Determining how much water a plant needs can seem complicated, but it’s actually quite simple once you understand the key factors. In this comprehensive guide, we’ll walk through everything you need to know to water your plants properly and help them thrive.
The Importance of Water for Plants
Water is arguably the most important resource for plants. It has several crucial roles:
- Transports nutrients from the soil into the plant
- Helps plants maintain structure and rigidity
- Allows plants to photosynthesize and produce energy
- Cools plants down on hot days via transpiration
Without adequate water, plants become stressed and struggle to function properly. Their growth slows, leaves wilt, branches droop, and flowers and fruits will not develop correctly. Severe water stress can ultimately kill the plant.
Factors That Influence Water Needs
When figuring out how much water your plants need, there are several key factors to consider:
Different types of plants have different water needs:
- Succulents – Require very little water and thrive with infrequent waterings. Too much water will cause rotting.
- Cacti – Also need very minimal water, similar to succulents.
- Orchids – Prefer slightly moist soil, but letting them dry out between waterings.
- Vegetables – Need consistent moisture for best growth and yield.
- Herbs – Vary in needs. Basil and cilantro require frequent watering, rosemary and thyme need less.
- Annual flowers – Require moist soil to fuel growth and blooming. Avoid wilting.
- Trees/shrubs – Require deep weekly soakings once established. Younger plants need more frequent water.
Your specific environment impacts how much you need to water as well:
- Climate – Plants in hot, dry climates need more frequent watering than cool, humid climates.
- Season – During summer’s heat, plants require more water than in winter.
- Sun exposure – Plants in full sun dry out quicker than shaded plants.
- Wind – Quickens moisture loss from soil and plant leaves.
- Elevation – Higher elevations are drier and plants need more water.
- Indoors vs. outdoors – Outdoor plants often need less frequent waterings than indoor plants.
Soil composition impacts how well it retains water:
- Clay – Holds moisture very well. A little water goes a long way.
- Loam – Balances water retention and drainage. Often ideal.
- Sand – Drains rapidly and dries out fast. Requires frequent watering.
- Potting mix – Usually dries quickly and needs frequent watering.
For potted plants, container size matters:
- Small pots need more frequent watering than large pots.
- Larger volumes of soil hold more moisture.
- Pots exposed to sun and wind dry faster than sheltered pots.
As plants grow, their water needs increase:
- Seedlings and young plants need less water than mature, full-grown plants.
- Larger, more established root systems can take up more water.
Signs Your Plant Needs Water
The most accurate way to determine when your plants need water is by paying close attention and looking for these signs of thirst:
- Wilting or drooping leaves
- Leaves feeling dry or crisp to the touch
- Soil is dry 1-2 inches below the surface
- Pot feels light when lifted
- Leaves appear less glossy
- Growth slows down
- Flowers fade
- Fruits stall in growth or ripen prematurely
Waiting until you see these visible symptoms of water stress indicates you’ve waited too long. It’s best to water just before plants get to this point.
General Watering Guidelines
As a very general rule of thumb, most indoor houseplants need watering approximately once per week. But many factors can alter this schedule. Let’s take a look at some general guidelines:
- Vegetable garden – About 1-2 inches of water per week, either from rain or manual watering.
- Annual flowers – Prefer consistently moist soil. Water when top few inches become dry.
- Perennial flower beds – Usually need about 1 inch of water per week from either rain or watering.
- Trees and shrubs – Require deep weekly watering to wet the entire root zone during first few years. As plants mature, they become more drought tolerant and need less frequent watering.
- Succulents/cacti – Allow soil to completely dry out between occasional deep waterings every 2-3 weeks.
- Foliage plants – Water when top inch of soil becomes dry. Most need watering about once per week.
- Orchids – Prefer slightly moist soil. Water when medium becomes almost dry, about once per week.
- Cacti/succulents – Allow soil to fully dry out between waterings every 2-3 weeks.
- African violets – Keep soil consistently moist. Water when top half inch becomes dry.
- Herbs – Require very moist soil. For plants like basil and cilantro, water every few days.
