Moist soil is almost always darker than dry soil, so when you see lighter brown coloured soil this indicates surface dryness. While this technique gives a general indication of plant dryness, it's best suited for plants that can be kept moist all of the time, such as Umbrella Palms and Boston Ferns.
Most plants benefit from drying out completely between waterings; some moisture-loving plants like ferns can be watered again when the soil is mostly dry.
Many potting soils become hydrophobic—tending to repel water—when they dry out, and are difficult to re-wet.
Gardening FAQ
The problem with your soil resisting hydration is not uncommon. It usually begins with the soil being watered incompletely and then drying more than it should. After that it can become hydrophobic and actually repel water! The ingredient in the soil that is causing that problem is peat.
A common reason is that the potting mix has dried out and isn't absorbing the water. Most commercial potting mixes contain peat, which holds water well once it has been moistened, but -- as everyone who works with sphagnum peat outdoors knows -- is difficult to wet the first time.
How can you prevent overwatering? The simplest solution is to only ever water your plant when the top two inches of soil feel dry (for cacti and succulents, water when the soil is fully dry). This gives your plants time to drink at a steady pace. Also make sure excess water can drain off.
Plants in containers dry out a lot faster than plants in the ground. Pots absorb heat, which can stress plant roots, and the soil in them dries out much faster than soil in the ground. Container plants generally need to be watered daily.
The best way to tell if your plants need water is to stick your finger about an inch into the potting mix—if it feels dry, break out the watering can.
The Finger Test. Simply stick your finger into the dirt as far down as you can and see if the soil is dry. When you remove your finger, any soil sticking to it indicates moisture. When your finger comes out relatively clean, it's time to water.
After a long dry period the earth becomes dehydrated. From dry weather or lack of watering, if soil is dead and lacks important organic ingredients it will actually repel water, rather than it soaking in when it rains or water is applied. This is known as 'Hydrophobic Soil'.
Wetting agents and washing detergents work the same way. The addition of ordinary washing detergent can improve the penetration of water in soil, but the effect does not last very long. Also many of these detergents contain compounds that are harmful to growing plants.
Plants can go to a maximum of a week without water, however, some plants can go for even longer periods of time, such as for two weeks or even a month. It would depend on the type of plant and its drought tolerance level.
Your containers need to be watered every day, especially when temperatures are so high. Sometimes you might even have to water in the morning and the late afternoon like we do in our Garden Center.
The best time to water is early in the morning when it's still cool, which preps the plants for a hot day, but that's not always easy to accomplish with a busy schedule. The second-best time is late in the afternoon or early evening.
Excess water collects in the bottom of the pot, so even if the top soil feels dry, the roots might be soaking wet. This leads to overwatering - which is the most common issue for plants without drainage holes.
The good news is that most plants will bounce back between 7-14 days if they're given proper care (which includes rehydration). If this isn't possible because major damage was done or little healthy root system exists then expect about 2 weeks until improvement can be seen.
Morning is ideal because it provides sufficient moisture to the plants for the entire day, there is less evaporation caused by wind and heat, and it allows wet foliage to dry out before nightfall. Watering in the evening is not recommended because the foliage does not have enough time to dry before the sun goes down.
In most cases, the soil should be damp to the root zone, 6 to 12 inches (15-30 cm.). However, sandy soil drains quickly and should be watered when the soil is dry to a depth of 2 to 4 inches (5-10 cm.). Remember that the need for water also varies widely depending on the plant.
Signs of root rot are slow growth, mushy stems, and wilting, yellow, distorted leaves (especially when the plant has been well watered, as wilting leaves can also be a sign of a dry plant).
It Grows Mold
Mold is another sure sign that your potting soil has gone bad. Mold usually grows on the surface of the potting soil and can be white, gray, yellow, or green. It can also be fuzzy or have a slimy texture.