Germinating Iris Seeds

Iris seeds germination

by John Coble and Bob Bauer

We have always (since 1982) germinated our Japanese and Siberian iris seed indoors. From some of our first experiments with this technique we had 80-100 % germination. With favorable weather we were planting 8-12″ seedlings in May with the first fan increases seen in July and in some crosses 100% bloom the following year. Our most vigorous seedling produced 8 bloomstalks on a one year plant!

Our main reason for germinating seed indoors is to gain one year on first bloom and thus one year on evaluation. most important is the elimination of unworthy seedlings and freeing garden space for another crop of seedlings. This does become important with an annual crop planting of 1000-1500 seedlings.

Germinating Iris Seeds

We collect our seed pods when ripe and starting to split, usually early September. The seeds are stored in paper envelopes-but for no more than a month. Be sure to shell your seed pods and search for and kill any worms. As soon as all seeds are collected, the seeds of each cross should be wrapped in pantyhose material (maybe cheesecloth would do).

These little tied up bundles are then put in a large bowl and covered with water – a saucer on top to hold the bundles down. The water should be drained and changed every day for at least two weeks. This soaking and rinsing treatment is to remove the seed germination inhibitor present in the seed or seed coat. Outdoors, the fall rains and melting snow in winter do the same thing over a 3 to 4 month period.

After the final rinse the seeds are covered with a 10 % solution of bleach for 1/2 hour. (10% solution created by mixing 1 part bleach with 10 parts water) Pour off the bleach solution and rinse quickly with water a couple of times. Then cover the bowl with plastic wrap and secure with a rubber band (do not seal with an air tight lid) or we transfer the tied bundles to a plastic bag and secure them with a twist tie.

The bleach treatment is to reduce the mould population that will want to grow on the wet seeds during the next stage, which is refrigeration (stratification).

The wet rinsed bundles in bowl or bag now need to be refrigerated for 12 to 14 weeks. Fewer than 12 weeks will find fewer seeds germinating. After the 12 weeks refrigeration the bowl or bag can be removed to room temperature (kept closed and moist). Some seeds may have already germinated in the refrigerator but most will start after the third day at room temperature.

After the third day, we get more germination if the seeds are warmed to 90-100 degrees F. for 1/2 to 1 hour each day. You can set your covered bowl of bundles in another bowl of hot water and let the seeds gradually warm up and cool back down. We fill the bowl of bundles with warm tap water, let sit until room temperature and then drain off the water until the next heat treatment the following day.

Tall bearded irises and day lily seeds are handled the same way through the soaking and refrigeration stages but not the warm water treatment after refrigeration. Bearded irises germinate best at 55 degrees F. Once your seeds start germinating handle them as best fits your needs and situation. This will depend on the number of seeds that you are handling, the size of your house and those you share the house with!

At about the fifth or sixth day at room temperature we open each bundle and remove the germinated seed to plastic cups half filled with wet sand and cover with plastic wrap. (separate cup for each cross) We continue this every other day for about a week. The ungerminated seed can then be returned to the refrigerator for a minimum of two more weeks and then the room temperature heat treating treatment repeated.

The germinated seed can be potted whenever you want. The other ideal of this system is that only germinated seed are planted. No trays of empty cubes from ungerminated seed. We raise the germinated seed on wet sand in plastic cups near a window. When we have sufficient number of seedlings with green shoots about one inch tall we transplant them with tweezers to seedling trays filled with a soilless seedling potting mix.

The trays are set about six inches below fluorescent lights; ideally the bulbs are about 1 to 2 inches above the tips of the plants. We use cool white bulbs and run the light 24 hours a day. We raise the lights until the plants are 8-10 inches tall. Then we let the seedlings grow to the lights and start mowing off the tips every couple of weeks as they grow into the lights. We fertilize every two weeks with a Miracid solution of one teaspoon per gallon of water.

Hopefully by mid-May the danger of frost is past and the seedlings can be hardened off outside for a week in the shade and gradually moved to full sun. Watch these tender plants, they will probably need watering every other day while outside, every day in the sunshine. Line out your seedlings in good organic rich soil and keep them watered all summer their first year (and mulched). The next spring you will have bloom.

Edited from AIS Region 6 Newsletter, January 1995 issue. Also appeared in the July 1995 issue of the CIS Newsletter. Coble and Bauer run Ensata Gardens in Michigan state and have introduced many new varieties of Siberian and Japanese irises. you may visit them on the intenet at:
With climatic conditions nearly identical to what we have here in most of Canada, their tips/hints on growing iris seedlings should be very helpful to most of our readers across Canada.

SIGNA Iris Seed Germination Guide

This guide was recovered from the Iris-L mailing list. It was apparently originally published by SIGNA (Species Iris Group North America). This is reproduced this as a public service to those who enjoy Iris culture.

Some thoughts about starting iris from seed

1. First of all make a list in a notebook of all the seeds you have received from SIGNA using the numbers assigned in the original list for later reference. Put down as much information as you have about each item, and leave some space to add more information as you learn it. Look up on the list where each item came from as listed on the front page of coded donors. (I try to order seeds that were grown where the climate is not radically different from mine if there is a choice.

2. Prepare labels for each packet at this time, being careful to use a waterproof pen or wax pencil. (My labels are usually pylon, a hard plastic with a hole at one end through which I thread a 6 to 8 inch piece of single strand telephone wire. But plastic knives will do to write the name and numbers on though you’ll need separate string or wire for fastening together. Rubber bands will NOT suffice.)

Seeds preparation

3. Most seeds need to be soaked in distilled water for at least an hour because they are “over-ripened”. This process is simple. I use separate containers (like jar lids) for each packet. Lay the label you’ve just made for this item over the lid of soaking seeds so you won’t get mixed up. Do each this way. (I use the kitchen table for this work.)

