Growing Exhibition Chrysanthemums

     In the fall of 1961 I attended a chrysanthemum show held at the Garden City Hotel.  It was the national show of the National Chrysanthemum Society hosted by the Long Island Chrysanthemum Society.  I could not believe the flowers they were showing.  6 and 7” flowers all grown outdoors without a greenhouse, in fact only outdoor grown chrysanthemums were allowed in the show.  Well I joined the LICS and over the years became a candidate judge, then a judge and now a Permanent Master Judge. 

     I would like to explain how anyone can grow these spectacular flowers outdoors.  It is really quite easy and first time growers usually do quite well if they exhibit in a show.

Location of the bed:  It is much easier if you have a bed exclusively for chrysanthemums.  It can be any size but you will find that it should not be wider than 3 feet and as long as you want.  You should have access to the bed from two sides.  The three foot width allows you to reach in from either side to tend to the plants in the middle of the bed and have access to both sides of all the plants. These plants require as much full sun as possible.  The more sun the better.  If you can’t provide at least five hours of direct sun in a day, you should try some other flower as you will not get great results.

Bed Preparation: Early in the spring the bed is turned over or rototilled as deeply as your back will allow. At least 8 inches deep. Five pounds of lime per 100 square feet is added together with three pounds of 5-10-5 granular fertilizer per 100 square feet. Peat moss or compost should be worked into the bed as you mix the lime and fertilizer in.  You are shooting for at least 25% organic matter in the bed and more is better.  Water the bed and forget it until June.  DON’T EVER STEP IN THE BED after this preparation.

Acquiring Plants: There are only a few nurseries selling exhibition mum plants.  They are not winter hardy in the New York City area, so every year you will have to purchase plants unless you have a way to dig the plants in the late fall and over-winter them in a place where it doesn’t freeze, but is still 35 to 400 and gets some light. (See the end for nurseries supplying these plants.) Plants are usually ordered in February and March for delivery around July 1st.  You will be receiving a small 5” high rooted cutting with about 1 inch roots.

Planting: It is best to plant these plants in 4” pots using one of the potting soils readily available in local nurseries:  Pro Mix, Scotts 450 etc.  They should be watered in using a water soluble fertilizer, Miracle Grow, Peters, etc. 1 tablespoon/gallon of water and placed in partial shade for a few days. They should be watered as required.  Gradually acclimate the potted plants to full sun over several days.  By July 7th they should be ready to be planted in the prepared bed.

            It is best to plant on 12” centers. When you are starting it is best not to try to grow too many plants and leave them at least 12” apart. In a three foot wide bed just plant two rows of plants.  Remove the plant from the pot by inverting the pot holding your hand over the top of the pot with the plant between two of your fingers and tap the bottom of the pot.  It will come right out and you will be surprised that some of roots have reached the inside of the pot.  Do not plant any deeper than they had been growing in the pot.  (Don’t “bury” the plant by putting soil on top of the soil in the pot.)  Water the newly planted plants with water soluble fertilizer as you did when you potted them up. Get used to using water soluble fertilizer as you will be doing it on a weekly basis until October 15th.

            The plants are now only 5 or 6” high.  When they bloom in October they will be approximately 36” high, so they have a lot of growing to do in a relatively short time.

            You don’t have to use mulch around the plants, but it does make life easier.  Buckwheat hulls are probably the best mulch, but they are not easy to purchase.  Coco hulls are good too and are more readily available.  You can also use fine pine bark mulch, which is probably the easiest to purchase.  Any of these mulches should be put down immediately after planting, about one inch thick. 

            The mulch has many advantages:  it holds moisture in the soil, it doesn’t allow the soil to get too warm from sunlight, it helps to prevent the soil from compacting from heavy rains and it prevents soil from being splashed up onto the leaves when there is heavy rain.

Care during the summer:  There are several things you must do during the summer growing period.  You must fertilize the plants with water soluble fertilizer every week, the same concentration you used when you potting the newly arrived plants and also when you planted them.  You should monitor the plants for any insect damage or the start of any fungus diseases and deal with these if they appear.

            I recommend blooming two or three flowers per plant.  You must have a stake for each flowering stem.  The stakes should be placed around the plant one or two weeks after planting.  The top of the stake should be approximately 30” to 36” above the ground after placement.  We put the stakes in the ground when the plants are young as the roots have not grown too much and thrusting the stake into the ground close to the plant will not cut any roots at that time.

