Whether dahlias are grown for cutting or garden display or for exhibiting at flower shows, if they are to do their best, they must be pinched or cut back about July 4 in the latitude of New York City.
The procedure in the case of the average variety grown for its effect in the garden or as a cut flower is to pinch or cut out the top of the plant. This encourages side shoots to grow from each remaining leaf axil and makes a bushy and compact plant.
Growing Procedure For Big Dahlias
The procedure for growing a huge dahlia measuring 12″ to 15″ inches in diameter is more involved.
When such a variety is 12” inches high (by July 4, at any rate), it is cut back to the first two sets of leaves. This must be done even though half the plant is sacrificed.
The cut, made right above the second set of leaves in a stem that often is quite large and hollow, should be V-shaped so that as new laterals develop, they can close the opening.
Meanwhile, until new shoots develop to close the opening, something must be done to prevent water from collecting in the stem and causing rot that may kill the plant. One way is to plug the gap with ordinary sealing wax.
A better way is to slit the stem near the base of the plant with a sharp knife. A small slit through which any water that enters the stem can drain out will not injure the plant.
Only the four laterals which break from the axils of the four leaves remaining on the plant are retained in the case of dahlias grown for exhibition purposes. Every other side shoot or “break” is removed as soon as it appears.
Ways To Time The Bloom
There are several ways of timing bloom to have a freshly opened flower for a particular show date. Depending on variety and weather, buds about the size of peas open fully in three to four weeks.
So that the best can be chosen, the terminal or center bud, as well as the two side buds, are allowed to become as large as peas. If the terminal bud is not deformed or injured, it is retained, and the two side buds are removed.
If the terminal bud is imperfect or coming along too fast for a particular date, it is removed, and the better of the two side buds is allowed to develop instead. As a result, side buds open a week later than terminal buds.
If a plant grows very quickly and shows indications of coming into flower before the desired time, blooming can be postponed by cutting the stem back to the first pair of leaves.
Very quickly, two new laterals will start from the stalk. The stronger can be selected in about two weeks, and the other can be removed. This postpones blooming for an additional week.
Securing The Plants
To keep plants from being broken by the weight of the flowers or by wind and rain, they must be tied securely.
I prefer the raffia to the cord because it is easier to cut, and the job is done quicker when I gather many blooms.
I place the raffia around the stems and loop it twice around the stake. Manipulated thus, the raffia will not slip up or down while plants are growing.
I also tie each stalk separately instead of encircling the entire plant so that I do not disturb the other laterals when I cut it.
Cultivation
On July 15, the dahlia sends out many tiny feeder roots. Because they grow near the soil’s surface, beds should only be cultivated on July 15. But until then, dahlia beds should be cultivated weekly and after every rain to keep the soil around plants loose and friable
After cultivation is discontinued and before a mulch is applied (about July 15), plants are fed for the last time. A handful of bonemeal and pulverized manure is given to each plant.
A potato fertilizer such as 4-8-6 (to help tubers become large and healthy) is broadcast over the bed about 6” inches from the plant’s base.
I apply a mulch at least 2” to 3” inches thick over the entire dahlia bed. Salt hay, straw, old leaves, or grass clippings all are excellent. Whatever material is used as mulch should be laid on heavily.
If the summer is hot and dry, plants need water. But water should never be applied to the foliage. Rather it should be applied to the soil.
A thorough watering that soaks the soil to a depth of 6” inches lasts for a week, even in the hottest weather.
A soil soaker hose does a good job. It puts water around the roots of plants and can be left unattended while the gardener busies himself with other chores.
Spraying and Shading Dahlias
Dahlias should be sprayed or dusted every week or ten days. I prefer to spray because I find it easier to cover the underside of leaves with a spray than dust.
Bordeaux mixture controls most diseases. The most serious insects are aphids, leafhoppers, and red spider mites.
A nicotine spray or Red Arrow controls aphids, DDT, leafhoppers, and Aramite or Malathion, the red spider mites.
Often the backs of large dahlias grown for exhibition become discolored by sun or rain before they open fully. This is particularly true of dark varieties. Therefore, I shaded plants with excellent results to protect them from the sun and rain.
As soon as the bud begins to show color, I place bamboo canes in the ground on each side of the bud about 6” or 8” inches higher than it.
I then take a closely woven bushel basket, bend its handles, and balance it over the bud by putting a stake through each handle.
I check the basket each day and raise it higher as the flower opens. I have found that baskets used this way protect buds from the elements and keep Japanese beetles (which do not go under them) from eating the blooms.
Cutting Blooms
Whether I cut blooms for display at flower shows or for arrangements, I prefer to do so in the evening after the sun has gone down. Then, I place the cut blooms in a container of cold water for an hour or two.
Then I insert the stems of large blooms in a pan containing 2” to 3” inches of boiling water, keeping them in it for a minute. This removes air pockets from the stems and seals them up.
Next, I place all cut flowers in a deep water container in a cool spot overnight.
The dahlias are ready for use in the morning, remaining bright for four to five days.
The gardener, with knife poised, is about to cut out the top of the plant (leaving two full sets of leaves) to induce it to make side shoots.
Only the four laterals that break from the axils of four leaves left on the plant can develop on dahlias grown for show.
If the terminal bud is perfect, all the side buds are removed when pea-sized. Stalks are tied with raffia to individual stakes.
Two bamboo tokens, placed in the ground, support a bushel basket over blooms to protect them from rain and sun injuries.
Dahlias, grown by the author, adorn one side of the path. The bed is mulched with salt hay, and baskets protect those intended for display.
44659 by Edward J. O’Keefe