower production. Your dahlias should receive a minimum of 8-10 hours of direct or slightly filtered light. Plant them in a bright spot. Deep shade promotes lanky growth and few blooms.
If you are in an area where daytime temperatures consistently exceed 90 degrees providing shade during the hottest part of the afternoon will improve bloom quality and reduce fading.
If you are in an area that does not have consistent summer rainfall, be sure your dahlias are planted where you can provide regular irrigation.
GROWING DAHLIAS IN CONTAINERS
Dahlias do very well when grown in large pots or garden boxes. This is a good strategy if you have limited space, want to use dahlias as patio decorations, or if gophers are a serious problem. They do best in containers that hold at least 12-14 of potting medium. Smaller containers will require more frequent watering.
Always used the highest quality potting mix that you can find. If your container dahlias are regularly wilting even when watered regularly, move them to a location with less afternoon sun to keep them from overheating.
SELECTING VARIETIES TO PLANT
Dahlias range widely in height and foliage color, as well as bloom size, color, and form. The bloom size, color, and forms are classified by the American Dahlia Society in the US and Canada, and by the National Dahlia Society in the UK. We use the American Dahlia Society system to describe the dahlias in our catalog. In addition we list separately plant height to help you select the right dahlias for your collection.
A good garden dahlia may be compact, as noted by the height description, but also blooms over a long season and requires minimal staking. These are good choices for dahlias that will be easy to manage, combine well in your landscape, and reward you with loads of flowers.
A good cut flower dahlia blooms profusely over a long season, may have particularly stunning form or color, and has long, strong stems and good bloom substance. These dahlias are a good choice if you want to share or display lots of dahlias through the season.
GIANT BLOOMS VS. SMALLER BLOOMS??
Dahlias with giant (10"+) blooms are dramatic and fun in your garden. A 12" dahlia bloom is an amazing thing to see. They do usually require extra staking to support their weight. These giants often take longer to bloom and produce fewer blooms than the smaller types. Dahlias with smaller blooms will bloom earlier and are quicker to rebloom, rewarding you with more flowers over the season than the giants. Smaller blooms are easier to use in bouquets and arrangements than giant blooms. So if you are looking for drama in the garden giant dahlia blooms will certainly deliver, but if you are looking for lots of blooms to cut for bouquets we suggest you select from the smaller blooming varieties.
DAHLIA SIZE AND FORM TERMINOLOGY -
Illustrated at right
Form - Symbol - Bloom Diameter
Formal Decorative - FD - 4"-10+"
Informal Decorative - ID - 4"-10+
Semi-Cactus - SC - 4"-10+
Cactus - C - 4"-10+
Incurved Cactus - IC - 4"-10+"
Laciniated - LC - 4-10+"
Ball - BA - Over 3.5
Miniature Ball - MB - 2"-3.5
Pompon - P - Up to 2
Stellar - ST - 2"-8"
Waterlily - WL - 2"-8"
Peony - PE - 2"-6"
Anemone - AN - 2"-6"
Collarette CO - 2"-6"
Single - S - Over 2
Mignon Single - MS - Up to 2"
Orchid - O - 2"-5"
Novelty - NO or NOX - 2"-10"
PREPARING THE SITE
Dahlias do not require any more preparation than other bedding plants that you might be planting. Dahlias do well in high organic matter soils. We recommend working a 1-3 layer of compost into the top 12-14 of soil. You can also work in manure or a balanced commercial fertilizer at this time. Dahlias are heavy feeders and will benefit from additional fertilizer. Three to five pounds per 100 square feet of 12-12-12 is a very good starting point.
WHEN TO PLANT
Dahlia plants or cuttings provide the most flexibilty and the earliest start to the blooming season. They can be planted any time after the threat of frost has passed. They may be planted earlier if frost protection is provided.
Dahlia tubers should not be planted until soil temperature in the top 6 inches is at least 50 degrees. Tubers planted into cold soils will lay dormant and risk decaying before they sprout.
PLANTING YOUR DAHLIAS
The most successful method for planting dahlias is to use well established plants that are well rooted and have 2-3 pairs of leaves. Remove them from their containers and plant up to the first pair of leaves. Water them well on the day they are planted and water every 1-2 days for the first week in the absence of rain. After the first week to ten days reduce watering to weekly until they begin to actively grow.