            You probably wonder every day how a chrysanthemum knows it is fall and time to bloom.  Well let me tell you.  It measures the length of night.  As the summer wears on, night length gets longer and longer.  Obviously, day length does the opposite.  The length of night on August 24th in the latitude of New York is 10 ½ hours long and that amount of darkness will trigger the chrysanthemum to start to produce a flower. Each exhibition chrysanthemum cultivar (variety in lay terms) takes a certain number of weeks to actually have a flower from that August 24th bloom initiation date.  Some take 8 weeks, others 9 weeks, 10 or 11 weeks.  As you might imagine, a cultivar is called “an 8 weeker” or “9 weeker” etc.  This is known as the response group for the cultivar.

            So an 8 weeker will bloom on October 24th, 8 weeks after August 24th and these are the cultivars that I recommend you grow when you start this adventure. The small potted chrysanthemums plants you planted around July 7th will be 10 to 12 inches high by August 12th and will be one single stem.  These plants should now be pinched.  All you do is break off the top 1 to 2 inches of the plant.  If the plant is taller than 10 to 12 inches you can break off 4 or 5 inches of the top of the plant.  (If you want some fun, root the 4 or 5 inch piece you just broke off the plant.  They will root in 2 weeks.  (See below for advanced information.)

            You will find that about 10 days after this pinch, side shoots will rapidly grow out of each leaf axial (the connection of the leaf to the stem).  All but the two top-most shoots should be removed. These shoots will eventually become the flowering stems.  If you want to have three flowers per plant, leave the three top-most shoots.

            You will find that now in August the plant will grow rapidly and the remaining stems will elongate. When the stems become 5 or 6 inches long they should be tied to the stake for each stem.  I use twistems.  They are quite convenient as they can be un-done and moved up the stem as it grows.  As you move the twistems up the stem the one twistem per plant is all that you need.  You will continue fertilizing each week with the soluble fertilizer as you have been doing and continue to monitor for insect and fungus attack.

Flowering: By the third week in September you will finally see buds forming.  There will be a cluster of four buds at the end of each stem and a bud on a short ¼ to ½ inch long shoot in some of the leaf axial, mainly near the top of the plant, but that varies according to cultivar.  Some cultivars have buds all the way down the stem from where is grew after the pinch.  The leaf axial buds must be removed.  The cluster of buds at the top of the stem now takes your attention.  We leave the center bud and CAREFULLY remove the surrounding 3 buds.  When you are done, the stem has but one bud that sits directly at the top of the stem.  This bud will grow and around October 24th produce a 6 to 7  inch bloom.  Congratulations.

Protecting the bloom: This enormous flower can not stand rain falling on it.  The water will cause fungus diseases of the flower petals and will increase the weight of the flower so that any wind will break off the flower from the stem.  I cover my mum bed with clear plastic as soon as the buds show color, around October 1st.  This cover keeps off rain and dust and protects the flowers from frost.  Any frost touching the flower will turn it brown, so no frost can be allowed on the flowers.

After the bloom: The flowers will hold two or three weeks if left on the plant or at least ten days if cut and placed in a vase.  When it is all over, usually in late November, the plants are cut down to 6 to 8 inch stubs and the plastic cover removed.  Very seldom will they survive the winter if left in the bed. There are several ways to increase your chance of winter survival.  One is to dig the plant, put it in a pot and place the pot in a cold frame or a cold garage near a window.  Water it sparingly over the winter.  In the spring put the pot outside and begin to water it as needed and give it the famous water soluble fertilizer and see if it grows.

            Another way is to wait until the ground freezes and then put a heavy covering of straw on the bed to keep it frozen over the winter.  In the spring, remove the straw and hope for the best. If the plant does start to grow, no matter which way you brought through the winter you use the plant as a source of cutting material. (See below for rooting cuttings.)  You do not re-plant it and use it to produce flowers for the next year.  The old plant with it woody stem and old roots will not give you good flowers.

Growing in pots: Most of the exhibition chrysanthemums grown in the UK are grown in pots and many growers in this country are now doing it.  There are several advantages to growing in pots: you can completely control the soil and the nutrients in it, you can move the plants into a garage for shading (see below) or in case of heavy rain and it is far easier to control insects.  The disadvantage is you must watch the water as the pots dry out very quickly in hot sunny weather, especially when they get large.  Also, when the plants get tall, the pots will blow over very easily.

