Home Horticulture

Template:EventLinksBox Home Horticulture is a trial event run in Division B and Division C for the 2022 and 2021 seasons. It is an event with both lab and exam portions that test knowledge about the practice of garden cultivation and management from home. Horticulture has also been a trial event in several states, taking the form of Horticulture Science (as run in Wisconsin) or simply Horticulture. Participants may bring one three-ring binder of any size, two calculators of any kind, and a soil test kit for the lab portion of the event. For all calculations, English units will be used as they are what is most commonly used in horticultural practices.

Plant Propagation

Plant propagation is the process of growing more of a plant from plant parts such as seeds and cuttings. Growing plants in this way is often used for purposes such as creating aesthetically pleasing plant decorations and food cultivation.

There are two types of propagation: sexual and asexual. Sexual reproduction takes the pollen & the egg and the genetic makeup of both parent plants to create the daughter plant, thus, the floral parts of the plants are usually involved in sexual propagation.

Sexual propagation may be the quicker & cheaper option, or it may be the only way to avoid the transmission of certain diseases; there is more genetic variation with sexual propagation. It takes a seed in a favorable environment for it to germinate and grow into a plant.

Asexual reproduction involves taking one vegetative part of the parent plant (stems, roots, leaves) and having it regenerate into a new plant, thus the new plant is genetically identical to its parent plant. It is quicker and easier, and it may be the only way to perpetuate certain cultivars.

There are many methods of plant propagation, listed below.

The common method is, as mentioned above, sexual propagation through seeds, of which are four factors affecting propagation: heat, light, water, and oxygen. Certain plants may require a period of chilling and/or freezing (stratification) or breaking/softening the seed coat (still stratification) to begin germination.

Cuttings take a vegative part of the plant (if it is asexual) that could be both herbacenous or woody and dipped in a rooting hormone (which may or may not be used) and placed in a material such as soil, sand, peat, etc.. The cuttings are given indirect bright light (root cuttings can be kept in the dark) and the process of propagation can days or months.

Layering roots a part of a plant by covering the middle part of a bent branch, anchoring it, and when roots appear, the branch is cut from the parent plant. Air layering involves splitting & opening the stem and surrounded by sphagnum (peat) moss then wrapped; once roots appear the moss is cut.

Division breaks clumps of plants (roots, bulbs, tubers) to form new ones, usually done when repotting container plants and replanted either in the ground or containers.

Grafting, although not true propagation, is a common practice where a plant is transplanted into another host plant; this is done a lot with fruit plants.

Some plants have shoots, which can be transplanted as they already have a developed root system. Runners are similar, which have attached offspring that have produced roots that can be easily transplanted.

Mother flowers have a corm (bulb) that grows smaller bulbs as shoots that can be separated and replanted.

Plant Seeds

A seed is produced in sexual reproduction, of which there are two different types: dicotyledons and monocotyledons. Dicotyledon seeds have two distinct embryonic leaves (cotyledons), while monocotyledon seeds have one singular embryonic leaf. A monocot stores the bulk of its energy in the endosperm, while a dicot stores its food in the two cotyledons. There are three main parts of a seed: embryo, endosperm, and seed coat. The embryo is the plant before it emerges from the seed; the endosperm stores most of the food (mostly starch); the seed coat are the protective layers that protect the seed.

When a seed begins to form and an embryo is fertilized, a zygote is formed, which divides into two cells. The bottom cell develops into a structure called a suspensor, which brings nutrients from the endosperm & anchors the embryo. The top cell divides to form a proembryo; more cell division forms a globular embryo--this is the phase where cells begin to differentiate. Cotyledons begin to develop in dicotyledons in a heart shape, which grows and elongates; cotyledons store food in the form of proteins or starch for use by the embryo. The maturing, expanding embryo crushes the suspensor; the mature embryo has an embryonic root with a radicle, an embryonic shoot, and one or two cotyledons (depending on the type of seed). The embryonic stem has an epicotyl, which is the area above the stem where cotyledons are attached; the hypocotyl is the point above the attachment, connected to the radicle.

Plant Germination

Germination (with seed plants) is the process of the plant developing in the seed, thus growing a seedling; along with that the radicule & plumule is thus grown. There are certain conditions that may allow the seeds to germinate and develop into a seedling. Most factors that influence germination are temperature, water, oxygen/air and occasionally light or darkness. How the factors affect germination depends on the variety and type of plant as the method of germination is determined by the ecological conditions of its native habitat.

Water: Most seeds store a food reserve of starch, proteins, and lipids; the food reserve is needed for the growing embryo. During germination, the embryo absorbs water (imbibition), which leads to expansion from rehydration in cells. The water is needed since mature seeds are extremely dry and need the water to resume metabolic processes. Following imbibition there is an increase in respiration which leads to metabolic processes resuming from either suspension or dormancy, which changes organelles in the embryo structurally; the seed coat expands, swells, and breaks. By the time the seed imbibes water, hydraulic enzymes break down the food reserve into useful molecules; and by the time the seed sprouts leaves and roots, the food reserves are exhausted so the plant now relies on photosynthesis to survive.

Oxygen: Oxygen is required by the germinating seed for metabolism, used in aerobic respiration, the main source of the seedling's energy until it grows leaves. Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment.

Temperature: Seeds and plants of varying species require a wide range of temperatures to germinate; even seeds of the same species may require different temperatures to germinate. Seeds often have a temperature range where they germinate; often it is 16-24℃ (60-75℉), while for some plants it is just above freezing, some cold (-2-4℃ or 28-40℉), and some between warm and cool. Continuing on with cold-temperature-germination, some plants require cold (vernalization) to break dormancy, while others remain dormant and not germinate if conditions are not favourable. Cold stratification is a process where dormancy is induced prior to light emission, thus promoting germination; 4℃ is usually cold enough to end dormancy for most plants. Some plants, on the other hand, require high temperatures in forest fires to crack their seed coats.

Light/Darkness: A certain amount of light or lack thereof is required for certain plants, especially for forest plants as there needs to be enough light in the canopy for the plant seedling to germinate.

Scarification: Something that is supposed to mimic natural processes of the wearing down of a seed coat, such as fire, soaking in a body of water for a long period of time, or passing through an animal’s digestive tract.

Sometimes, the appearance of radicle marks symbolizes the end of germination and the beginning of when the plant utilizes food resources stored in the seed; these are some of the two most important phases in the life of a plant as this is the time where the plant is most vulnerable to injury, disease, and stress. As the mortality rate between seed dispersal & completing establishment is so high plants produce many seeds. The germination rate describes how many seeds of a particular species and variety will germinate over a certain period of time, usually expressed in a percentage. Germination rate is useful in determining the amount of seeds required for a certain area or desired number of plants.

Soil

Soil Testing

Soil tests can show the health and fertility of a plot of soil based upon the nutrients present. The wrong pH levels, nitrogen, phosphorus, or potassium content of the soil can often make it harder for plants to thrive. Some plants also grow better in different soil conditions, meaning that after doing a soil test one can make adjustments to the soil properties so that the plant that is being cultivated can grow in its best soil conditions. For most plants (there are some exceptions), the pH of soil should be around 6.0 to 7.0 for them to thrive. If the soil is too acidic (lower on the pH scale), it is more prone to minerals that can be toxic when too much is absorbed, such as manganese. If the soil is too basic/alkaline (higher on the pH scale), plants can't take in the nutrients they need.

Resources

Wisconsin Horticulture Science Rules