Posts Tagged: spring
If you've been thinking about blanketing your garden with blanketflower (Gaillardia), you're in...
A pollen-covered honey bee forages on a Gallardia. (Photo by Kathy Keatley Garvey)
A black-tailed bumble bee, Bombus californicus, forages on a Gaillardia. (Photo by Kathy Keatley Garvey)
A Gulf Fritillary butterfly, Agraulis vanillae, flutters on a Gaillardia. (Photo by Kathy Keatley Garvey)
A monarch butterfly, Danaus plexippus, spreads its wings on a Gaillardia. (Photo by Kathy Keatley Garvey)
A syrphid fly, also called a hover fly or flower fly, stakes out a Gaillardia. (Photo by Kathy Keatley Garvey)
Pollinators aren't the only insects that like Gaillardia. Here a praying mantis lies in wait. (Photo by Kathy Keatley Garvey)
Spring doesn't "spring" on the University of California, Davis campus. Sometimes it skitters,...
A honey bee nectars on a rosemary blossom on Feb. 9 on the UC Davis campus. (Photo by Kathy Keatley Garvey)
Pollen-packing honey bee heads for an almond blossom on Feb. 9 on the UC Davis campus. (Photo by Kathy Keatley Garvey)
A honey bee singles out a tidy tip blossom Feb. 9 on the UC Davis campus. (Photo by Kathy Keatley Garvey)
"Well, yes, I would like some aphids for dinner," said every lady beetle (aka ladybug)...
A multicolored Asian lady beetle, Harmonia axyridis, chows down on an aphid while other aphids suck juices from the rosebud. (Photo by Kathy Keatley Garvey)
A multicolored Asian lady beetle on a rain-soaked rose leaf on the first day of spring, March 20, in Vacaville, Calif. Note the aphids below the beetle. (Photo by Kathy Keatley Garvey)
Rain-soaked lady beetle eggs on the first day of spring, March 20, in Vacaville, Calif. (Photo by Kathy Keatley Garvey)
This is a sad time to be an avocado. Winter's gone and temperatures are just ripe for flowering and the trees are going bust. So much so, that those sad leaves that have accumulated salts over the last year are being dropped and only flowers might be seen, especially on young trees. This is time for a little shot of nitrogen to encourage some new vegetative growth. Not a bunch, but a nudge. Several pounds per acre, something less than 10-15 pounds of N for a mature orchard and even less for a new orchard.
A commonly held belief is that if you apply nitrogen at the wrong time, it will push resources into vegetative growth at the expense of flower and fruit. This is somewhat true for annual plants that get most of their nutrients from outside sources (soil, air, fertilizer, water), but trees have a huge buffer in their storage organs (roots, stems, leaves, etc.). Most growth in trees occurs from this storage source and most importantly from photosynthesis and the sun. The more sun captured the more energy for flowering and fruit production.
So it is this competition for photosynthates that becomes the most limiting factor. When there is not enough to go around, the tree sheds fruit. If you see fruit dropping off a tree after applying a slug of fertilizer, it's a salt effect. Too much salt and it causes a water competition and the tree is stressed. It's not the nitrogen, but too much salt. With fertigation this is not so likely to happen as when dry fertilizers were applied and someone got too aggressive with the application
In fact a dose of nitrogen fertilizer is a good idea at this time when there are lots of flowers. This can encourage a flush of leaves that will protect the fruit that does set from sunburn and damage that would cause fruit to drop. A bit of nitrogen to encourage leaf replacement is a good approach to dealing with persea mite damage that occurred the previous season.
For further reading about the competition between vegetative and reproductive growth as affected by nitrogen (or little affected in fruit trees by nitrogen), D.O. Huett wrote a wonderful review of past research on this topic:
Also, if the trees have really defoliated, it might be time to do some whitewashing, south and west sides of branches, to prevent sunburn.
Avocado defoliated and ones in a balanced bloom
avocados in bloom
It's a glorious day, the first day of spring, and what better time to mark the occasion by visiting...
A honey bee foraging on ceanothus in the UC Davis Arboretum Teaching Nursery. (Photo by Kathy Keatley Garvey)
A painted lady, Vanessa carduii, finds a cut-leaf lilac, Syringa × laciniata, quite attractive. (Photo by Kathy Keatley Garvey)
Check out the pollen on this honey bee foraging on ceanothus. (Photo by Kathy Keatley Garvey)
A mournful dusky-wing butterfly (Erynnis tristis) on Spanish lavender. (Photo by Kathy Keatley Garvey)
Mother Earth, a mosaic ceramic sculpture by Donna Billick of Davis, overlooks the UC Davis Arboretum Teaching Nursery. (Photo by Kathy Keatley Garvey)
A torrent of emotions on the face of Mother Earth, the work of artist Donna Billick. (Photo by Kathy Keatley Garvey)