4. While the seeds are all soaking, all labeled, mix a quantity of peat moss, sand or vermiculite with enough water to dampen but not be soggy. Provide yourself with a box of cheap, plain sandwich bags. Now pick up a bit of wet moss (or sand or vermiculite) about the size of a walnut and make it into a ball which you hold in the palm of your hand. With the other hand poke a hole halfway down in the center.

Take the seeds from your first packet, that have been soaking, and put them in this hole and close it up again. This ball with the seeds neatly enclosed in the wet moss (sand or vermiculite) is then carefully placed inside a plastic sandwich bag in one corner. Now twist the wire on your label around the enclosed ball. (If you are using plastic knives you’ll obviously have to tie each in place with string or wire as rubber bands will deteriorate).

Iris seeds soaking

You have now processed your first package of seed! They can be “stratified” in the vegetable crisper of your refrigerator where they can safely wait for the next step, either planting outdoors or under lights. Continue putting each kind of seed in its own ball of wet moss (or sand or vermiculite), labeling correctly, and store them (at least three weeks, better two months).

5. Stratification of your seeds may be new to you, but it is important even if you intend to plant outdoors when weather permits instead of growing under lights. Heat and dryness kill seeds, so why not do the way the experts do and your percentage of germination will be higher. The seeds that are stratified can remain safely in a vegetable crisper for a long time, at least until all danger of frost is past in your area if you intend to plant directly in the garden.

This is very easy now, for the seeds are ready to, start growing right away and your labels are all made so you just make your row or rows and distribute your moist seeds, with the damp mix they were in, covering with a half inch of fine moss. Allow enough space at this stage and you can leave the plants in place until they bloom!

When you plant outdoors, the most important thing to remember (from now on) is to keep seeds and seedlings moist. Some people place a plate of glass over the seeds until they sprout. A board would do if you remove it as soon as they sprout (at least 8 days).

Growing on the window

6. If you can’t wait until all danger of frost is past you’ll need to provide a suitable environment indoors. You do not need a greenhouse. Select a sunny window in a room suitable for human occupation (so the temperature will be about right) and with the addition of fluorescent lights hung over your treasures, you can do fine.

You can plant each ball containing seeds in a separate 3-4″ plastic pot filled 2/3 full with either a commercial potting mix or a mix of your own.

They do not need fertilizer so a mix of half peat moss and half vermiculite will do (they’re sterile so you won’t have trouble with “damp off”.) Fit a new plastic sandwich bag over the top of the pot, snugly. As plants grow, gently increase the head room for growth, never taking the plastic off (you water from below). So now each group of seeds has its own little controlled environment. No drying out and no damp-off!

7. In providing adequate light, I have never found just a window sill and natural light enough in our climate. but you may be able to do that where you live. I use fluorescent lights with reflectors. “Gro-lux” and “Agri-gro” are lights especially made for growing plants under lights. I start out with the lights 6 to 8″ above the seeds, but raise them as needed.

8. Always water your pots from underneath (the moss acts like a wick). Keep the tops enclosed. If the trays you set your pots in do not have grooves for air and drainage, put some marbles or gravel under the pots. This drainage tray needs to be set in another tray to protect your table or window seat. I use boot mats for this because they are handy, cheap and have a rim around as if made for this purpose! Look for them in K-mart or other such store.


9. There is a wide variation in germination time. How cold the room is seems to matter, and the type of seed will determine how fast it sprouts, arils being probably the slowest. It may happen sometime that you will need to keep your seed-pots over another season if you want to get all possible plants. If you have kept track of how many seeds you planted you will know if they have all germinated.

10. Comments: Actually the depth to plant the seeds varies with the type of seed. Most need 1/2″ of milled moss over them but versicolor, louisianas or pseudacorus, all large seeds, would find this too shallow. When transplanting to their outdoor garden row, the roots must be accommodated as deep as they have extended with at least a half inch of soil over the crown.

As they grow they will seek a deeper or shallower space. A little dilute fertilizer solution can be given not oftener than once a month when first sprouted, then once a week, continuing until well established. I use a soluble fertilizer with a low first number.

11. By now you will have read about the types you have in back issues of SIGNA and made additional notes in your notebook including what you did and how, how much and when, your results and comments for yourself and for sharing. It’s a great project and you can be as scientific as your nature allows! This is how Mendel started!

12. If your list of iris seeds contains members of the ensata group (Japanese) you will need to test your soil to be sure it is acid enough for them, as they cannot withstand soils with lime in them. You may need to add “Miracid” or other acid fertilizer or soil sulfur when you transplant them to their permanent home. Most iris will tolerate a neutral soil, though spurias in general like alkalinity, as do most of the bearded irises.


If you have a wide variety of types you will want to find out their different requirements. Once established you’ll enjoy them all with a new appreciation. Every serious gardener should get his garden soil tested. The county agricultural agent usually will do this free or you can buy a kit and learn to test soil yourself.

A few growing tips: cristata have a tendency to grow out of the soil and appreciate a handful of moist moss thrown on them once in a while. Also, it’s easy to mistake their little stolons (Surface roots) for sticks to be cleaned off! On a hot summer day they like a sudden rain, but not the Junos. If it’s dry, remember to water the cristata.

But the Junos hate heavy summer rains when they want to go dormant as in their native land. So give them unusually sharp drainage and protection from the summer deluge, if you have one. Air circulation is important to ALL iris plants so be sure to keep them well weeded. They must be spaced far enough apart for the same reason. Don’t be tempted to plant other plants over their roots, either. Good luck and have fun in your iris adventure!