Neem Oil is one of the best organic pesticides out there, because it comes from the Neem tree (Azadirachta indica). When you mix Neem oil with water and spray it on your houseplant/garden plants, instead of killing the pests on touch, the neem oil goes into the plant so that if any pest bites into the plant, it dies. Therefore Neem oil can help for a long time.

WATCH OUT : Neem oil WILL smell weird at first, so i recommend spraying your plants outside and put them in a shed or any warm place for a few days before carrying your plants back inside.

WATCH OUT : Using high concentrations of Neem oil at once, can cause sun sensitivity for your plants (which gives the leaves more chance to burn.).

Yellowing leaves often happens when the plant is overwatered. This means that the plant is getting water too often/too much. Most of the time overwatering can result in root rot.

Yellowing leaves can also be caused by cold temperatures, and stress by humidity/temperature chages/instability

But don't worry! Most of the time it is just an old leaf dying off. Which is totally fine! Leaves sadly enough don't live forever, so when it's their time, it is their time. 

WHY : Spikes on cactuses are an defense mechanism to defend the plants against animals.

The Old Man Cactus (Cephalocereus senilis) is coverd in spikes AND hair, which is used to fight cold temperatures in a cold desert night.

HOW : Cactuses don't have any leaves, so when the stem of the cactus grows, instead of the plant producing leaves, it grows hard (or soft-hair like) spikes. When the cactus grows, it uses energy (via photosynthesis) to push out spikes. 

Droopy leaves are often a sign of thirst, so give it some water. Maybe even consider fertilizing the plant.

Clear plastic pots are a must have, especially if you are repotting a treated sick plant, potting a propagation or just like to see how the roots are doing. Clear pots are also used to see when the soil is dry and ready to be watered or to see if the plant is root bound and ready to be repotted and to see the condition of the roots.

Terracotta is also great. Just like LECA they soak op moisture. Therefore it is perfect for moisture-loving plants!

The traditional plastic pots are fine too, you can tell if the plant needs to be repotted by seeing if the roots are coming out of the drainage holes (except for plants with really thick roots like Strelitzia's), and if you need to know if the plants needs to be watered, you use a soil probe, moisture meter, the finger method, or a wooden stick. 

Personally, i like the wooden stick method. I just stick it in the soil, and if it comes out wet and dirty, the plant doesn't have to be watered. If the stick comes out dry and with a minimal amount of soil, you may water the plant. This DOESN'T go for plants like cacti and succulents, because they rather be bone dry for a week or 4, than be watered every week. Because that causes root rot.

Watering schedules are often used by people with less interest in plants, people that are busy all the time or just people who doesn't want to check the plants every day. My water day is usually on a Wednesday, but when i see a droopy plant, a plant with dry soil or a plant that needs to be constantly moist like a Chameadorea Elegans, i water them.

Most Orchid's like to be repotted after the bloom period. Because in the wild, Orchid's grows on trees. So instead of using soil, you should use Orchid Bark.

Silver/green roots = healthy roots

Brown/mushy roots = unhealthy rotten roots. Cut them off!

Cut off the flower stalk, and wait 'till next year!

You can water your air plant by misting the leaves or putting it in a bowl of lukewarm water and let is soak for 60 minutes

Air plants collect water via tiny hairs. Air plants doesn't have any roots, so the leaves soak up the water. So ofcourse, slow-release fertilizer pills doesnt work on these plants, because there are no roots for it to work! You CAN fertilize these plants by putting some liquid fertilizer in a bowl full of lukewarm water.

In the wild, most Philodendrons grow in trees (except for a few kinds), so mimicking that by growing your Phildendron on a moss pole, trellis, coco coir pole or bamboo stake (or any other climbing method) would be great!

(Even the hanging Philodendrons!)

When you cut back the plant, in a month or 2, the energy from the old part of the plant now goes to new growth, the plant WILL grow further! This goes for most plants. Just plop the cutting in some water, and it'll root in no time, due to the big amount of nodes on the stem.

As the mother plant matures, it will grow corms/bulbs (little, weird-shaped ball-like seed) attached too the roots, when repotting the plant, you need to carefully pluck them off, place them in a few layers of water, and within a few weeks, tiny roots will emerge, and a shoot where the leaf will come out. Once the roots are about 1 inch long (2.5CM), it is ready to be put in soil and thrive! 

Stem cuttings are also a option, just cut the stem, place in a propagation glass full with water, place it in a warm and humid spot and watch as roots form in a couple of weeks-months!

Patience is the con of propagating, this goes for all plants, especially for ZZ plants (Zamiculcas Zamiifolia), which can take up to 6 months to even start rooting!

A node is a bump on the stem of a plant, which pushes out leaves, aerial roots and roots. de-activated nodes can be activated via propagation, or air layering.

Help is on the way, Didi! Pretty much all ferns like to be in high humidity. Now if the fern hasn´t grown in a big while, it can be because the plant is root bound. Alot of times when someone repots a plant, they don´t correctly loosen the root ball. This can cause the plant to stay in the shape of its previous pot. To prevent this, simply loosen the root ball while repotting. If the plant is too root bound for that, just rip off a few roots, so those roots are firmly touching the new soil. If possible, then try to remove most of the soil from the roots before repotting. Hope this helped!