Planting dormant tubers requires proper timing, soil temperature, and patience while waiting for them to sprout. Dahlia tubers should be set flat into a hole 4-6 inches below the soil surface with the eye pointing up. If the soil is dry, water them once on the day they are planted. Planted into wet soil they will need no additional water. Do not water tubers again until the shoots have emerged above the soil surface. This could be 2-3 weeks after planting. Dahlia tubers are very susceptible to rotting, which is why we recommend planting cuttings or plants.
Dahlias vary widely in plant size so there is no standard recommendation for spacing. Mature dahlias are usually as wide as they are tall, so a good guideline is to plant them 1/2 their height from structures or other plants. This means planting 6 tall dahlias 6 apart to realize the full potential of the plants. However, to maximize bloom production, space dahlias 1/2-1/3 their height apart, leaving more space on at least one side to allow access for bloom cutting and plant grooming.
STAKING YOUR DAHLIAS
Your plants will look better and be more manageable if you plan to provide some type of support for them. Dahlia blooms can be very heavy and nothing is more depressing than having a beautiful new bloom crash to the ground because it was not staked! Stakes should be driven at the base of the plant and be 1-2 shorter than the expected height of the plant. Tie the primary stalk to the stake in one or two spots as the plant grows. Maintaining your plants so that they grow upright, rather than sprawling will ensure strong growth and maximum flower production.
WATERING AND FERTILIZING YOUR ESTABLISHED DAHLIAS
After your dahlias are 6-8 tall and have 3-4 pairs of leaves you should supplement them with a water soluble nitrogen fertilizer. It is best to apply it by dissolving it in a watering can and dispensing a meaured amount to the base of each plant, or by injecting it directly into drip or soaker hose at the base of the plants. This should be repeated every 3-4 weeks through the season until about one month before the first expected frost. This will maximize their growth and flower production, creating strong plants with strong stems.
If your soil is sandy you should water lightly every 3-5 days. If your soil is heavy and has a lot of organic matter you can water every 7-10 days. Large, mature plants require more frequent watering than small plants. Dahlias do best if the foliage is kept dry. Occaisional overhead irrigation is ok to wash off plants or incorporate fertilizer. Wet blooms are prone to disease and can cause plants to topple. If your plants appear to be wilting increase the water frequency. Afternoon wilting on extremely hot days is natural as long as the plants appear to recover in the evening after the temperature has gone down.
Dahlias are the perfect cut flower producer. They respond to cutting by producing more blooms. Dahlia plants that have blooms removed regularly will produce more blooms than those that have blooms left on the plants. When cutting blooms from your dahlias take a fairly long section of stem. Plants cut back fairly hard will produce stronger regrowth from further down the stalk than if just the bloom is cut. Dahlias blooms are borne in clusters of three. Some growers choose to remove the two side buds to promote the size of the terminal bud. This is purely personal. You may choose to disbud some plants and leave others to grow naturally. Show dahlias are always disbudded.
If you are not regularly cutting blooms from your plants be sure to at least remove the spent, withered blooms on a regular basis. This is called dead-heading and is strongly recommended to reduce disease and unsightly debris on the foliage. Dahlias that are not regularly dead-headed may stop blooming entirely, very early in the season.
WHAT TO DO AT THE END OF THE SEASON
Dahlias are perennials and are not winter hardy. In nature the tops die back in the winter and growth the following spring comes from new buds formed on the roots. The same process will occur in your garden as the days begin to shorten and the temperatures drop in the fall. This cycle repeats indefinitely if the plants have good drainage and are not disturbed.
You have two choices when it comes to over-wintering your dahlias. Leave them in the ground or you can dig them out. We recommend leaving your dahlias where you planted them and enjoying them for a few seasons before digging them. If your soil is well drained and does not freeze solid you can manage them so they will return each spring for 3-4 or more years. Digging dahlias is laborious. It involves washing, dividing, labeling, storage, and replanting, often during the wettest and coldest months of the yaer.
Either way, to ensure your plants enter the dormant period in the best condition, withhold fertilizer the last 30 days before anticipated freeze or allow them to slowly decline in the fall to avoid lush growth at the end of the season. This promotes sound roots that will over-winter in the soil or the storage container in the best possible condition.
Learn even more about growing dahlias with the newly published guide from the American Dahlia Society, "Raising Beautiful Dahlias the Easy Way". This beautifully illustrated 80 page book will take you through every step of the season to get the most out of your dahlias. Click the link below to learn more.