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Hello and welcome to Down to Earth. Our question this week is on leaves that are turning yellow
and what fertilizer to use on them. First of all you need to ask yourself a series of
questions because fertilizer actually might not be the appropriate on yellow leaves. But
lets investigate lack of fertilizer first and lack of nutrients. If their yellowing
is on older, lower leaves or newer, upper leaves you are to decide that first. The overall
yellowing or yellowing with green veins is another good question to ask yourself. There
are two very common nutrient deficiencies in our area and they are a lack of nitrogen
and a lack of iron. It is very rare that other nutrients will be deficient in our soil. A
nitrogen deficiency will show some symptoms of overall yellowing on the older leaves and
that's because nitrogen is what we call a mobile nutrient. The plant will take nitrogen
from its older leaves and send that element to its younger leaves to try to protect itself
and keep growing in times of stress. But iron shows up as yellow leaves with green veins
on your newer leaves, not on the older leaves. And that's because iron is an immobile nutrient.
The plant can't take it from its older leaves and move it to its younger, newer tissue.
So most fertilizers do contain nitrogen but they don't all contain iron. So be sure to
read your label closely and look at your plant before you decide what to fertilize with.
There are three numbers on the front of fertilizers and they are nitrogen, phosphorus, and potassium
in that order. Micronutrients such as iron may be found on the back of the label. If
your plants are deficient, give them a quick fertilizer boost such as a liquid fertilizer.
Then go back and compost if you want to provide a lower amount, slow release fertilizer for
this season. But don't assume your plant needs fertilizer, look closely at it. It may not
be related to fertilizer at all, it could be many other problems; too much or too little
water; too cold or too hot weather.
Our plant this week is 'Superbena Purple' Verbena. It's a great verbena cultivar. It
has really dark green, fuzzy foliage and it has intensely dark purple flower. A very nice
contrast in our gardens. It's extremely drought and heat tolerant and it well full-sun. It
flowers all summer long with those beautiful purple flowers. They're very long lasting
flowers and they do fall naturally from the plant without looking messy so this plant
does not require deadheading. Do allow room for the plant to spread, it gets up to 4 ft
wide. It stays very short though so its considered a ground cover, it only gets 6 to 12 inches
tall, staying a little more on the short side of that. It does attract butterflies and it
takes off as soon as you put it in the ground and starts to really spread quickly. It doesn't
need much fertilizer but a light application of something slow release or compost is great.
Its hardy to 15 degrees so in hard winters it may be an annual. It also looks great trailing
over a wall, or a bed, or a container.
To do in your garden this month, we want to check for aphids, they begin to be more active
in the last few weeks with the morning weather. Also check for black spots on your roses and
spray those that are prone every 7 to 10 days. But look for black spots because you don't
want to spray plants unless you notice a problem.
We'd love to hear from you, visit KLRU.Org/CTG to send us your question or plant of the week
from your garden.