How to discover new plants at home

Introduction - A guide to plant breeding written by Thompson & Morgan's horticulturists

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Perhaps it's a different colour to the normal shade, or maybe the blooms are larger, double or uniquely shaped or patterned? Or is the plant taller or shorter than usual, particularly compact or maybe it has produced unusual, coloured leaves?

If your answer is yes to any of the above, then you might just have something special. Even if your answer is no, then you can still try your hand at a spot of plant breeding to create your own new plants, thanks to this helpful guide.

This easy to follow guide will explain two methods of discovering new plants in your garden. Firstly, it will teach you how observation skills can help you recognise when an unusual plant naturally appears. It will also explain, step by step, how to breed your own plants by hand!

Plant breeding is not merely for boffins working in sterile laboratories or elaborate glasshouse breeding stations. Plant breeding can be fun and very rewarding especially when you bear in mind that every plant you raise has the potential to be unique. Basic skills for plant breeding are patience, good observation and a clear idea about what you are hoping to create.

You do not need much room or space. Some gardeners over the last 350 years have vied with each other to produce the ideal new plant in only the tiniest of back gardens. Plants like Calendula, Dianthus, Nasturtium, Nemesia, Petunia and many others can be grown in pots and will take up little space.

Plant breeding involves two basic methods: Selection and Cross Pollination. When using cross-pollination avoid the use of F1 hybrid varieties as they often have very involved parentage, which can slow down breeding in the early stages. F1 hybrids can, however, be a good source of variation when using selection to find new material. More about this later.

The Selection Method

Many new varieties have arisen in the past from the observation of an improved or different type growing in a batch of seedlings, (Poppy 'Angels Choir' is a good example, the first variety of this type was seen growing in a field of corn). Wild flowers in the hedgerow or the plants in your garden may throw up something different, referred to as a sport. The more plants of one type you grow the more chance there is of finding something different or unusual.

When selecting, you need a good pair of eyes. Be observant as you go around the garden, looking out for anything unusual, e.g. more petals than normal, some variation in flower size or colour, or differences in plant height or habit. When you see it, label the plant, describing its important characteristics (e.g. double flowers, dwarf etc.) and try to isolate it from other similar type plants so that no cross-pollination occurs. Take a photograph if possible as a reference or for comparison in future years.

How to Isolate

Isolation prevents your special plant with its different characteristic from being pollinated by its neighbour. One way of doing this is to carefully dig up the plant with minimum root disturbance, pot it on, and move it a good distance away. Be sure the plant is sufficiently watered during the process. High obstacles like a tall thick hedge form a good isolation barrier, preventing bees or other insects from cross pollinating the plants.

Another easier method, if digging up the plant is too risky, is to isolate the individual flowers. This can be done by enclosing a number of flowers with a large insect proof bag, either netting of some sort, grease-proof paper, or a plastic bag with small slits for ventilation (fig.1). Ensure there is no gap at the base of the bag for insects to get in. Use a soft wire twist or string to secure the bag but be sure not to bruise or damage the stem of the flower.

Pollination cages are another useful way of isolating plants (fig.2). They can be constructed using a light wooden frame that is covered with white muslin or insect proof netting, secured with drawing pins or heavy duty staples. A clear plastic sheet forms an effective lid. The cage can then be placed over the plant and secured to the ground.

Once plants are Isolated

Isolated plants or flowers will often still need to be pollinated to ensure that the seed will set. To do this, the flowers should be self-pollinated. This is when you use the same flower or a flower of the same plant to pollinate with. For instructions on pollinating, see 'how to pollinate' below.

Although self-pollination naturally occurs in some plants, other types like Papaver or members of the Compositae (daisy) family will need to be self-pollinated, due to self-incompatibility problems. Self-incompatibility is simply a built in mechanism in the plant that prevents self-pollination from occurring.

Harvesting Seed

When the seedpod is ripe (fig.3) it is best placed with a label into a seed packet and stored in a cool, dry place. Later, the seed should be extracted, cleaned and placed in a packet labelled with the name, special characteristics of the plant and date of harvesting.

Further Selection

The following season grow a fresh batch of plants from the seed you have saved, and prick out as many seedlings as you can thereby ensuring good results.

Try to plant the seedlings in isolation from other plants of the same type. As the plants grow and develop, pull out (rogue) immediately any that do not resemble your original selection. You could use your photo as a reference. You may be left with only a few plants, and could harvest the seed of all the plants together.

The selection process should go on until all or most of the seed sown produces plants resembling your new type very closely. You can then send the seed to Thompson & Morgan for trial!

Alternatively, as you grow out your selections, you may notice some further possible selections (those plants which look particularly good or exceptional different). Harvest seed from these individual plants and sow them out separately as new selections. This method can help you get to your desired goal quicker, as one plant selection may be closer to being ready than another.

The Cross Pollination method

When you deliberately set out to create a new plant variety, cross-pollination is an invaluable method in breeding. As an example, you could potentially create a dwarf yellow flowered plant by crossing a tall yellow flowered plant (A) with a dwarf red flowered one (B). The possibilities are endless!

Basic Process of Cross Pollination

Year 1: Cross plant A with B or vice versa, then harvest the seed.

Year 2: Grow out the results of the cross (referred to as the F1 generation) in an isolated area and harvest seed from these plants.

Year 3: Grow out the harvested seed. This next generation (referred to as the F2) is where you should find the results of your aim. Select plants that have the desired trait (using our above example these would be plants that are dwarf and have yellow flowers). Once selected the plants can be self-pollinated (pollinating the same flower or using a flower of the same plant), or crossed with a plant with very similar characteristics, if they are self-incompatible (see explanation previously given under 'Once plants are isolated').