How to Tell When a Plant Has Enough Water
Some key ways to determine when a plant has received sufficient water include:
- Observe water draining from bottom of container
- Potting mix appears moist 1-2 inches below surface
- Potting mix feels cool and damp to the touch
- Potting mix clumps together when squeezed
- Pot feels heavy when lifted
- Soil water moisture meter reads “wet”
The amount of time it takes for water to permeate soil and drain from the bottom depends on factors like soil type, pot size, and plant size. Small pots may only take a few seconds to a minute, while large containers and beds may take much longer for water to penetrate deeply and drain.
Follow these tips for successfully watering your plants:
- Water early in the morning, so leaves can dry off during the day. This prevents disease.
- Water at soil level, avoiding wetting foliage. Wet leaves can promote fungal diseases.
- Apply water slowly and deeply, until it drains from the bottom of pots. This encourages deep root growth.
- For potted plants, only water when soil is partly dry. Sticking your finger in 1-2 inches is a good gauge.
- Outdoor plants typically need 1-2 inches of water per week from rain or irrigation.
- Infrequent deep watering is better than frequent shallow watering.
- Automated drip irrigation or soaker hoses can provide consistent watering for garden beds.
- Mulch beds to retain moisture during hot, dry periods.
- Adjust watering schedules according to weather and growth rate.
Common Watering Mistakes
Some common watering errors lead to stressed, unhealthy plants. Avoid these mistakes:
- Watering on a fixed schedule rather than based on soil moisture needs
- Applying too much or too little water for the specific plant type
- Watering too often, not allowing soil to dry out sufficiently between waterings
- Relying on a sprinkler system that waters plants shallowly
- Letting containers completely dry out before watering again
- Allowing plant leaves to remain wet for prolonged periods
- Not adjusting watering practices as plants grow larger
- Watering late in day so plants remain damp overnight
How Much Water Does Each Plant Need?
Recommended water volumes vary significantly depending on plant type, soil, environmental factors, and container size. Here are some general guidelines for how much water different plants need:
- Tomatoes – 2-3 gallons per plant per week
- Peppers – 1-2 gallons per plant per week
- Lettuce – 2-3 gallons per 10 sq ft of bed per week
- Squash/melons – 1-2 gallons per plant per week
- Carrots – 2-3 gallons per 10 sq ft of bed per week
- Petunias – 1 gallon per 5 plants per week
- Marigolds – 1 gallon per 5 plants per week
- Zinnias – 1 gallon per 3 plants per week
- Geraniums – 1-2 gallons per 5 plants per week
Perennials and Shrubs
- Daylilies – 2 gallons per 3 plants per week
- Lavender – 1-2 gallons per plant per week
- Hydrangea – 2-3 gallons per plant per week
- Blueberry bushes – 5-10 gallons per plant per week
- Young trees – 10-15 gallons per week
- Mature trees – 20-30 gallons per week
For potted plants, the container size and number of plants per pot are key factors determining water needs. For example:
- 6 inch pot with 1 flower – 1/4 gallon every 5-7 days
- 10 inch pot with 1 foliage plant – 1/2 gallon every 7-10 days
- 12 inch pot with 3 succulents – 1/2 gallon every 2-3 weeks
Pay attention to drying rate rather than sticking to a fixed schedule. If soil dries quickly, increase watering frequency.
Measuring Water Amounts
To determine how much water you are applying, here are some key references:
- 1 gallon = 128 ounces = 3.78 liters
- 1 liter = 33.8 ounces
- A typical watering can holds 1-2 gallons
- 1 inch of water over 1 square foot equates to 0.6 gallons
You can place empty cat food cans in beds and pots to measure water depth. Drip irrigation systems and hose nozzles also have measurements to gauge water volume.
Determining exact water requirements takes time and observation. But following the guidelines here will set you on the right path. Pay close attention to your plants, environmental conditions, and soil moisture to dial in the perfect watering regimen. With practice, you’ll be able to keep your plants properly hydrated for vigorous growth and abundant flowers and produce.