Plants are very diverse and unique organisms. Each species has its own unique requirements for nutritional intake, light intensity, temperature, humidity, CO2 and pH of the medium or nutrient solution.

Further increasing the complexity, there are often multiple subspecies that can also greatly vary in their requirements for optimal growth. The good thing for horticulturalists is that although plant species vary greatly in their specific requirements, almost every plant species on the planet thrives with consistency.

So, in order to help your plants thrive it is important to understand the parameters required to supercharge the plants throughout all stages of growth.

Seedlings

Although seedlings from different plants will vary greatly in their requirements for optimal performance, most fast-growing annual seedlings share the same basic needs. By following some general rules of thumb, a gardener can achieve seedling success fairly easily.

During germination, the majority of summer plant varieties require warm conditions (usually 72 to 80°F). Spring or fall varieties of flowers or vegetables require lower temperatures for germination. A seedling heat mat is a must-have for any indoor horticulturalist.

This device, teamed with a thermostat, ensures consistent temperatures for even the most novice of growers. A consistent temperature throughout the germination stage is crucial to root development. Many plant varieties also benefit from higher humidities during the early stages of seedling growth.

A humidity dome, plastic bag or any other device that can be used to raise the humidity level around the seedling is beneficial. Unlike cuttings and clones, seedlings usually only require high humidity for the first day or two and then can acclimate well to the surrounding environment.

Nutrient requirements for seedlings are generally one-eighth of what is required for a mature plant of that particular variety. Most potting soils will contain more than enough nutrients to start seeds. If you are using an inert medium, add a very diluted fertilizer. You can use a diluted grow fertilizer (one-eighth strength), although few seedlings require high nitrogen at this early stage. Many horticulturalists supplement a blooming fertilizer at one-eighth strength to their seedlings with great success.

Cuttings

Most cuttings have similar requirements to the seedlings. Horticulturalists need to pay special attention during this stage of growth. Cuttings are more sensitive to large temperature and humidity variances.

Cuttings are usually most successful if they have their own grow space (note that some plant varieties are simply easier to clone than others). This is not to say that you cannot successfully grow cuttings in a vegetative room alongside other plants; however, having a specific place to grow cuttings allows the grower to have more control over the atmospheric conditions. Still, most plants have a range of desirable conditions that are almost universal when discussing the cutting process.

The temperature requirement for most cuttings is between 72 and 82°F, with the sweet spot usually right around 78°F. A heat mat can be a lifesaver in keeping consistent temperatures throughout the cutting process. In environments where temperatures stray too far from the ideal range, less than desirable results will occur.

If temperatures are too low, the cuttings will enter a state of suspended animation—that is, they will appear green and healthy but will never sprout roots. Eventually they will die or rot. Cuttings grown in temperatures that are too high usually soften and rot within a week without producing any viable roots.

This can be a problem for growers using aeroponic cloners in atmospheric conditions that are too warm. The submersible pump in aeroponic cloners produces heat that, if left unchecked in an already warm environment, can put the water temperature above the desired range.

This can be rectified by placing the cloner in a cooler environment or cycling the pump. A cycle timer can reduce the heat created by the pump by allowing it to cool between cycles. Sophisticated cycle timers allow the grower to set the on and off time down to the second or minute. A basic fifteen minute increment timer can work in a pinch for a grower with a hot cloner.

Consistent humidity is another crucial parameter in the cutting stage. Most plant varieties require high humidity levels for the first week or so. This is because the leaves still transpire moisture the way they did when they were part of the whole plant. If a cutting transpires more moisture than it is able to replace it will wilt and die.

In a high-humidity environment a cutting can retain much of its moisture and, therefore, retain its structural integrity. Growers should utilize humidity domes, ultrasonic humidifiers or any other device that can keep the humidity between 80 and 100% for the first five to seven days of the cutting process. After the first week, or at the first sign of roots, the cuttings can be slowly acclimated to their surrounding environment.

Nutrient requirements for cuttings are similar to that of seedlings. Most plant varieties require very little fertilizer for the initial cutting stage. High nitrogen fertilizers can actually hinder root development, so diluted blooming fertilizers or specific cutting fertilizers are usually the best choice for growers.

Vegetative stage

The majority of fast-growing annual plants have a vegetative stage and a fruiting/flowering stage. Throughout the vegetative stage most plants will thrive in a temperature range of 72 to 85°F. Keeping the temperature consistently within that range during the light cycle will be extremely beneficial.

Humidity for the vegetative stage can be much higher than that of the fruiting or flowering stage. The ideal range is usually between 60 and 80%. With the temperature and humidity consistently kept in the desired range, the plants are able to most efficiently use the light energy, nutrients, CO2 and water supplied by the horticulturalist.

When temperatures and humidity fall too far from the desired ranges the plant’s ability to photosynthesize is compromised, its metabolism slows down and all plant functions are no longer operating at optimal levels. Consistent temperature and humidity in the vegetative stage, teamed with adequate light energy and quality nutrients, results in accelerated, vigorous growth.

Nutrient intake for plants in the vegetative stage revolves around nitrogen. A good grow fertilizer will always have a higher ratio of nitrogen relative to potassium and phosphorus. Nitrogen is needed for fast, luscious, green growth.

The vegetative stage is the foundation for the future harvest of fruit or flowers and its importance should be recognized as equal to any other stage of growth. The more structurally sound a plant’s vegetative growth, the larger the fruit or flowers it can produce.

Fruiting or flowering stage

As fast-growing annuals finish their vegetative stage, they will enter the fruiting or flowering stage. This is the stage where they bear fruit or create blooms. Ideal temperature ranges for the fruiting or flowering stage are just slightly lower than that of the vegetative stage—usually around 70 to 80 °F, with no more than a 15 degree variance in the light to dark cycle temperatures.

The ideal humidity for the fruiting or flowering stage is 40 to 60%, which is significantly lower than that of the vegetative stage. Keeping an indoor garden within these parameters will ensure your fruit or flowers can develop quickly and to maximum size without being impeded by molds or fungus.

High temperatures teamed with high humidity in a bloom room are an invitation for a variety of pathogenic molds and a recipe for disaster. Low temperatures in a blooming room will dramatically slow growth and lower yields.

Consistency is also important in the temperature difference between the light and dark cycle of a growroom. Repetitive temperature fluctuations that exceed 15°F can create condensation, which raises humidity and increases the likelihood of pathogenic mildews.

Nutrient requirements for the blooming stage require a lessened amount of nitrogen in comparison to the other macronutrients. Bloom fertilizers with high phosphorus and potassium are usually the best choice for any fast-growing annual plant. The reduction of nitrogen along with the increase of phosphorus will help trigger plant hormones specific to fruiting or flowering.

Once a horticulturist finds the optimal conditions for their given crop, the best way to continually maximize performance is to make those magical parameters as consistent as possible.

Consistency allows for the basic plant functions we all take for granted to function at full tilt. Variance from those optimal conditions will slow plant functions down.

Our goals as indoor horticulturists are not only to give the plants what they need to survive, but to create an artificial environment in which they can thrive. In order for plants to thrive, they must have their basic needs met—met in a consistent manner on which they can capitalize.