Subsequent years: Use the selection method to get seed true to type, remembering to sow out seeds of individual selections separately to increase your chances of attaining seed true to type quicker.

Special Notes:

Sometimes you may have a problem with your desired plant trait coming through into the offspring. Under such circumstances you may need to back-cross some of the crossed plant selections with the original parent (either A or B, whichever has the characteristic that you are having problems with). The term back-cross simply refers to the method by which seedlings or offspring are cross-pollinated back onto one of the parents involved in the original cross.

It is very important to label your plants accurately, and to also keep a small sample of seed from every stage of the breeding, in case you encounter a failure and need to retrace your breeding steps.

How to Pollinate

Grow a bed of each of the two plant types to be crossed (in our example A and B). On the plant you intend to pollinate, any buds or flowers that have colour in them but have not yet opened should be used. Open the buds (fig.1) and remove the anthers containing pollen (fig.2 & 3). Dust pollen from the plant to be used as the pollinator onto the stigma of the one to be pollinated (fig.4). Plants can be pollinated either using a paintbrush or in some cases by rubbing the two flowers together. You can sometimes tell when the stigma is at its most receptive by the presence of a sticky or shiny solution appearing on the tip. In some plant types the stigma can also swell or change shape when receptive.

As you pollinate each flower, cover it with a bag or place an insect proof cage over the whole plant (see 'How to Isolate' above). Once successful fertilisation has occurred, plants have various trigger mechanisms which indicate success. Some will drop petals, on others the stigma will blacken and shrivel. After a period of time the ovule where the seed forms will begin to swell and ripen. Continue with more pollinations on other flowers as they open and label each cross with a lightweight label marked with non-fading ink.

Members of the Compositae (Daisy) family, e.g. Rudbeckia, Chrysanthemum, Tagetes and Dahlia have flowers made up of many tiny florets that open from the outer edge in towards the centre. These small florets should to be pollinated on consecutive days as they open inwards.

When to Pollinate

Mid morning is usually a good time to pollinate flowers. There is no dew on them and temperatures are adequate for the pollen to be effective. Avoid pollinating on a wet day, as any water on the pollen will kill it.

Special Notes

Healthy (not overfed) plants are essential for good seed production. Be ruthless when selecting and discard all but the best. This will save a lot of time and effort in the long run.

With either selection or cross-pollination you should send the seed to T&M only when a reasonable number of plants are fairly similar for the desired trait. Enclose a colour photograph if possible.

Knowledge of your plants will prove invaluable in your breeding work. Try to find out as much as possible about the genus or species you are working on before you start. This is also a good way to check that there are no similar plants already in cultivation before you submit your entry. Make notes on breeding and at various stages of the plants growth and development. It may be helpful to search the Internet and to contact organisations like the Royal Horticultural Society, to find out about groups interested in the same plants as you.

Vegatative breeding

If you spot an unusual plant out of a bunch of seedlings, either as a selection or from the result of cross-pollination, you can often reproduce the plant vegetatively (by cuttings). This can be a quicker alternative to replicating your plant than trying to ensure that the seed it produces comes out exactly as it should.

Simply take cuttings from the plant, preferably using material from the base. Also avoid the use of any shoot tips with buds or flowers on it, as they will produce poor plants. This type of method is generally more successful with perennial plants or shrubs as opposed to annuals. If you are provided with a choice of similar type plants, some will be better at reproducing vegetatively than others. They might have more plant material available for cuttings at the base or in the middle of the plant. If so they should be selected in preference to others.

When you have a suitable number of plants from cuttings send them to Thompson and Morgan. Place the plants in a zipped plastic bag with holes punched in the top for air movement. The area around the roots should also be wrapped in damp tissue so that the plants do not dry out. Then simply label, and package them in either a small box or envelope for shipment.

Plant Breeding Case Studies

Case Study: Foxglove Primrose Carousel

One of our customers in Suffolk, England spotted a very different Foxglove amongst those in her garden. The plant was unusually short and compact, and the primrose yellow blooms were appearing in whorls all around the stem, very unusual for a Foxglove.

The customer sent the seeds to us and our breeders further selected the original plant for 2-3 years in order to stabilise the habit, form and colour. The resulting variety was named Foxglove 'Primrose Carousel', which graced the front cover of our 1999 international Seed Catalogue and achieved worldwide sales of 81,000 packets!

An international star from humble beginnings!

Case Study: Marigold Mr. Majestic

One of our customers in Scotland sent in some seed of a tall, border Marigold with unusual, striped blooms that they had growing in their garden.

T&M breeders grew this plant on trial and acknowledged that it had a very different flower pattern and form, but the habit was rather unruly. They then crossed the plant with a modern, dwarf variety in order to reduce the height, and achieve a more compact habit.

The resulting variety was named Marigold 'Mr. Majestic', which has been popular with T&M's container gardening enthusiasts for many years!

A compact container plant bred from a tall border specimen

Send in your specimens

Once you are happy that your plant is suitably different to any others available and that a high percentage of the seed comes true, you are ready to send in a sample of seed (or, if you have chosen to follow the 'Vegetative Breeding' method, a few cuttings) to Thompson & Morgan.

Your entry should be sent, along with a brief description detailing the plant name and its main attributes such as height, spread, flower colour and size as well as a short statement stating how the plant is different to those currently available. Also add any extra information that you can offer and obviously some pictures.

Package your seed or plant cuttings carefully and send them by first class mail. Please try to post your entry early in the week, so that weekend delays are avoided.

Send your entry to:

  • The Horticultural Manager,
  • Thompson & Morgan,
  • Poplar Lane,
  • Ipswich,
  • IP8 3BU

For a copy of our terms and conditions please write to the above address.

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