T-budding - a grafting technique that consist of placing a bud from one plant into a T shaped cut in the bark of another tree. It is sometimes called shield budding.
tall fescue - a trurfgrass species that may be either:

1) a lawn weed when it is introduced randomly by a bird or the wind. It forms a somewhat circular pattern of wide, coarse texture, lighter colored grass which conflicts with the other grass species.

2) an improved turfgrass species that is adapted to shade, droughty soils and takes wear well. New cultivars of this species have been developed for use in general purpose lawns.
taproot - a tap root is usually the central root of a plant that goes deep into the ground. Most plants do not develop a true taproot but a few such as walnut, sassafras and oak trees do which makes them more difficult to transplant.
taxonomist - a person who spends his or her professional life studying and classifying living organisms such as plants. A taxonomist generally tries to find ways to group common plants together based on a systematic approach.

Originally, this classification was based almost entirely on physical observations of the various structures of the plants. At one time, most classifications were made based on similarity of flower parts but, as time has progressed, other criteria have been used more.

In recent decades, many changes in classifications have come about because of the use of genetic (DNA) studies. Many times, plants that originally "looked" related turn out to be unrelated biochemically.

Taxonomists often have advanced degrees in such areas as botany, biochemistry and other related sciences.
taxonomy - the branch of science that deals with the identification, classification, and naming of plants or animals.
temperate region - a zone of the world which routinely experiences freezing temperatures nearly every year and experiences four seasons. In temperate regions, the foliage of herbaceous perennials dies to the ground and the plants survive beneath the surface of the soil.

See tropical and subtropical
tender - in plants, a term used to describe a plant that may not be able to survive in local conditions. It is often applied to plants that cannot withstand sub-freezing temperatures but it could also apply to those that cannot survive hot, dry summers.

See Tender Perennial below.
tender perennial - perennials are those plants whose life cycle lasts more than two years. However, that only happens in a climate to which the plant is adapted. Humans have the ability to move plants around the world so many end up being used in climates where they cannot survive through their normal life span.

Many of the plants that are grown as bedding plants or "annuals" in Northern gardens are truly perennial in tropical or sub-tropical areas. When grown where the plants cannot survive the cold winter, they are called tender perennials.

Although it always seemed to be a confusing term to me, British gardeners use the phrase "half-hardy perennials" for these types of plants.

 
tendril - vines climb by a number of different mechanisms. Tendrils are modified stems that coil around objects and support the stem.
tepal - most flowers have sepals and petals that can be easily distinguished from each other. They are usually of different colors or shapes.

On some plants, these two structure are identical to each other and cannot be distinguished easily. These are then called tepals. They tend to be common in many groups of monocotyledons such as hostas whose flowers generally have 3 sepals and 3 tepals which look the same.
terminal bud - a bud growing at the end or tip of a branch or stem. It may also be called the apical bud since it is at the apex of the stem.
tetraploid - most plants have two sets of chromosomes (diploid) and get one set from each parent during sexual reproduction. Through plant breeding or other chemical manipulation, some plants are produced which have four sets of chromosomes and are called tetraploid.

Tetraploid plants tend to have thicker parts including leaves, stems and petioles. Their flowers tend to be larger and the thicker stems make them more upright plants. The color of variegations and base leaf color tend to be deeper in tretraploids also.

Be aware, however, that to know for certain that a plant is a tetraploid, certain laboratory tests are needed. Looking at the physical features alone, while helpful, is not always the final arbiter.

See haploid, diploid, triploid and tetraploid.
texture - in horticulture, there are several ways in which the term is used including:

1) visual texture as considered in landscape design is determined by the relative size of plants or plant parts. Large leaves, flowers or shedding bark show coarse texture while thin leaves, small flowers and smooth bark indicate fine texture.

2) tactile texture is determined by the feel of a plant part to the human touch. Smooth and rough tend to describe a range of textures.

3) soil texture refers to the relative size of the particles that make up a particular soil. Those soils dominated by large amounts of sand or grit are coarse textured while those with more clay tends to be considered fine textured.
 
thatch - a layer of organic matter that forms between the soil and the surface of the turfgrass in a lawn. It is made up of both living and dead material such as stems, roots and rhizomes, which are resistant to biological breakdown. It is NOT made up of grass blades from mowing. Grass blades are made up primarily of water and decompose quickly compared to the thicker material of grass stems, crowns and roots.
thinning - a pruning method that controls the size (height and width) of a plant. Thinning cuts may also be used to rejuvenate the plant, making it more vigorous, healthy and strong.
thinning cut - removing a branch or stem back to its point of origin in the next larger branch. This type of pruning cut will reduce the size of a plant but, unlike heading cuts, will leave a more natural look to the remaining stems.

See Heading Cut
three-cut method - whenever a saw is used in pruning landscape plants, either a two cut or three cut method should be used. This means that the first cut is made up from the bottom of the branch. If the branch is of a smaller, manageable size, you then make the second cut from the top down.

If the branch is quite heavy, you make the second cut about a foot out from the trunk and then the third cut goes downward just outside the branch collar and joins up with the first cut from below.

If you just cut downward with one cut, at some point near the main trunk, the weight of the branch will rip the bark from the tree beneath the cut leaving an unsightly scar and opening the tree to infections. This is avoided by making the first cut upward to break the bark on the lower side of the branch.
threshold - each person and situation will determine the amount of damage from a insect or disease that will be tolerated before applying a control measure. This threshold may range from tolerating zero damage to deciding to do nothing or anything in between. The key is to not automatically feel that every problem needs to be sprayed.

