Cosmos & Zinnias
The first in our run-down of the top 10 easiest flowers for your cutting garden have got to be cosmos and zinnias. These two are reliable, colorful, and incredibly straightforward.
Let’s go through the process from seed to frost:
SEED STARTING
They need the soil to be about 70F to germinate, so you can set them in a warm window, or on an electric germination mat, or inside a pop up greenhouse, or turn a plastic tub over them outside (watch these last two closely because it will quickly become incredibly warm and you’ll want to vent them. A digital thermometer is a good idea).
Zinnias, 2021
TRANSPLANTING
When their baby leaves (cotyledons), fall off in favor of a couple of true leaves, you can carefully transplant them to your soil, as long as it’s staying above 50ish overnight. Transplant shock can be a little scary so If you have started your seedlings inside, it’s a good idea to “harden off” off by putting them outside (indirect light or you’ll burn their leaves) for most of the day and bringing them back in overnight. This way you acclimate them to wind, fluctuating temperatures, and daylight.
After they have hardened off for a few days, you can transplant them into their final container or garden spot! Amend the soil by mixing in a healthy dose of compost and bury them to the soil level of their seedling plug. Water them in so that any root system that was previously exposed to air is given good contact with the soil. Pro tip: Before I transplant out of their seedling trays, I douse them in fish fertilizer (diluted in water as directed on the bottle) so they go in the ground with lots of good nutrients and soaking wet. It helps dramatically to avoid transplant shock.
These plants can get pretty big, so plant them around 9 - 12 inches apart (if you aren’t planning on high intensity urban farming). I plant mine at about 6 inches apart, but I am moving through product at a rate that requires that spacing and if I was growing in a garden, I’d space it out a little bit more.
PINCHING
When they get 4 sets of true leaves on them, you’ll want to cut the top two sets off. It sounds brutal, but this type of plant needs that cue to branch and produce more stems. I use snips that have been cleaned with rubbing alcohol so I don’t transfer bacteria to an open cut on the plant, rather than actual pinching with my fingers. Cut them right above a leaf node and you cue the plant to bulk up produce multiple stems rather than one long hot mess of a stem.
FERTILIZINg
While the plant is putting on bulk and height, and while everything is still green, you want to fertilize with a higher nitrogen option. (Go back and read this post for info about fertilizers.) If you have a little sprayer, foliar feeding is a great option. If you don’t, root application is just fine.
Once the flowers begin to bud up, switch to a higher phosphorus fertilizer and stick to root application so you don’t ruin the blooms.
Cosmos, 2019
Harvesting & Conditioning
Cosmos are ready to harvest when you see the flowers beginning to open. Zinnias require one more step - we call it the wiggle test. If you see a zinnia flower that you think you’d like to cut, give the stem a gentle shake. If the stem is still wobbly at the head, it needs another day or two. If the stem remains rigid and the flower is stable on top when you wiggle, you’re all set to harvest!
Both plants prefer deep cuts. Don’t be shy. Take off the next three possible flower stems that make you nervous to cut. The plant will appreciate it and send you six more very quickly. If you don’t, they get tall, leggy, and weak, and your bloom quality will suffer.
Harvest in the morning or just before dusk. Try to avoid midday. They are in their biggest respiratory stage at that point and are completely dehydrated from the natural arc of the sun.
Pull off as many leaves from the stems as possible. They will hydrate leaves first after harvest, and your blooms will get the sloppy last bit and fade faster. Removing the leaves forces water to the bloom.
Cut at a steep angle and put them immediately into a bucket of plain, clean water. No preservatives or sugar or lemon or bleach. Move the bucket to a cool, dark place. In a few hours, your flowers will have recovered from harvest shock, rehydrated with the clean water, and will be ready for your designs! Pro Tip: Zinnias hate the cooler. Don’t put them in there. They will turn brown. Also don’t put flowers anywhere near fruit, in or out of the refrigerator. Fruit ripens and releases ethylene gas which, in turn, ripens flowers, taking days off of their vase life.
END OF THE SEASON
Cosmos and zinnias are both prone to powdery mildew and there is nothing that you can do about that except give them some better spacing so air can move through and prevent the mildew from growing. If you see it start to show up at the end of the season, don’t worry. It’s bound to happen. It is soil borne and it won’t go away without steaming the soil and even then it’s not 100% successful. It doesn’t affect the flowers at all and won’t hurt in future years. After the killing frost, you have a few options: (1) leave the stems the birds and insects to use and eat and help break down over the winter. (2) chop and drop, which just means cutting the stem a few inches above soil level and laying the debris down to hopefully begin to breakdown right there, returning all of the nutrients it pulled up to grow back to the soil. (3) chop and remove, which means cutting at soil level - leaving the root system in the soil to break down and host all those good microorganisms that help us grow things - and removing the debris to burn in cases of black spot or other confirmed disease. Depending on the plant, I do any one of these three options. This year it was all option one as we continued to work on the house.