            Even though you will end up growing in plant is a 7 or 8” pot, you start off growing the plant in a 3 or 4” pot until you see roots coming out of the bottom of the pot.  It is then moved to a 6” pot and then finally to the 7 or 8” pot. 

            The potting mix is the same as you used to pot up the newly arrived cuttings.  The English sometimes make their own potting mix by digging sod inverting it and piling it up 3 or 4 feet high and leaving it for a year. The grass will have rotted giving the material a great deal of organic matter mixed with the top soil that had been adhering to the old grass roots.

            You must be very concerned about the nutrient levels in the pot all summer.  They should receive water soluble fertilizer once a week, but don’t over do it.

Additional topics:  Well now we know that exhibition chrysanthemums will bloom a certain number of weeks after the bud initiation date (August 24th in the New York area) and I recommended that for the first year that you grow only cultivars with an eight week response so they will bloom on October 24th.   Now you should expand your horizon and try to grow 9, 10 and 11 weekers.  How are we going to get these plants that would normally bloom on November 1st, November 8th and November 15th respectively to bloom on October 24th?  It is simple; get the 9 weeker to think it is August 24th on August 17th, the 10 weeker on august 10th and the 11 weeker on August 3rd.

The plant determines that it is August 24th by the length of darkness (10 ½ hours).  So for the 9 weeker we completely exclude light for 12 continuous hours (we could do it for 10 ½ hours but we allow ourselves a little wiggle room) on August 17th.  We do this by either moving the potted plant into a dark closet or garage at 7 PM and take it out at 7 AM the following morning or by covering the plant with a black cloth or black plastic from 7PM to 7AM.  This is called “shading” but it is actually the complete exclusion of light. 

This is done every evening until Labor Day.  In theory you could stop on August 24th but we always go beyond that date to be sure.

            You do the same for the 10 weekers (start shade on August 10th) and the 11 weekers (start shade on the August 3rd.)

            You probably think this is crazy but I’ve been doing it for 45 years and I am telling you IT WORKS.


Rooting cuttings: Chrysanthemums are very easy to root.  Cuttings can be any length from 2” to 6” long.  You break off the cutting; you don’t cut it with a knife.  The cutting should snap off easily without bending. Do not remove any leaves.  Even though the cutting doesn’t need a rooting hormone, I chicken out and use rootone or hormodin #1. These are white powders (they are mainly talc) and only a small amount will adhere to the cutting which is as it should be.  You just dip the bottom, cut end of the cutting in the hormone, tap the cutting on the edge of the hormone bottle to knock off excess hormone and put the cutting in the rooting mix.  You make a small hole in the mix with a pencil or your finger to accommodate the cutting.  You don’t thrust the cutting into the mix an it will scrape off the hormone! 

           Ah, you ask, what does the rooting mix consist of?  There are a lot of different mixes.  I use straight sand.  But you can use 50% peat moss and 50% pearlite.  Substituting vermiculite or sand for the pearlite works well too.

            The container you use to hold the mix can be anything: pots, flats, plastic food containers, etc.  as long as they are at lease 2 inches deep.

            The cuttings after being stuck in the rooting mix can not be allowed to dry out.  Commercially, the cuttings are misted with a very fine water spray every hour or so.  That is wonderful but really difficult for an amateur to accomplish.  Placing the entire container in a large plastic bag is much easier and works well.  The plastic prevents water loss and thus the cuttings stay turgid (full of water) without the need for additional watering.  The cuttings must have light to root but no direct sun light as it will heat up the air in the bag.  It is vital that they have a lot of indirect sunlight.

            The cuttings will root in two weeks.  At that time they will have ½ inch long roots (a “root ball” of 1 inch) and should be potted up just like you potted the newly arrived cuttings from the nursery and slowly acclimated to full sun. Do not think that it is better to leave the cuttings in the rooting mix longer to obtain longer roots.  Those cuttings with long roots developed in a unfertilized mix will cause the cutting to get woody and you won’t get the best flowers from it.

Thoughts:  My rhododendron friends, who for the fun of it looked at this section of the web site, probably think this all crazy and a lot of work.  Well when you see the flowers you get, you will understand why we go to this effort.  The Long Island Chrysanthemum Society holds a show every second or third weekend in October at Hicks Nursery in Westbury. In 2011 it is the weekend of October 22nd. Come, look at the flowers, there is no charge and say hello to me.