This is a consideration in Integrated Pest Management.
 
tiller - 1) a new plant that originates from the root or bottom of the original stalk, referred to as an offset or daughter plant. Certain trufgrass species spread by adding tillers to the side of their crown.

2) a machine built specifically for turning over the soil to prepare it for planting.

tilth - the physical condition of soil.
tip layering - method of propagation in which the ends of canes or branches of shrubs are buried in the soil causing new plants to develop from them
tissue - a group of cells, usually of similar structure, that perform the same or related functions. For example, xylem and phloem are vascular tissue of plants.
tissue culture

- a high tech form of asexual plant propagation. Tiny pieces of a plant are prepared under completely sterile conditions to prevent contamination by rotting fungi. The pieces are grown in a nutrient rich mixture called agar in test tubes under highly controlled conditions.If everything works properly, the plant pieces will multiply rapidly. Using this process, thousands of cloned plants may be produced in a very short period of time.

Hostas - Due to the growth hormones used during the tissue culture process, there is an increased chance of mutations or "sports" appearing in a large group of plants that originate from a single mother plant (explant). As a result, many new cultivars of hosta have been introduced after they were found in the tissue culture process. These are often called "tissue culture sports".

More on Tissue Culture.
topdressing - a method of applying soil amendments or fertilizers by scattering them over the soil surface while the plants are growing.
 
topping 1) item such as pepperoni that may be put on top of a pizza

2) a drastic pruning of the entire top of tree to bring the height down to a desired level. This is generally not a recommended pruning technique for landscape plants.
topiary - an extreme and often artful form of pruning in which plants are turned into living statuary. Often evergreens such as yews are trimmed to reflect animals or other objects.
top soil - the uppermost layer of soil, usually characterized by a higher quantity of organic matter and nutrients than the subsoil. This is the layer where plant roots grow for the most part.  
toxicity - a measurement of the negative effects of a substance to an organism. This may apply to a pesticide, poisonous plant or anything else. The LD50 is one way to describe a substance's toxicity.
trace elements See micro-elements.
translocation - the movement of water, nutrients, carbohydrates and other chemical substances dissolved in water through the system of the plant.
transpiration - evaporation from the surface of a leaf.
transplant shock - whenever a plant is moved from one spot to another, it will lose a certain amount of its root system. The future health and vigor of the plant will depend on how well it can re-grow the lost roots. Plants that are unable to do so will start to decline, lose foliage and branches, suffer from reduced vigor and may die. This is not caused by a specific disease or insect and is called transplant shock.
transplanting - moving a plant from one growing environment to another.
 
trellis - garden structure generally made of crossing pieces of wood and posts that is intended to support climbing plants.
tree - a woody plant that has a distinct, individual central trunk.

Images of Trees.
trickle irrigation - method for watering plants through a tube or hose that has micropores or emiters which release water at a slow pace directly to the soil around plants. This conserves water by limiting the amount of evaporation and directs the water directly to the root system of the desired plants.
triploid - most plants have two sets of chromosomes (diploid) after receiving one set from each parent during sexual reproduction. Through plant breeding or other chemical manipulation, some plants are produced which have three sets of chromosomes and are called triploid.

See haploid, diploid, triploid and tetraploid.
tropical - an area of the world which NEVER experiences frosts or freezing temperatures.

See temperate and subtropical
tropism - general term for the plant's response to various external stimuli. Phototropism is the attraction to the light. Geotropism is the attraction that pulls the roots downward.
 
true leaves - the first leaves that emerge from a seed are called seed leaves. They may have little resemblance to the mature leaves of the plant. The first set of leaves that are representative of the species are called true leaves.
trunk - the major vertical above ground stem of a tree.
truss - cluster of flowers usually growing at the terminal end of a stem or branch in plants such as rhododendrons.
tuber - a thickened, short underground stem, as in the potato. Like a stem, it has eyes (buds) that may turn into either roots or stems.
tuberous root - a thickened lateral root which fills up to store carbohydrates and sugars to help perennial plants get off to a start in the spring. There are no buds on tuberous roots as there are on tubers. Example is dahlias.
tubular flowers Flowers that resemble a bell being held with the opening in an upward direction.
 
tunicate bulb - a bulb that has a series of concentric layers of a papery substance on the outside. Tulips are a tunicate bulb.
turfgrass - a term which differentiates species of grass commonly used in lawns versus those generally larger types that we call ornamental grasses.

Kentucky bluegrass is commonly combined with perennial ryegrass and fescue in cool-season grass seed mixtures for the home landscape in temperate regions.
turgor pressure - internal pressure within plant cells that keeps them firm and solid. Lack of water reduces turgor pressure and causes the plant to wilt.
two cut method - whenever a saw is used in pruning landscape plants, either a two or three cut method should be used. This means that the first cut is made up from the bottom of the branch. If the branch is of a smaller, manageable size, you then make the second cut from the top down.

If you just cut downward with one cut, at some point near the main trunk, the weight of the branch will rip the bark from the tree beneath the cut leaving an unsightly scar and opening the tree to infections. This is avoided by making the first cut upward to break the bark on the lower side of the branch.
 

 

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