Question
The leaves on my vincas, geranium, and daisy are yellowing. It is quite hot here in the Rio Grande Valley (tip of TX). Do the plant need fertilizer, more water, or what?

Answer
It is difficult to say. If you have watered regularily and the soil stays moist, it could be poor drainge together with overwatering. Hot temperatures on soil which has not been mulched (mulch is a 2" layer of shredded leaves, shredded hardwood, etc placed on top of the soil) can also cause yellowing because of the rapid drying of the soil. Finally insects can cause it.

Since it appear to be all of them, I would check the moisture level of the soil.

If you are not watering daily, then I suspect draught is the reason. Water every day during the hot periods, and when you water, water deeply (water for a long time).

The best soil is one which is loose and aerated. You can achieve this by mixing a handfull of potting soil or compost into the planting hole when planting. Hard compact clay soil (especially unmulched) can hold onto water and saturate the roots. The symptoms may look like lack of water and watering in this case can cause overwatering.

Without knowing/seeing the circumstances, it is difficult to determine.

- provide good drainge for the plants
- water deeply when you water
- keep plants well mulched

If mulched, and with good drainage, you can water frequently to keep the plants hydrated.

If not mulched, it can be very difficult to keep a steady temperature in the soil root zone. If poor drainage, overwatering and underwatering can replace each other on frequent basis making care very difficult.