Issue: July 20, 1996

Picking ripe watermelons

Question: How can I tell when my watermelons are ready to harvest? Every year I waste several, picking them before they are ready or waiting so long they are overripe. Thumping them doesn't work for me.

Answer: Choosing a ripe watermelon is a challenge. In the field or garden it is much easier than in the store because you will have more clues. The indications to look for in the garden are the drying of the "pigtail" or tendril closest to the melon on the vine. If it dries while the leaves and rest of the vine looks good, the melon should be ripe. The tendril is not available to melon hunters at the grocery store. A second clue, which is available at the grocery, is the color of the "ground spot," the place where the melon rested on the soil. If this ground spot is yellow or a cream-yellow color, the melon is ripe. If it is green or white, it probably is not ripe. The rind at the soil spot should toughen and resist denting with a fingernail when the melon is ripe. Finally, for those with an ear for music or who can easily distinguish sounds, the ripe melon will have a dull thud when thumped, while the unripe melon will have a tighter, ringing or hollow sound.

New Mexico State University Extension Guide H-216, "When to Harvest Vegetables" is available at your local county Extension office. This publication gives guidelines for determining when to harvest 40 common garden vegetables, including watermelons, cantaloupes, and pumpkins.

Goatheads, goatheads, goatheads

Question: Since the rains came, goathead weeds are appearing all over my garden and lawn. What can I do? Can I use a preemergent herbicide?

Answer: Like many other weeds, goathead (called bullhead by some in New Mexico and puncture vine by others) seeds may lie dormant in the soil for many years until just the right conditions stimulate its growth. Our recent rains have provided the perfect conditions and the goatheads are growing where they haven't been seen growing so densely for several years.

You cannot use a preemergent herbicide to control weeds which have already germinated. Preemergent herbicides are to prevent the seeds from sprouting. Once the seeds have germinated you will need to use mechanical control, hoeing or pulling, or a postemergence herbicide labeled for controlling your target weeds.

It is important to know that there is no herbicide labeled for goathead weeds. The name you will see listed on the herbicide container is puncture vine. Look for a product labeled for post emergence control of puncture vine weeds.

Be sure to read the instructions carefully and follow the directions. Misuse of the herbicide can cause results you do not intend. Be sure it is safe to use the product you purchase in the garden or lawn. It should identify the environment where it is intended to be used. Using the herbicide in the wrong place may result in the death of desirable plants or contamination of food crops.

If you intend to use mechanical control techniques, be diligent and persistent. Learn to identify the weed in the seedling and more mature stages. Don't let seed form and mature. Remove the weed every time you see it. Don't delay. Though you may plan to return to the site, if you wait too long it will have made seed and you will have problems again next year.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!