Beyond Seed: Getting your seeds to grow into plants,
and
Other ways of getting plant material
(Jill Nokes, 2001)
I. Planting
Late winter planting in a greenhouse
Processed and treated seeds will germinate if given the correct levels of temperature and moisture. Temperatures in a greenhouse or cold frame will vary according to region. Temperate forest optimum germination temperatures are 50-62 degrees F. This may be reached in January in the south, and May in the north. Time should be left after germination to allow hardening off.
Outdoor fall planting
Clean and plant in prepared beds as soon as possible after collection to simulate the conditions that a seed would be exposed to in a natural setting.
Spring planting
Some hardwood species require varying degrees of moist chilling, and will not germinate after treatment until the soil becomes warm (68-86 degrees F). They will not germinate in the fall. They may be planted in fall or held in cool dry storage over winter and planted in early spring in greenhouse or cold frame, or outdoors after danger of frost is past.
Aeration for seed germination
Aerating seeds in water for one or more days will enhance uniform germination. The aeration minimizes the chance that they will respire and run out of oxygen, and the washing will remove inhibitory substances. One or two days of aeration is sufficient for most. Do not allow to germinate in the water.
Pre-germination on moist paper
Germinate on moist sheets of newspaper or towels in greenhouse or cold frame. Make sure paper is moist, not wet. Control light and moisture by adding layers of paper over seeds. Remove and plant as seeds germinate. Tilt trays; this will encourage drainage and make long taprooted species grow downhill. Useful for species that germinate over a long period of time; you do not have to plant “duds”.
Fall planting in a greenhouse or cold frame
Temperatures may be regulated in a number of ways. Root growth may be encouraged by applying bottom heat. After last frost, plants may be hardened off and moved outside. Over-wintered plants are often stronger and better able to withstand seasonal temperature fluctuations.
Cold frames
In moderate climates, a cold frame allows earlier planting of seeds by providing protection and warmth. May be permanent or portable. Should be ventilated to prevent overheating or condensation and fungus-growing conditions. During very cold temperatures, plants may need to be moved indoors or portable heater needs to be installed. Cold-frame plants may harden off and adapt more quickly.
Containers
Seeds may be grown in flats, boxes or separate pots or containers. Large taproot plants need deep containers. Coarse-rooted plants may do better in containers that promote root pruning.
Air pruning
Taprooted species often grow out of the pot into the ground. When containers are lifted, the roots are broken. If the root stays in the pot it may become girdled. Types of root-pruning devices include pots with no bottom, copper-treated pots, pots with tiered or spiraled holes. Some users have reported not only increased root biomass but better stem growth.
Soil mixes
Any mix should be firm and dense enough to hold seedlings in place without being too heavy. They should have a constant volume, wet or dry. They should not be difficult to rewet (straight peat or clay). Should not get dry too quickly (should hold adequate water); should drain quickly enough to not be soggy and potentially anoxic. Should be free from weeds, fungus, insects. Local availability governs the particular mix of components (peat moss, perlite, sand, vermiculite, worm castings, etc.). Native soils may be required as a component to provide certain kinds of inoculum.
Beneficial soil microorganisms
Mycorrhizae, rhizobium, Frankia, and other soil microorganisms may be necessary. Particularly for some slow-growing native plants that form taproots or sparse roots. May be accomplished by adding native soil to the non-soil mix, or by inoculating the sterile non-soil blend with cultures of the desired organisms.
Indoor sowing
Container should be premoistened before sowing. Watering may wash away or bury seeds, particularly small ones. Most small seeds should be pressed into the soil, not buried. Some small seeds require only a sprinkling of fine sand. On the other hand, if large seeds are planted to shallow, they may dry out in the upper layer of soil. A basic guideline is to plant two to four times as deep as the diameter of the seeds.
Seedling diseases
Damping off fungi (e.g., Pythium ultimum, Rhizoctonia solani) will kill seedlings. Slow-growing or weak seeds are especially vulnerable. Soil media may be treated with fungicide before planting. Also, it may be minimized by following simple cultural practices: (minimize over-watering, avoid poor drainage, lack of ventilation or high humidity). High concentrations of soluble salts weaken seedlings and encourage damping off. Sphagnum moss inhibits the damping off fungus. Fungi thrive between 69 and 86 degrees F.
Field sowing
Till the beds to a depth of at least 6-8 inches. Provide soil mixture that is well drained and does not pack down or crust over. Ideal seed beds contain organic material to improve structure. Avoid using clay or peat moss. Fall sown seedbeds may be covered with a light mulch that may be removed in spring. Keep seedbed moist, especially for fall-germinating species. Protect against predators.
Transplanting seedlings
Transplant from flats when second set of leaves appears. Seeds sown too densely in flats will be difficult to separate. Minimize root exposure to air. Some seedlings are soaked in water and root stimulator before potting. Water immediately after potting.
II. Vegetative propagation
Advantages of cuttings
You do not have to rely on a good seed crop. Some seeds require elaborate treatments. You can take cuttings of some species over a long growing season. You may get a larger plant sooner than with seed.
Drawbacks to vegetative propagation
You may get many individuals from a genetically similar clone. This gives you no genetic diversity in the face of climatic variation or outbreaks of insects or disease.
