Welcome ! I’ve compiled some quick dahlia growing information & resources for you on this page.
Growing Dahlias & Quick Resource Guide
Spanish Botanists discovered dahlias growing wild on the sandy hillsides of Mexico. The first tubers arrived in Europe at the end of the 18th century, sent over to Madrid by the Spanish settlers in Mexico. They have gained and waned in popularity many times over the years.
DAHLIA GROWING BASICS
Sizing & Eyes:
Dahlia tuber size does not dictate how well they will grow! Some varieties make TINY tubers, others make HUGE ones. The size of the tuber does not indicate how large your plant will become. We have tiny tubers that produce huge plants. Each tuber needs an ‘eye’ to sprout and grow into a plant.
Planting/Timing:
The rule of thumb is don’t plant dahlias until your soil temps are around 60-65. Since many gardeners don’t have a soil thermometer, wait til after last frost. In warmer climates, you can plant out earlier, such as April. Or in cooler climates you might want to wait. Dahlias do not like it cold and wet.
Planting Location:
Dahlias like full sun. You can do partial shade, the plant will get taller and potentially not give as many flowers. We don’t recommend full shade. Choose a well drained area, and you can also grow in pots.
How to Plant:
The general rule is around 3-5" under the soil line. Dig a hole large enough for the tuber to rest, and then fill in. If there is an eye, we try to point it up. Dig deeper if you need to amend your soil or add compost. We also add a local organic 3-5-4, this will increase foliage, bloom and root production all at once. Space around 15-18” for garden growing.
Watering and Care:
DO NOT water your tubers until you see a sprout. We wait til about 3-4" of growth. Dahlias can easily rot with too much water while dormant. This is why we do not wash our tubers-I don’t like introducing water to a tuber that is already 95% water. Do not plant in an area that holds a lot of water, Drainage is important. Plant in amended soil if you have heavy clay. We always lose a small % of dahlias due to spring rains, it happens. Once they are actively growing, they LOVE water. We water every 3 days in summer if we do not get rain. To keep your dahlias blooming, cut off the flowers when spent. If you do not cut the flowers, then they will create seed pods and that will signal to the plant that it's time to rest for the winter- so keep cutting to get more flowers.
Feeding:
We don’t give our dahlias too much nitrogen after the first month. This encourages big leafy plants with not many blooms. When we plant we do not amend our soil or add compost any longer-we get soil testing done. I also encourage soil testing to see what your soil needs are. Dahlias can be very heavy feeders but also react negatively to soil with nutrient issues. You will see deficiencies in leaf coloration or yellowing etc. Boron and manganese are two of the hardest to maintain. Soil testing is the best way to know how to amend your soil. We add the proper nutrients to our field every year vs adding spot fertilizing. However-for a general garden if you do not have a large field, I would suggest feeding with a balanced fertilizer, I like Sea Grow- 16-16-16 for the first feed. Maxi Sea also has a variety. You can purchase these on Amazon. Then you could add a blooming fertilizer with higher phosphorus-but this is only needed if your soil lacks phosphorus. Jacks Bloom Booster is a good one and Sea Grow has a 4-25-25 that we also like for spot treatments.
If your dahlias are growing but not blooming--make sure to cut the nitrogen. If your foliage is looking a bit stunted, you can feed with nitrogen and/or calcium and boron. Amazon has a variety of hydroponic micro nutrient fertilizers- we use Jackpot or MaxiCrop. There is no ‘one size fits all’ feeding regime for dahlias. For yellowing leaves or sickly foliage, we use the hydro micronutrient fertilizers which will also add iron and other trace/micro elements and micronutrients.
After Blooming:
Dahlia foliage will die back at frost and officially entirely die back at a freeze. Once this happens, cut back the foliage and dig the tuber with a shovel.
Dig down enough so that you do not break the root/tuber, it is very porous and water filled like a radish or potato and snaps easily. To store, a basement or garage that will not freeze works for the average gardener-- wash the tuber or not, but it is important that they are 'dry' before you put them into storage. Store with peat or pine shavings, and check on them in winter. Many tubers are lost in storage in winter… it took us a few years to perfect our storage-every situation is different.
In our 6b zone- you must dig your tubers at freeze or else once the ground freezes they will freeze. They are not hardy in our climate. I believe they are more hardy in zones 8 and above--but again we have only grown them in our climate, so please do the research on your own, there is so much info out there!
Last but not least, viruses. In the dahlia world, viruses are easily spread by snips and cuts you make on the plants and tubers. We spritz our pruners with bleach and/or alcohol, whatever we have handy between pruning and also in the field. It has kept our disease down - you can also adopt this in your garden if you so desire. There is a lot of info online about it.
Regardless, enjoy the process of growing! Once you are hooked on dahlias, you won’t ever go back! Thanks for growing with us!
DAHLIA RESOURCES:
Instagram Accounts Focused on Dahlias (Breeding or Sales)-Instagram is a WEALTH of information with lots of videos and photos of dahlias all year long!
@thefarmatoxford (our own account of course!)
@summerdreamsfarm
@coseytownflowers
@santacruzdahlias
@fiveforkfarms
There are also multiple dahlia Facebook Groups that I belong to:
If you are local to the SE PA area join → Dahlia Gardening in Southeast PA
US Dahlia Exchange, American Dahlia Society are a few more I love and are part of
Dahlia Addict is a website that consolidates all the varieties out there and updates annually with who sells what varieties. It is not always 100% accurate but is a great way to find a specific variety and who sells it.
Facebook has a wealth of dahlia groups as well. Breeding, Trading, Warm Weather groups etc. Definitely check it out.