Maintaining your Dahlias in Season
When your dahlias reach about 40-50cm it will be time to start staking your plants. Hopefully, you will have used the small stakes (popsicle sticks) at planting and this step should now be trivial. Simply remove the "starter" stake and replace it with the permanent one which will now provide support for the rest of the summer. If you didn't use "starter" stakes, be very careful about NOT DAMAGING your bulbs underground as you insert the stakes.
You can use many different materials to use as stakes. Bamboo, wood, metal, plastic are all satisfactory, especially if you paint them green in order to camouflage them. The size and material used should depend on the size of your dahlias - often a 1.5m-2m (5'-6') stake, pushed into the ground 25-30cm (10"-12") should be sufficient for most varieties. A stake which is too short or not solid enough can lead to your dahlias growing on an incline - or with the weight of some flowers, they may simply fall over.
During development, tie the main stem of the plant to your stake, leaving it loose enough to let the stem move around some. You can buy a green Velcro strip (from a roll) that you can cut to into varying lengths (which is also easily re-usable the following season). When the lateral branches grow, you can support them with string - attach one end of the string to the stake and gently pass the string under the new leaves, circling the plant, re-attaching the loose end back to the stake.
Watering your dahlias
Always consider several factors when trying to adequately water your dahlias; soil quality, outside temperature, drought, etc. ... In general, dahlias prefer a "good soak" a week - compared to several small waterings. A thirsty plant will tell you in two ways, either by withered leaves or stems with curved flower buds.
During the flowering season, it is important to remove flowers that are finishing their blooms for two reasons: it encourages more blooms (the more you cut, the more it will bloom). The second is that it lightens the stems and prevents breakage, especially for varieties with large flowers. Usually, the stems can support a large flower, but if a second bud on the same stem begins to sprout, the added weight of the wind and rain can easily cause breakage.
Insects can start wreaking havoc on your dahlias as soon as the first leaves begin to appear with cutworms and slugs. Later in the season the tarnished plant bug, equipped with its piercing-sucking mouthparts, can damage plant tissues by introducing digestive enzymes. When it attacks the growing points, the new leaves are deformed and can also prevent flowering. Flea beetles love to feed on leaves; aphids suck the sap, and the corn rootworm damages flower buds when they begin to open.
It is therefore important to check regularly during the growing season, responding quickly to any anomalies caused by insects. For further reading, click here.
Identifying your varieties
It is usually a good idea to start indentifying your dahlias near the end of the season, but before any signs of frost; frost will wilt your flowers and turn your stems and leaves dark - making the task of identifying them near impossible. It is important to note the plant color, the height, etc.. in case you will want to plant it in another area of your garden next spring. With digital photography, it has become much more simple to catalogue your plants.