The rooting process
Collect at the right time of year for the species. Stem or root is cut or wounded to trigger root development. A callus forms around the wounded plant tissue at the base of a stem cutting. Adventitious roots or new growing points emerge. In root cuttings, new stems form. Then the independent plant is transplanted to a separate container.
How new roots are produced
Meristematic cells exist within stems or roots. These cells are able to differentiate into roots, adventious roots or stems. Production of roots depends on five factors: inherent ability to develop roots, presence of root-promoting substances, location where the wound or cut was made, time of year and therefore type of wood, and proper environmental conditions.
Inherent ability to root
Age of cutting: the juvenility factor
Young plants (one year and younger) root more readily than old ones. Older plants may produce growth inhibitors not present in younger ones. The juvenile stage is actually different for every species. It may be prolonged by cutting back or coppicing older plants.
Location of the cut
Make bottom cut just below a leaf or bud, usually. Buds are the location of the production of auxins, which stimulate growth.
When to take cuttings
The time is not as important as the physiology of the wood. Some can be rooted year round, while others require new wood. New growth may be keyed not to time of year but to conditions like warmth or precipitation. Plants in the nursery may be “flushed” by watering and fertilizing.
Types of cuttings
Hardwood cuttings are taken during the dormant season form the wood of the previous season’s growth. Often the cheapest and easiest method, but may be slowest. Hard to root species may not root at all from hardwood. Semi-hardwood cuttings are taken during the growing season from wood that has finished its first flush of growth. Wood is reasonably hard, not too flexible, and leaves are mature. Softwood cuttings are taken from emerging tender shoots and growing tips. Softwood cuttings quickly wilt after being collected.
Hardwood stem cuttings
Wood with best potential is of moderate size, with carbohydrate reserves stored up from the growing season. Tips are not selected. Hormone treatment is beneficial. Well-drained bed and careful watering are necessary to prevent rot. Keep tops cool to inhibit bud break and subsequent drying out. Take in dormant season from wood of the previous season’s growth. Central and basal portions of stem have highest carbohydrate concentrations. Cut basal ends on a slant. Each cutting should have at least two nodes.
Rooting deciduous hardwood cuttings
Bundle cuttings. Bury upside down in well-drained boxes of sand or sawdust. Basal ends must be near surface so warm temperatures stimulate root growth.
Rooting cuttings of narrow-leaved evergreens
Take cuttings in late fall or winter. Require misting. They take a long time to root. Juvenile wood of young plants is better than wood from mature plants. Use rooting hormone. Stick immediately after they are gathered. In greenhouse, use high light, intermittent misting and bottom heat.
Root cuttings
Take from young stock plants in late winter or early spring when roots have plenty of storage material. Digging root cuttings from plants in the wild is usually too time-consuming. Cut distal ends at a slant. Plant vertically if you have room with proximal ends up. You may plant horizontally if you do not have space. Sections may be 2-6” long.
These cuttings are taken from late spring through summer from new shoots that have partially matured and are woody at the base. In climates with multiple growth flushes, cuttings may be taken after each flush. Survive best if mist bench is used. Usually 3-6” long with leaves removed from bottom half.
Softwood cuttings
Prepared from soft, succulent new spring growth of deciduous or evergreen species. Take from shoot tips of side branches after a flush of growth, but before branch becomes woody. Softwood cuttings are generally taken only for a few weeks of the growing season.
Selecting a plant to propagate from cuttings
Select from full-grown plants in the field. Collect early in the day when they are fresh and firm. Store in field in plastic bags with wet newspapers. Keep cool. Place in an ice chest if feasible. Do not cut into short lengths at gathering site.
Wounding
Some species requires some wounding at basal end to initiate callus. Hit with a hammer; cut with a knife.
Rooting hormones
Most contain auxins. Use IAA, IBA, NAA (indole-acetic acid,
indole-butyric acid, napthalene-acetic acid). IBA is recommended for root growth.
Has been used in conjunction with IBA. Collect willow stakes, cut stems into small pieces, soak in water for 24 hours, then decant. Save water, and soak basal ends of cuttings of other species in it for 24 hours.
Application of rooting hormones
Quick-dip method is recommended. IBA or NAA is dissolved in alcohol. Standard solution is 50% water/alcohol mixture. Dip ends for five seconds.
The proper environment for rooting a cutting
Bring longer cuttings in from field. Cut into shorter lengths. Treat with hormones. Place in optimum temperature of 70-80 degrees F for softwood or greenwood. Use misting or high humidity system and moist rooting media. Need ample light. Media must be clean, moist, well-drained, well-aerated.
Containers
Rooting media
Clean, sharp masonry sand has traditionally been used in rooting beds. Coarse or very fine sands used alone will not retain sufficient water. Peat alone is poor, but peat and vermiculite or perlite and sand are good. Some rooting works better if the pH is slightly acid; peat is good for achieving this effect. Soak media before inserting cuttings.
Controlling water loss
Rooting boxes are sometimes covered with a pane of glass or a plastic sheet. Keep in light shade and mist regularly.
Hardening off
Do not disturb rooting cuttings for at least two weeks. Continue misting until some callus or root growth occurs, then decrease. After potting and new leaves have developed, keep plants in light shade until significant growth is produced.