Benefic planets are more safe to strengthen rather than malefics like Saturn even when they are weak. Scrutiny of the birth chart is needed for determining which planetary influence is afflicting, for example a weak Sun and weak Mars have same indications as they both indicate a low fire and weak will, though the difference is that a weak Sun gives a poor self image and weak Mars may give lack of motivation.
Sometimes use gems or herbs can be more harmful than use of mantras, usually mantras are used to ward off planetary influences afflicting us, like a strong Rahu or Saturn. Normally it is not advisable to strengthen such planets with gems and herbs. Yantras too are useful and don’t have any side effects and must be used for planets afflicting us. If we use gems, the quality of gems and how we energies it is very important. Gems can function both on the higher or lower base of the planet, depending on how you use them. Used wrongly the gems can confuse or disturb one on the astral level which is why it is important to clear and empower them with mantras.
If Moon is weak (when waning or in Scorpio), one will be anxious, lack in emotional stability, fear intimacy, have weak emotions and have anemia, dry skin, constipation or weak lungs. Pearls set in silver when Moon is in Taurus or Cancer may be used on the ring finger. If suffering from phlegm or edema avoid using pearls. Avoid dark and black colours. Herbs like comfrey root, solomon’s seal, musali and shatavari are helpful. The mantra for the Moon is OM SOMAYA NAMAHA.
If Mars is weak (in Cancer) or aspected by malefics a red coral may be used if one is not suffering from fevers, ulcers, bleeding or excessive sexual drive. Dark colours, grays and browns, yellows must be avoided. Herbs like saffron and cinnamom may be used in combination with ashwagandha, guggul or ginseng. Turmeric, onions and garlic is also good. Numerical yantras are also used, planetary yantras are inscribed in copper and these can also be used for purifying water. Yantras must be energized periodically like gemstones. Gold and silver yantras are believed to have more power and also do not have side effects like gems.